Human T lymphocytes expressing the C3b/C4b complement receptor type one (CR1, CD35) belong to Fc gamma receptor-positive CD4-positive T cells.

The phenotypic characteristics of human T lymphocytes expressing the C3b/C4b complement receptor type one (CR1, CD35) were investigated using dual-color surface immunofluorescence and cytofluorometric analysis of stained peripheral blood mononuclear cells (PBMC) from normal individuals. Two to ten percent of PBMC coexpressed CR1 and the CD5, CD2, or CD3 antigen. CR1 was detected on a subset of CD4+ T lymphocytes but not on CD8+ or on Leu-7+ lymphocytes. Costaining for CR1 and for the CD4 subpopulation markers anti-Leu-8, TQ1, OKT17, 2H4, and 4B4 indicated that CR1 on lymphocytes may be coexpressed with any of these phenotypic determinants. All CR1+ lymphocytes expressed Fc gamma receptors (Fc gamma Rs) as assessed by their ability to bind biotinylated dimeric human IgG. The expression of CR1 was increased in mixed lymphocyte reaction with kinetics similar to those of HLA-DR antigen expression. Coexpression of CR1 and Fc gamma R+ may provide a subset of CD4+ lymphocytes with an enhanced ability to bind and respond to C3-bearing complexes of IgG and antigen.