Effect of depletion of L3T4+ cells on resistance to early primary infection of mice with Taenia taeniaeformis

The role of L3T4+ T lymphocytes in early primary infection with the metacestode of T. taeniaeformis was investigated by selective removal of these cells in vivo by parenteral injections with the rat monoclonal antibody (MAb) GK1.5 directed against the L3T4 molecule. Comparisons between treated and non-treated BALB/cByJ mice, normally resistant to infection with T. taeniaeformis, demonstrated that the treated mice had a greater percentage of viable parasites in the livers. Eosinophils were prominent in the region immediately surrounding parasite larvae in control mice, whereas treated mice showed virtually no eosinophil infiltration. Additionally, fewer tissue macrophages were evident near parasite larvae in the treatment group when compared to controls. The more susceptible C3H/HeDub strain mice demonstrated similar responses following treatment with the MAb, including diminished parasite killing and limited inflammatory cell infiltration. When C3H/HeDub mice were injected with the cytotoxic agent vinblastine sulfate, which has been shown to diminish Lyt-2+ suppressor cell activity, these mice remained unable to mount a strong local cellular response to the larval parasite. It is suggested that L3T4+ T lymphocytes play a crucial role in the innate resistance to T. taeniaeformis infection during the first 6 days post-infection. Effects seen following vinblastine treatment may be a result of drug-induced alterations in leukocyte chemotaxis, toxicity to other effector T cell populations, or a specific depletion of a functional Lyt-2+ T cell population that is required in addition to L3T4+ T cells for the expression of resistance to primary infection with T. taeniaeformis.