Frequent Exposure of Mice to Crude Brucella abortus Proteins Down‐regulates Immune Response

Mice repeatedly immunized via the intraperitoneal route with a Brucella abortus antigen lost their ability to develop a strong in vitro lymphoproliferative response. This result correlates with a decreased tendency of the lymphoid population to produce interferon‐γ when stimulated in culture with the immunizing antigen. With respect to the humoral response, as the number of immunizations increased, the animals produced more specific immunoglobulin M and immunoglobulin G1 antibodies. It is postulated that the long‐term exposure of an animal to Brucella antigen changes the nature of the immune response from a T‐cell‐mediated response to a humoral response favouring the establishment of the disease.