Modulation of antigen presentation and peptide-MHC-specific, LFA-1-dependent T cell-macrophage adhesion

Incubation of peritoneal macrophages in vitro before fixation increased their ability to present exogenous peptides to 3A9 T hybridoma cells. The enhanced level of presentation correlated with a greatly increased, peptide-specific adhesion of 3A9 cells to the macrophages, whereas peptide-independent adhesion was minimal and essentially unaltered. 3A9 cells exhibited rapid peptide-specific adhesion (plateau by 5 to 10 min) and deadhesion (complete reversal by 5 min). Peptide-specific adhesion was blocked by anti-I-A^k and anti-LFA-1. Interaction of T cell receptors and CD-4 with peptide-I-A^k complexes appeared to provide little direct contribution to the avidity of T cell-macrophage adhesion, but activated a LFA-I-mediated adhesion mechanism. In addition, anti-T cell receptor, anti-CD3, and anti-CD4 antibodies themselves activated LFA-1-dependent adhesion in the absence of peptide. Unlike the peptide-induced adhesion, this adhesion was similar for macrophages whether or not they were incubated in vitro before fixation. We conclude that the different macrophage populations supported LFA-I-mediated adhesion equally. Therefore, the enhancement of T cell stimulation observed after in vitro incubation of macrophages was due to increased peptide presentation and consequently increased triggering of LFA-I-mediated adhesion. Mechanisms may exist to regulate the effectiveness with which peptide-class II MHC complexes are displayed for T cell recognition.