A method for the induction of a prolonged elevated IgM response without the formation of IgG antibody, by injecting carrageenan-treated mice with multiple doses of sheep erythrocytes.

Carrageenan, a known macrophage toxin and immunosuppressive agent, has been studied for its effect on antibody responses following single doses or multiple daily increasing doses of sheep red blood cells (SRBC) injected intraperitoneally (i.p.) in male CBA strain mice. Results showed that lambda carrageenan administered prior to a single i.p. injection of SRBC markedly suppressed both the IgM and IgG responses. However, when carrageenan-treated mice were injected with multiple daily increasing amounts of SRCB antigen, high titers of specific antibody activities were produced in serum while only IgM plaque-forming cells (PFC) were detected in the spleens up to 8 weeks later. Higher serum titers were obtained if Bordetella pertussis vaccine was administered i.p. shortly before the first antigen dose was injected in the carrageenan-treated mice. Direct PFC (IgM) but not indirect PFC (IgG) were detected in suspensions of spleen cells late in the response of these mice. Such treatment may provide a useful method for raising high titers of cytotoxic IgM antibody to other T-dependent antigens. Evidence is presented to show that pertussis vaccine--a known potentiator of the IgG response--does not reverse the inhibitory effects of carrageenan. Results also provide evidence for the requirement of functional macrophages in the induction of helper-cell activity for the thymus dependent IgG response in vivo.