Induction of an immune response in athymic nude mice to thymus-dependent antigens by Pseudomonas aeruginosa exotoxin A.

Exposure of spleen cells from athymic nude mice to Pseudomonas aeruginosa exotoxin A induces these cells to respond to the thymus-dependent (TD) antigen sheep erythrocytes (SRBC). The response induced by toxin is dose dependent, antigen specific, and not due to polyclonal B-cell activation. Enhancement of the anti-SRBC response can be observed when toxin addition precedes antigen stimulation by 24-48 hr, which decreases when toxin administration follows antigen stimulation. A significant response is also observed when toxin and antigen are added simultaneously. A significant anti-SRBC response can be observed out to Day 10 postantigen and toxin stimulation after attaining a peak response at Day 5. Cultures exposed to toxin in the presence or absence of antigen exhibited a higher cell number and relative number of B cells as compared to control cultures. Exposure of T-cell depleted B cells from euthymic +/nu mice to toxin plus antigen does not result in an anti-SRBC response indicating that exotoxin A alone is not sufficient to induce B-cell responsiveness to T-dependent antigens and that other cells and/or factors are involved in the toxin-induced responsiveness of nude mice to T-dependent antigens.