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<!-- Generated by DFIN XBRL Schema Document - http://www.dfinsolutions.com/ - on 24-06-2026 02:06:17 AM -->
<!-- Copyright(c) 2026 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<schema targetNamespace="http://www.nuveen.com/20260622" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:nifi="http://www.nuveen.com/20260622" xmlns:dei="http://xbrl.sec.gov/dei/2025" xmlns:srt-types="http://fasb.org/srt-types/2025" xmlns:deprecated="http://www.xbrl.org/2009/role/deprecated" xmlns:dtr="http://www.xbrl.org/2009/dtr" xmlns:oef="http://xbrl.sec.gov/oef/2025" xmlns:ref="http://www.xbrl.org/2006/ref" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xl="http://www.xbrl.org/2003/XLink" xmlns:us-gaap="http://fasb.org/us-gaap/2025" xmlns:oef-pre="http://xbrl.sec.gov/oef-pre/2025" xmlns:oef-lab="http://xbrl.sec.gov/oef-lab/2025" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:country="http://xbrl.sec.gov/country/2025" xmlns:us-roles="http://fasb.org/us-roles/2025" xmlns:enum2="http://xbrl.org/2020/extensible-enumerations-2.0" xmlns:us-types="http://fasb.org/us-types/2025" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:oef-def="http://xbrl.sec.gov/oef-def/2025" xmlns:negated="http://www.xbrl.org/2009/role/negated" xmlns:xbrldi="http://xbrl.org/2006/xbrldi" xmlns:srt="http://fasb.org/srt/2025" xmlns:oef-sr="http://xbrl.sec.gov/oef-sr/2025" xmlns:srt-roles="http://fasb.org/srt-roles/2025" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:stpr="http://xbrl.sec.gov/stpr/2025" elementFormDefault="qualified">
	<import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
	<import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
	<import namespace="http://xbrl.sec.gov/dei/2025" schemaLocation="https://xbrl.sec.gov/dei/2025/dei-2025.xsd"/>
	<import namespace="http://fasb.org/us-types/2025" schemaLocation="https://xbrl.fasb.org/us-gaap/2025/elts/us-types-2025.xsd"/>
	<import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>   
	<import namespace="http://xbrl.sec.gov/country/2025" schemaLocation="https://xbrl.sec.gov/country/2025/country-2025.xsd"/>
	<import namespace="http://fasb.org/srt/2025" schemaLocation="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd"/>
	<import namespace="http://fasb.org/srt-types/2025" schemaLocation="https://xbrl.fasb.org/srt/2025/elts/srt-types-2025.xsd"/>
	<import namespace="http://xbrl.sec.gov/oef-sr/2025" schemaLocation="https://xbrl.sec.gov/oef/2025/oef-sr-2025.xsd"/>
	<import namespace="http://fasb.org/us-gaap/2025" schemaLocation="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd"/>
	<import namespace="http://fasb.org/us-roles/2025" schemaLocation="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd"/>
	<import namespace="http://fasb.org/srt-roles/2025" schemaLocation="https://xbrl.fasb.org/srt/2025/elts/srt-roles-2025.xsd"/>
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				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ShareholderReport" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ShareholderReport"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ShareholderReportHoldingsDetails" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ShareholderReportHoldingsDetails"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ShareholderReportLineGraphDetails" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ShareholderReportLineGraphDetails"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ShareholderReportAverageAnnualReturnDetails" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ShareholderReportAverageAnnualReturnDetails"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/ClassOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#ClassOnly"/>
				<link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/LargestHoldingOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#LargestHoldingOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/Other1CategoryOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#Other1CategoryOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/AdditionalIndexOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#AdditionalIndexOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/BroadBasedIndexOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#BroadBasedIndexOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/Other2CategoryOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#Other2CategoryOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/SalesLoadOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#SalesLoadOnly"/>
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				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/IndustrySectorOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#IndustrySectorOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/oef/role/CreditQualityOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#CreditQualityOnly"/>
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					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000123979Member" order="5.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015115Member" xlink:label="C000015115Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015115Member" order="6.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015130Member" xlink:label="C000015130Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015130Member" order="7.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000202060Member" xlink:label="C000202060Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000202060Member" order="8.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015128Member" xlink:label="C000015128Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015128Member" order="9.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015126Member" xlink:label="C000015126Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015126Member" order="10.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015158Member" xlink:label="C000015158Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015158Member" order="11.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000171404Member" xlink:label="C000171404Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000171404Member" order="12.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015162Member" xlink:label="C000015162Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015162Member" order="13.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015172Member" xlink:label="C000015172Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015172Member" order="14.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000199174Member" xlink:label="C000199174Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000199174Member" order="15.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015168Member" xlink:label="C000015168Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015168Member" order="16.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015173Member" xlink:label="C000015173Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015173Member" order="17.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015175Member" xlink:label="C000015175Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015175Member" order="18.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000171405Member" xlink:label="C000171405Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000171405Member" order="19.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015177Member" xlink:label="C000015177Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015177Member" order="20.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015212Member" xlink:label="C000015212Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015212Member" order="21.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000123980Member" xlink:label="C000123980Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000123980Member" order="22.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015210Member" xlink:label="C000015210Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015210Member" order="23.0"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015208Member" xlink:label="C000015208Member"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ShareClassDomain" xlink:to="C000015208Member" order="24.0"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/Other1CategoryOnly">               
