A study of humoral and cellular immunity in the bovine chronically infected with Brucella abortus

Abstract

Enzyme-linked immunosorbent assays (ELISA) were designed or modified for the in vitro detection of anti-Brucella abortus antibodies (class and subclass), free B. abortus antigens, B. abortus-anti-B. abortus immune complexes (Cl1-ELISA) and B. abortus antigens dissociated by low pH dialysis from B. abortus-anti-B. abortus complexes. The assays were adequate for detecting low concentrations of antibody, antigen (0.75 [mu]g), complexes (20 [mu]g). Infected and exposed animals of the Texas A&M University brucellosis experimental herd and field herds did not have sufficient concentrations of free antigen or immune complexes in their sera for these assays to be of diagnostic significance in this study. The frequency of chronic brucellosis as defined by the absence of a diagnostic antibody titer by the card, Rivanol, tube and complement fixation tests (conventional assays) was high. On a bleeding date 11 months after initial exposure to virulent B. abortus, 2 principals of the experimental herd were diagnosed as being acutely infected with B. abortus by conventional assays. The standard and Rivanol ELISA's identified 8 animals which had diagnostic concentrations of IgG antibody, specifically IgG1, indicative of persistent antigen exposure and acute infection. The animals, positive by the standard ELISA and not detected by the conventional assays, were therefore, considered chronically infected with B. abortus. The standard ELISA for detecting antibody activity was determined to be a sensitive and efficient assay for identifying animals with possible chronic infections and the potential to spread the disease to healthy animals. An inhibitor(s) of human Clq binding of aggregated bovine IgG was discovered during the development of the solid phase human Clq ELISA for immune complexes. It is suggested that the inhibitor(s) may have an in vivo biologic and potential therapeutic significance. Brucella abortus antigens and B. abortus-anti-B. abortus synthetic immune complexes were found to suppress pokeweed mitogen (PWM) induced stimulation of bovine lymphocytes. Antigens appeared to be toxic to lymphocytes at high concentrations, and a regulatory mechanism of suppression of PWM induced stimulation of bovine lymphocytes was apparent at low concentrations of antigens...