Immune response to Listeria monocytogenes in rabbits and humans.

Rabbits were immunized with listeria antigens, staphylococcus antigen, or with both, and the course of their immune response was monitored. Antibodies to Listeria and Staphylococcus were produced in both immunoglobulin M (IgM) and immunoglobulin G (IgG) classes in response to inoculation with the specific antigen. Cross-responses occurred in rabbits injected only with Listeria or only with Staphylococcus, as well as in rabbits injected with both antigens. L. monocytogenes serotype 4d appeared to be immunologically distinct from L. monocytogenes serotype 2 and its cross-reaction with S. aureus. Human sera from bacteriologically confirmed cases of listeriosis were examined to determine the nature of the immunological response of man to Listeria. In the sera studied, IgM was the predominant antibody produced to Listeria, whereas cross-reactions with Staphylococcus were observed in both the IgM and the IgG antibody classes.