Levamisole: potentiation of primary immunoglobulin M antibody responses in suckling rats

The influence of levamisole (LMS) on the primary immunoglobulin M (IgM antibody response of suckling rats was investigated. Although suckling rats did make a direct plaque-forming cell (PFC) response to sheep red blood cells (SRBC), the magnitude of this response was much lower than that of adult rats. LMS treatment (2.5 mg/kg) markedly potentiated the anti-SRBC response in 10-day-old rats, but this enhanced PFC response never attained adult levels. In contrast, LMS failed to boost the anti-SRBC response of adult rats, although the adult response to suboptimal antigenic stimuli was enhanced. The ontogeny of immunological responsiveness to SRBC was not influenced by LMS; only existing responses could be modulated. The potentiating effect of LMS was dose-dependent, with high doses causing suppression. The influence of LMS did not involve the earlier appearance of PFC. Since LMS augmented the PFC response to SRBC when administered before or after antigen, it appears that both the inductive phase and the proliferative phase of antibody production can be modulated. Finally, the PFC responses to a more thymus-independent antigen (2,4,6-trinitrophenyl-Ficoll) was boosted, suggesting that LMS may be capable of directly influencing B lymphocytes. These findings indicate that the functional immunodeficiency of the neonatal antibody response can be improved by LMS treatment.