LATERAL DYNAMICS OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-II MOLECULES BOUND WITH AGONIST PEPTIDE OR ALTERED PEPTIDE LIGANDS

We examined the lateral diffusion of I-A(d) on A20 cells following the binding of ovalbumin-derived peptides. The peptides were OVA(323-339) and OVA(325-335) and a related peptide OVA(325-335S) substituted H331 Q. Only OVA(323-339) and OVA(325-335) were effectively presented by A2 0 cells to DO-11.10/S4.4 T cells as assessed by IL-2 production. Fluor escence photobleaching recovery (FPR) measurements showed anti-I-A(d) to have a lateral diffusion coefficient on untreated A20 cells of 1.8 +/- 1.0 x 10(-10) cm(2) s(-1) at 25 degrees C with fluorescence recove ry after photobleaching greater than 50%. After 24 h incubation of A20 cells with OVA(323-339) or OVA(325-335), a subpopulation of A20 cells appeared that were approximately half the size of untreated A20 cells . Culture of A20 with OVA(325-355S) did not stimulate DO-11.10 cells o r induce a size change in A20 cells. Class II molecules were laterally immobile on these small cells with fluorescence recoveries after phot obleaching of less than 20%. The relative number of small cells in the A20 cell population was correlated with the immunogenicity of the pep tides. These results suggest that immobilization of surface I-Ad may b e an important event in antigen presentation.