Characteristics of the immune response during acute brucellosis in Sprague-Dawley rats.

Background: Brucella is a facultative, intracellular pathogen that causes severe disease in animals and humans. Immunity against Brucella involves both humoral and cellular responses. To investigate the characteristics of immune response in acute brucellosis in Sprague-Dawley (SD) rats, IgG and its subclass specific immunoglobulins' (IgG1 and IgG2a) response in sera against B. abortus biotype 1 infection were studied. Methodology: Thirty-six rats were inoculated intraperitoneally with 0.1 ml apyrogenic saline containing 1 x 10(10) colony forming unit (CFU) of B. abortus biotype 1 Korean bovine isolate. Four rats were used as uninfected controls. The sera were collected from infected rats at 3, 7, 14, 21, 28, 35, 42, 49, and 56 days post infection (DPI) and screened for Brucella specific antibody response by the rose bengal plate test (RBPT). IgG and its subclass specific immunoglobulins' (IgG1 and IgG2a) response in the sera were measured by a lipopolysaccharide (LPS) based indirect enzyme-linked immunosorbent assay (IELISA). Results: Brucella specific IgG, IgG1 and IgG2a responses in the sera of infected rats were detected from 3 DPI by IELISA. IgG and IgG1 concentrations in sera reached the peak level at 35 DPI, and then the concentrations gradually declined to the end of the experiment. IgG2a concentrations in the sera remained almost constant from 7 DPI until the end of this study. Conclusion: In acute brucellosis, IgG2a response (indicative of a Th1 response) was found to be significantly dominant over IgG1 response (indicative of Th2 response) (P < 0.001).