O [[HIVVIH-1]] usesutiliza o CD4 topara gainintroducirse entrydentro intodas hostcélulas T-cellsand[[hospede]]s achievesao thisunirse bya bindingel topola theproteína [[viral envelopegp120]] protein known asda [[gp120envoltura viral]].<ref name="pmid9641677">{{cite journal | author = Kwong PD, Wyatt R, Robinson J, Sweet RW, Sodroski J, Hendrickson WA | title = Structure of an HIV gp120 envelope glycoprotein in complex with the CD4 receptor and a neutralizing human antibody | journal = Nature | volume = 393 | issue = 6686 | pages = 648–59 | year = 1998 | month = June | pmid = 9641677 | doi = 10.1038/31405 }}</ref> TheA bindingunión toao CD4 createscrea aun shiftcambio inna theconformación conformation ofda gp120 allowingque HIV-1lle topermite bindao to a coVIH-receptor1 expressedunirse onao thecorreceptor hostexpresado cell.na Thesecélula co-receptorshóspede arechamado [[chemokinereceptor de receptorsquimocina]] [[CCR5]] orou [[CXCR4]]. FollowingDespois adun structuralcambio changeestrutural innoutra anotherproteína viral protein (a [[gp41]]), o HIV insertsinserta aun [[fusionpéptido peptidede fusión]] intona thecélula hosthóspede cellque thatfai allowsque thea outermembrana membraneexterna of thedo virus tose fusefusione with thecoa [[cellmembrana membraneplasmática]] celular.
=== HIVPatoloxía pathologydo VIH ===
HIVA infectioninfección leadspor toVIH ainfection progressiveproduce reductionunha inprogresiva theredución numberdo ofnúmero de [[célula T helper cellsaxudante|células T cells expressingaxudantes CD4+]]. MedicalO professionalsreconto referde toCD4 theutilízase CD4para countdecidir tocando decidese whenempeza too begintratamento treatmentdurante duringa HIVinfección por VIH e posteriormente para infectionavaliar a eficacia do tratamento. NormalOs [[bloodvalores values]]sanguíneos arenormais usuallyexprésanse expressedxeralmente ascomo theo numbernúmero ofde cellscélulas perpor microlitermicrolitro (orou cubicmilímetro millimetercúbico, mm<sup>3</sup>) ofde bloodsangue, withcon normalvalores valuesnormais forpara as células CD4 cellsde beingentre 500- e 1200 cellscélulas/mm<sup>3</sup>.<ref name="pmid1349272">{{cite journal | author = Bofill M, Janossy G, Lee CA, MacDonald-Burns D, Phillips AN, Sabin C, Timms A, Johnson MA, Kernoff PB | title = Laboratory control values for CD4 and CD8 T lymphocytes. Implications for HIV-1 diagnosis | journal = Clin. Exp. Immunol. | volume = 88 | issue = 2 | pages = 243–52 | year = 1992 | month = May | pmid = 1349272 | pmc = 1554313 | doi = | url = }}</ref> AUn reconto de CD4 countmide measureso thenúmero numberde ofcélulas T cellsque expressingexpresan o CD4., Whileque CD4serve countspara areavaliar noto aestado directdo [[HIV]]sistema test--e.g. theyinmunitario do notpaciente, checkaínda theque presencenon ofmide viraldirectamente DNA,a orcantidade specificde antibodiesvirus against(por HIV--theyexemplo, area usedpresenza tode assessADN theviral, immuneou systemde of[[anticorpo]]s aespecíficos contra patiento virus). PatientsXeralmente ofteno undergotratamento treatmentscomeza whencando theos recontos de CD4 counts reachchegan a level of 350 cellscélulas perpor microliter;microlitro less(con thanvalores 200de cellsmenos perde microliter200 inconsidérase anque HIV-positiveo individualindividuo isinfectado diagnosed asten [[AIDS]SIDA]). Medical professionals also refer to CD4 tests to determine efficacy of treatment.
[[FileFicheiro:Reference ranges for blood tests - white blood cells.png|thumb|500px|center|[[ReferenceRangos rangesde forreferencia bloodpara testsanálises de sangue]] ofde whiteglóbulos blood cellsbrancos, comparingonde se compara a cantidade de células CD4+ cell(mostradas amounten (shownamarelo in green-yellowverdoso) withcon otheroutras cellscélulas.]]
