Antigen cap formation in cultured fibroblasts: a reflection of membrane fluidity and of cell motility.

Reaction of antibody to surface Histocompatibility-2 antigens of cultured mouse fibroblasts causes aggregation of the cellular antigens into caps; these appear as areas of high antigen concentration localized away from the cell processes. Cap formation is inhibited when ATP generation by cells is interrupted, when the temperature is lowered, by addition of cycloheximide-especially over long time periods-and by colcemid. The observations are consistent with a role of the locomotor system of cells in the collection of small antigen-antibody aggregates into a large localized cap. Together with observations on the absence of caps in epithelial cells, these findings suggest that only cells, such as fibroblasts and lymphocytes, that bear leading ruffled membranes are capable of driving antigenantibody aggregates to form caps.