Immune response modulation by colonization of germfree rats with Propionibacterium acnes.

Propionibacterium acnes (oral and/or parenteral administration) had a modulating effect on antibody-and cell-mediated immune responses of germfree (GF) and monoassociated (MA) rats. In conventionally reared rodents, parenteral injection of killed P. acnes stimulated the splenic plaque-forming cell response to sheep erythrocytes. However, in GF rats and in rats monoassociated with viable P. acnes, parenteral injection of killed P. acnes antigen inhibited the plaque-forming cell response to sheep erythrocytes. When compared with the responses of GF control rats, splenocytes from GF rats parenterally injected with P. acnes antigen had a decreased in vitro blastogenic response to phytohemagglutinin and concanavalin A and an increased blastogenic response to homologous bacterial antigens. Conversely, a parenteral injection of P. acnes antigen into P. acnes MA rats resulted in an increased splenocyte blastogenic response to phytohemagglutinin and concanavalin A but not to homologous (P. acnes) antigens. Thus the presence or absence of intestinal antigenic stimuli (in MA and GF rats) had a modulating effect on the immune response to a parenteral injection of P. acnes antigen.