Specific unresponsiveness to sheep red blood cells visualized by levamisole in athymic nude mice.

The administration of levamisole at the time of and 2 days after challenge with 10(8) SRBC significantly increased the direct anti-SRBC PFC response of nude mice. Pretreatment of nude mice of BALB/c and C 57 B1/10Sn strains with 10(9) or 10(8) SRBC injected 14 and 7 days before challenge suppressed the increase of the immune response. Pretreatment with 10(7) SRBC did not induce this inhibition. Administration of levamisole at the time of pretreatment with SRBC did not prevent the induction of inhibition. It is suggested that B cell exhaustion is the cause of the observed unresponsiveness.