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_OtherCategory1Domain" xlink:label="OtherCategory1Domain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/Other2CategoryOnly">               
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_OtherCategory2Domain" xlink:label="OtherCategory2Domain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/LargestHoldingOnly">               
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_LargestHoldingsDomain" xlink:label="LargestHoldingsDomain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/SalesLoadOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_WithSalesLoadMember" xlink:label="WithSalesLoadMember"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists">               
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="InvestmentTypeCategorizationMember"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" xlink:label="InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="InvestmentTypeCategorizationMember" xlink:to="InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" order="1.0"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/BroadBasedIndexOnly">               
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_BroadBasedIndexDomain" xlink:label="BroadBasedIndexDomain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/AdditionalIndexOnly">              
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_AdditionalIndexDomain" xlink:label="AdditionalIndexDomain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/MaturityOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_MaturityDomain" xlink:label="MaturityDomain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/IndustrySectorOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_IndustrySectorDomain" xlink:label="IndustrySectorDomain"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/CreditQualityOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_CreditQualityDomain" xlink:label="CreditQualityDomain"/>
				</link:definitionLink>
				<!--GeographicRegionOnly use only for STPR-->
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/oef/role/GeographicRegionOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/oef/2025/oef-2025.xsd#oef_GeographicRegionDomain" xlink:label="GeographicRegionDomain"/>
				</link:definitionLink>
				<link:labelLink xlink:type="extended" xlink:role="http://www.xbrl.org/2003/role/link">               
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015105Member" xlink:label="C000015105Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015105Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015105 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015105Member" xlink:to="label_C000015105Member"/>
										<link:label xlink:type="resource" xlink:label="label_C000015105Member_2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xml:lang="en-US">Class I</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015105Member" xlink:to="label_C000015105Member_2"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015103Member" xlink:label="C000015103Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015103Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015103 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015103Member" xlink:to="label_C000015103Member"/>
										<link:label xlink:type="resource" xlink:label="label_C000015103Member_2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xml:lang="en-US">Class C</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015103Member" xlink:to="label_C000015103Member_2"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015101Member" xlink:label="C000015101Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015101Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015101 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015101Member" xlink:to="label_C000015101Member"/>
										<link:label xlink:type="resource" xlink:label="label_C000015101Member_2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xml:lang="en-US">Class A</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015101Member" xlink:to="label_C000015101Member_2"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="CommonStockMember"/>
					<link:label xlink:type="resource" xlink:label="label_CommonStockMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Common Stock [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="CommonStockMember" xlink:to="label_CommonStockMember"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepurchaseAgreementsMember" xlink:label="RepurchaseAgreementsMember"/>
					<link:label xlink:type="resource" xlink:label="label_RepurchaseAgreementsMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Repurchase Agreements [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="RepurchaseAgreementsMember" xlink:to="label_RepurchaseAgreementsMember"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015111Member" xlink:label="C000015111Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015111Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015111 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015111Member" xlink:to="label_C000015111Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000123979Member" xlink:label="C000123979Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000123979Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000123979 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000123979Member" xlink:to="label_C000123979Member"/>
										<link:label xlink:type="resource" xlink:label="label_C000123979Member_2" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xml:lang="en-US">Class R6</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000123979Member" xlink:to="label_C000123979Member_2"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015115Member" xlink:label="C000015115Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015115Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015115 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015115Member" xlink:to="label_C000015115Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" xlink:label="InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember"/>
					<link:label xlink:type="resource" xlink:label="label_InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Investments Purchased with Collateral from Securities Lending [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" xlink:to="label_InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015130Member" xlink:label="C000015130Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015130Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015130 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015130Member" xlink:to="label_C000015130Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000202060Member" xlink:label="C000202060Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000202060Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000202060 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000202060Member" xlink:to="label_C000202060Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015128Member" xlink:label="C000015128Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015128Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015128 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015128Member" xlink:to="label_C000015128Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015126Member" xlink:label="C000015126Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015126Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015126 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015126Member" xlink:to="label_C000015126Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015158Member" xlink:label="C000015158Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015158Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015158 