Studies on Immune Responses to Larval Cestodes in Mice. Immunoglobulins Associated With the Larvae of Mesocestoides Corti

Summary Hypothymic BALB/c.nu/nu (“hude”) mice were markedly more susceptible than their intact BALB/c.nu/+ littermates to infection with the murine larval cestode, Mesocestoides corti, and antigens of this parasite induced T cell‐dependent immune responses in intact mice. Defective anti‐dinitrophenol (DNP) antibody responses were induced by DNP‐M. corti larvae and DNP‐human gamma globulin (HGG) in infected (parasitized) intact mice. However, on transfer to uninfected irradiated recipients, lymphoid cells from infected intact mice responded well to DNP‐M. corti larvae. By using washed peritoneal larvae from long term infected intact mice to absorb antisera directed against various Ig classes and IgG subclasses, and by analysis of acid eluates of such living larvae, large amounts of IgG1, lower amounts of IgM, trace amounts of IgG2 and IgG3 and no IgA immunoglobulins were found to be associated with the larvae. In the case of nu/nu derived larvae, IgM immunoglobulins predominated. Chronically infected intact mice contained large amounts of IgG1, immunoglobulins in their serum. The technique of lactoperoxidase‐catalysed radioiodination revealed that very few proteins were available for labelling on peritoneal larvae under conditions used for labelling of lymphoid cell surface molecules. In fact, proteins with Ig chain mobilities accounted for much of the labelled and extracted proteins detected by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE). Patterns of labelled and extracted proteins from nu/nu derived larvae were even simpler and no clear protein peaks were detected consistently in material from labelled, acid treated, nu/nu derived larvae. Evidence is presented that at least the IgG1 molecules associated with M. corti larvae from long term infected mice include antiparasite antibodies. Immunoglobulins associated with M. corti larvae in long term infected mice are most unlikely to be useful to the mouse in terms of preventing parasite establishment (in secondary murine hosts) or reducing the proliferative rate of larvae. However, no clear cut evidence is as yet available to answer the question of whether the M. corti associated Ig (and, in particular, IgG1 which is reported to be relatively inert with respect to direct pathogenic effects) serves the function of masking parasite antigens and protecting the established parasites from more aggressive T cell‐dependent immunological effector mechanisms.