Isotype specific immunoregulation: role of Fc alpha R+ T cells and IBF alpha in IgA responses.

Fc alpha receptor (Fc alpha R)+ T cell hybridomas (Th HA cells) were derived from fusion of Peyer's patch T helper cells (PP Th A cell) which preferentially select sIgA+ B cells and support IgA responses, with the R1.1 T lymphoma cell line. Expression of Fc alpha R on Th HA cells was extensively characterized by several methods, i.e., immunocytoadherence, colloidal gold-immunoelectron microscopy, FACS and ELISA. All four assays clearly demonstrated expression of Fc alpha R on Th HA cells. The use of FACS and ELISA also suggested the expression of Fc alpha R as well as the presence of lower amounts of Fc mu R on these cell lines. The significance of coexpression of Fc alpha R and Fc mu R is currently under extensive investigation in our group. Solubilized membrane fractions derived from Th HA cells were tested for the presence of Fc alpha R on ELISA and for their ability to support in vitro IgA responses. Both Fc alpha R and Fc mu R were detected in cell membrane fractions of Th HA cells. The cell membrane fraction which contained Fc alpha R, supported in vitro IgA anti-SRBC PFC responses when added to PP B cell cultures in the presence of SRBC. This activity was removed by adsorption to an IgA affinity column. On the other hand, the bound fraction contained sFc alpha R and supported IgA anti-SRBC PFC responses in PP B cell cultures, a response pattern that was similar to those obtained with IBF alpha. Taken together, these results suggest that Fc alpha R and IBF alpha are similar molecules and both exhibit functional activity.(ABSTRACT TRUNCATED AT 250 WORDS)