CD4 expression and function in HLA class II-specific T cells.

The CD4 molecule is currently the object of intense interest and investigation both because of its role in normal T-cell function, and because of its role in HIV infection. Our studies of CD4 expression and function on class II-specific T cells indicate that: 1) CD4 expression is generally a marker of T cells that are committed to class II antigen recognition, even when they have cytotoxic function; 2) CD4 is typically involved in the proliferative and cytotoxic function of such cells, which we hypothesized to be due to interaction with a nonpolymorphic determinant on class II; 3) the importance of CD4 to the recognition is most prominent in T-cell interactions with low "avidity"; and 4) although CD4 may play a role in adhesion per se, the majority of its function seems to be in a post-adhesion phase of cytotoxic T-cell recognition.