Frequent exposure of mice to crude Brucella abortus proteins down-regulates immune response

Mice repeatedly immunized via the intraperitoneal route with a Brucella abo rtus antigen lost their ability to develop a strong in vitro lymphoprolifer ative response. This result correlates with a decreased tendency of the lym phoid population to produce interferon-gamma when stimulated in culture wit h the immunizing antigen. With respect to the humoral response, as the numb er of immunizations increased, the animals produced more specific immunoglo bulin M and immunoglobulin G1 antibodies. It is postulated that the long-te rm exposure of an animal to Brucella antigen changes the nature of the immu ne response from a T-cell-mediated response to a humoral response favouring the establishment of the disease.