Role of CD8 T cells in rat IgE responses

The role of the cytokines interleukin-4 and interferon-gamma in the regulation of IgE responses in the mouse and man have focused on the role of CD4 T cells. In the rat, antigen-specific CD8 T cells, generated following inhalation of antigen, have been shown to be capable of suppressing IgE responses. Repeated intraperitoneal injections of 1 ng ricin and 1 microgram antigen established a long-lived IgE response in both low- and high-IgE responder rat strains (Wistar and Brown Norway). The duration of the IgE antibody response was 204 and 248 days, respectively. Total IgE levels rose from 30 +/- 20 to 39,000 +/- 7,500 ng/ml in the Wistar rat and from 120 +/- 100 to 47,000 +/- 8,000 ng/ml in the Brown Norway rat. An even greater (10(4)-fold) increase was seen in antigen-specific IgE antibody levels. Ricin alone had no effect and concomitant or prior stimulation with antigen was required. The proportion of CD4+ and CD8+ cells present in the spleen at the peak of the IgE response was markedly increased compared with animals given ricin or antigen alone. Furthermore, CD8 T cells were approximately 100 times more sensitive to ricin than CD4 T cells. These data suggest that enhancement of IgE responses in ricin-treated animals results from the selective deletion of T cells which suppress IgE and are of the CD8 phenotype.