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015158Member" xlink:to="label_C000015158Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000171404Member" xlink:label="C000171404Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000171404Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000171404 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000171404Member" xlink:to="label_C000171404Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015162Member" xlink:label="C000015162Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015162Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015162 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015162Member" xlink:to="label_C000015162Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015172Member" xlink:label="C000015172Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015172Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015172 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015172Member" xlink:to="label_C000015172Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000199174Member" xlink:label="C000199174Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000199174Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000199174 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000199174Member" xlink:to="label_C000199174Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015168Member" xlink:label="C000015168Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015168Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015168 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015168Member" xlink:to="label_C000015168Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015173Member" xlink:label="C000015173Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015173Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015173 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015173Member" xlink:to="label_C000015173Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015175Member" xlink:label="C000015175Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015175Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015175 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015175Member" xlink:to="label_C000015175Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000171405Member" xlink:label="C000171405Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000171405Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000171405 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000171405Member" xlink:to="label_C000171405Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015177Member" xlink:label="C000015177Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015177Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015177 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015177Member" xlink:to="label_C000015177Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015212Member" xlink:label="C000015212Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015212Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015212 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015212Member" xlink:to="label_C000015212Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000123980Member" xlink:label="C000123980Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000123980Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000123980 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000123980Member" xlink:to="label_C000123980Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015210Member" xlink:label="C000015210Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015210Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015210 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015210Member" xlink:to="label_C000015210Member"/>
					<link:loc xlink:type="locator" xlink:href="#nifi_C000015208Member" xlink:label="C000015208Member"/>
					<link:label xlink:type="resource" xlink:label="label_C000015208Member" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">C000015208 [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="C000015208Member" xlink:to="label_C000015208Member"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentTypeAxis" xlink:label="InvestmentTypeAxis"/>
					<link:label xlink:type="resource" xlink:label="label_InvestmentTypeAxis" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Investment Type [Axis]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="InvestmentTypeAxis" xlink:to="label_InvestmentTypeAxis" priority="1"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsNet" xlink:label="AssetsNet"/>
					<link:label xlink:type="resource" xlink:label="label_AssetsNet" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Net Assets</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="AssetsNet" xlink:to="label_AssetsNet" priority="1"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentCompanyPortfolioTurnover" xlink:label="InvestmentCompanyPortfolioTurnover"/>
					<link:label xlink:type="resource" xlink:label="label_InvestmentCompanyPortfolioTurnover" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Investment Company Portfolio Turnover</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="InvestmentCompanyPortfolioTurnover" xlink:to="label_InvestmentCompanyPortfolioTurnover" priority="1"/>                
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_NoTradingSymbolFlag" xlink:label="dei_NoTradingSymbolFlag"/>
					<link:label xlink:type="resource" xlink:label="label_NoTradingSymbolFlag" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">No Trading Symbol Flag</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_NoTradingSymbolFlag" xlink:to="label_NoTradingSymbolFlag" priority="1"/>		
				</link:labelLink>
			</link:linkbase>
		</appinfo>
	</annotation>   
	<element name="C000015105Member" id="nifi_C000015105Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015103Member" id="nifi_C000015103Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015101Member" id="nifi_C000015101Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015111Member" id="nifi_C000015111Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000123979Member" id="nifi_C000123979Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015115Member" id="nifi_C000015115Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" id="nifi_InvestmentsPurchasedWithCollateralFromSecuritiesLendingMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015130Member" id="nifi_C000015130Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000202060Member" id="nifi_C000202060Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015128Member" id="nifi_C000015128Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015126Member" id="nifi_C000015126Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015158Member" id="nifi_C000015158Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000171404Member" id="nifi_C000171404Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015162Member" id="nifi_C000015162Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015172Member" id="nifi_C000015172Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000199174Member" id="nifi_C000199174Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015168Member" id="nifi_C000015168Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015173Member" id="nifi_C000015173Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015175Member" id="nifi_C000015175Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000171405Member" id="nifi_C000171405Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015177Member" id="nifi_C000015177Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015212Member" id="nifi_C000015212Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000123980Member" id="nifi_C000123980Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015210Member" id="nifi_C000015210Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="C000015208Member" id="nifi_C000015208Member" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
</schema>
