Interactions of the mast cell function-associated antigen with the type I Fcε receptor

Abstract

Clustering the mast cell function-associated antigen (MAFA), a membrane glycoprotein expressed on 2H3 cells, by its specific monoclonal antibody G63 substantially inhibits secretion normally triggered by aggregating these cells’ Type I Fcε receptor (FcεRI). To explore possible MAFA-FcεRI interactions giving rise to this inhibition, we have studied by time-resolved phosphorescence anisotropy the rotational behavior of both MAFA and FcεRI as ligated by various reagents involved in FcεRI-induced degranulation and MAFA-mediated inhibition thereof. From 4 to 37 °C the rotational correlation times (mean±S.D.) of FcεRI-bound, erythrosin-conjugated IgE resemble those observed for MAFA-bound erythrosin-conjugated G63 Fab, 82±17 μs and 79±31 μs at 4 °C, respectively. Clustering the FcεRI-IgE complex by antigen or by anti-IgE increases the phosphorescence anisotropy of G63 Fab and slows its rotational relaxation. Lateral diffusion of G63 Fab is also slowed by antigen clustering of the receptor. Taken together, these results suggest that unperturbed MAFA associates with clustered FcεRI. They are also consistent with its interaction with the isolated receptor, a situation also suggested by FRET measurements on the system.