Depression of contact sensitivity and enhancement of antibody response in Pseudomonas aeruginosa-infected mice.

The effect of Pseudomonas aeruginosa infection on contact sensitivity to 2-phenyl-4-ethoximethylene-oxazolone (oxazolone) and on antibody response to sheep erythrocytes, horse erythrocytes, and Escherichia coli 0111:B4 lipopolysacharide was investigated in outbred C57BL/6 mice. Injection of 0.5 and 0.2 median lethal doses significantly depressed contact sensitivity to oxazolone, whereas injection of 0.5 median lethal dose of heat-killed microorganisms did not. The filtrate of a 24-h broth culture did not affect contact sensitivity as well. Antibody production against sheep erythrocytes, horse erythrocytes, and lipopolysaccharide (evaluated as plaque-forming cells and circulating hemagglutinin and hemolysin titers) was found to be significantly enhanced both in animals injected with living bacteria and in those which received heat-killed microorganisms. The simultaneous occurrence of depression of cell-mediated immunity and potentiation of humoral response suggests that P. aeruginosa might interfere at different levels of the host immunological responsiveness.