REGULATION OF T-HELPER-B-LYMPHOCYTE ADHESION THROUGH CD4-HLA CLASS-II INTERACTION

Abstract

Antigen‐independent adhesion of CD4+ T lymphocytes to Epstein‐Barr virus (EBV)‐transformed B cells is mediated by CD2/lymphocyte function‐associated antigen (LFA)‐3 and LFA‐1/intracellular adhesion molecule (ICAM)‐1. Although some anti‐CD4 antibodies block the antigen‐independent adhesion of CD4+ T lymphocytes, the CD4‐HLA class II interaction does not appear to significantly contribute to the forces of cell adhesion since CD4+ T cells equally bind HLA class II+ and HLA class II− mutant B cells. In addition, conjugates formed between CD4+ T cells and HLA class II− B cells remain stable for at least 1 h while CD4+T/HLA class II+ B cell conjugate percentages promptly drop off. Down‐regulation of CD4 or spontaneous low expression of CD4 also results in a persistance of conjugates formed with B cells. The role of the CD4‐HLA class II interaction has been further studied by investigating the inhibitory effect of synthetic 12‐mer peptides analogous to HLA class II and containing the Arg‐Phe‐Asp‐Ser sequence conserved in the β1 domain. These peptides were previously found to inhibit HLA class II‐restricted T cell responses, this sequence being thought to be involved in CD4‐HLA class II interaction. These peptides block conjugate formation of CD4+ resting T cells or clones but not of CD8+ T cells, by interacting with the T cells as shown by preincubation experiments. Down‐regulation of CD4 or spontaneous low expression results in the loss of the inhibitory activity. The peptide‐mediated inhibition is neutralized by a soluble dimeric CD4 molecule. Alteration within the Arg‐Phe‐Asp‐Ser sequence results in a significant loss of inhibition. It is thus proposed that the CD4‐HLA class II interaction negatively regulates antigen‐independent adhesion of T cells, this interaction involving the highly conserved Arg‐Phe‐Asp‐Ser sequence in the HLA class II β1 sequence as a CD4‐binding site.