The enhancing effect of mitogens on the in vivo immune response of rabbits

The effect of Con A and PHA on the primary humoral immune response in rabbits was investigated and compared with the effect of LPS and irradiation. Both Con A and PHA enhanced PFC levels and precipitating antibody titers to HuIgG when injected simultaneously with AHuIgG. Comparable enhancement of the response to HuIgG was obtained by simultaneous injection of LPS with AHuIgG or by irradiating rabbits (500 R) 24 hr after injection of the antigen. Further studies with Con A showed that its adjuvant effect was not restricted to a particular antigen since it also enhanced antibody responses to both SRBC and Bov Tg when injected simultaneously with either of these antigens. Although optimal enhancement of the response to HuIgG occurred when antigen and mitogen were injected simultaneously, some enhancement was obtained if Con A was injected 2 days after antigen, whereas the response was decreased if Con A was injected 2 days before antigen. Splenic PFC in A/J mice injected with doses of AHuIgG and Con A equivalent on a body weight basis to those used in rabbits were also enhanced by simultaneous injection of Con A with the antigen.