Administration of purified anti-L3T4 monoclonal antibody impairs the resistance of mice to Listeria monocytogenes infection.

Anti-L3T4 monoclonal antibody (GK1.5) treatment significantly impaired the antilisteria resistance of mice as manifested by increased recovery of listeriae from the spleens and livers of anti-L3T4-treated mice and by greater severity of damage to the liver and other organs. Anti-L3T4-treated mice demonstrated a profound decrease in their T cell-mediated responses to Listeria monocytogenes and its products; they failed to develop delayed type hypersensitivity to soluble listeria antigens in vivo, and their spleen cells proliferated poorly in response to stimulation by either mitogens or listeria antigens in vitro. Spleen cells from control listeria-infected mice produced significant amounts of gamma interferon when stimulated with listeria antigens in vitro, whereas under the same conditions spleen cells from anti-L3T4-treated listeria-infected mice failed to produce detectable gamma interferon. Anti-L3T4 treatment resulted in a slight increase in serum colony-stimulating activity as compared with control listeria-infected mice, probably as a result of the increased bacterial burden in these animals. Despite the dramatic decrease in T-cell activities, anti-L3T4-treated mice succeeded in clearing L. monocytogenes from the spleen and liver in a manner that was only slightly delayed as compared with control listeria-infected mice. In addition, anti-L3T4-treated listeria-immunized mice exhibited a moderate degree of enhanced resistance to rechallenge with L. monocytogenes, and their spleen cells were able to transfer a limited degree of antilisteria resistance to naive recipient mice. Both of these responses, however, were diminished as compared with those of control listeria-immunized mice in the same experiments. Although these observations establish a critical role for L3T4+ cells in the development of maximal resistance to listeriosis, they also suggest that compensatory mechanisms may allow mice to develop considerable antilisteria resistance even when L3T4+ cell activities are substantially reduced.