cluster of differentiation 4 (CD4)

clus·ter of dif·fer·en·ti·a·tion 4 (CD4)

(klŭs'tĕr dif'ĕr-en-shē-ā'shŭn) A glycoprotein found on various subsets of T cells, i.e., usually on helper and some T-cytotoxic cells.