T-Cell help for the IgA response: The function of T cells from different lymphoid organs in regulating the proportions of plasma cells expressing various isotypes

Abstract

Differential distribution of IgA-specific primed Lyt 2 − T cells (T H) in favor of gut-associated lymphoid tissue (GALT) has been proposed to account for the high proportion of IgA-producing plasma cells at mucosal versus nonmucosal sites. We find, however, that GALT T H primed enterically with sheep red blood cells (SRBC) contain no more help for IgA responses than peripheral lymph node (PN) T H primed subcutaneously. Moreover, GALT T H are only poorly primed by enterically administered soluble protein antigen and therefore provide less help for all isotypes than PN T H primed subcutaneously with the same antigen. On the other hand, supernatants of GALT T H stimulated with concanavalin A (Con A) in vitro do help higher IgA:IgG plaque-forming cell (PFC) ratios in cultures with 2,4,6-trinitrophenyl-SRBC (TNP-SRBC) than supernatants from PN and spleen, indicating that, when appropriately stimulated, GALT T H are capable of promoting relatively higher IgA responses than T H from other sources. Responses elicited by either SRBC-primed T H or splenic Con A supernatants in the presence of TNP-SRBC contained higher IgA:IgG PFC ratios than those elicited by linked recognition in the presence of haptenated soluble protein carrier.