= Chemokine receptor
A \b[chemokine receptor] is a cell-surface <receptor> that recognizes a <chemokine>. Conventional <chemokine receptors> couple ligand recognition to <G protein> signaling, often helping <leukocytes> respond to spatial chemical cues. A <chemokine receptor> should not be confused with the secreted <chemokine> that binds it. The wider family includes atypical members whose signaling and ligand-handling properties require separate description.https://www.guidetopharmacology.org/GRAC/FamilyIntroductionForward?familyId=14[IUPHAR/BPS originating receptor-family introduction: chemokines and seven-transmembrane receptor signaling]{ref}
An important experimental example is a receptor being used for a purpose beyond its normal signaling role. <H. Deng> and colleagues reported that the receptor then called CC-CKR-5, now <CCR5>, provided a principal entry cofactor for the envelope proteins of primary macrophage-tropic <HIV-1> strains. <CD4> alone did not account for the entry requirements, and the result differed from the cofactor used by the tested T-cell-line-adapted viruses.<Identification of a major co-receptor for primary isolates of HIV-1 by H. Deng and others>[Nature 381,661–666(1996), abstract: entry cofactors and strain-context distinction.]{ref}
This illustrates why binding, signaling and viral entry must be distinguished. A cell might express <CD4> yet lack a compatible additional entry factor; conversely, detecting a <chemokine receptor> does not demonstrate infection. A receptor-expression comparison can therefore test an entry requirement without establishing that every virus strain uses the same receptor. In migration experiments, receptor expression likewise does not by itself measure the direction, speed or persistence of cell movement.
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