Binding of bacteria from the genus Brucella to human B lymphocytes

In previous studies, we have shown that various lymphocyte subpopulations bind different strains of bacteria of different genera and species. Among these bacteria was a strain of Brucella melitensis which bound to all human B lymphocytes. To determine whether the binding of B. melitensis to human B lymphocytes was strain, species, or genus characteristic, we tested the binding of B. melitensis, Brucella abortus, Brucella ovis, Brucella suis, Brucella canis and Brucella neotomae to human normal and leukemic B lymphocytes. The binding of different Brucella species to B lymphocytes was determined by single- and double-labeling experiments in which a strain of Escherichia coli, coated with anti-light chain antibodies, was used as a marker for B cells. As in previous experiments, we found that B. melitensis and antibody-coated E. coli bound to the same cells. Also, we found that all the other species of bacteria tested bound to the B lymphocytes, normal or leukemic. B. ovis and B. neotomae, which are not human pathogens, bound to fewer B lymphocytes than did the human pathogens B. abortus, B. melitensis, B. suis, and B. canis. Furthermore, we found that the quality of rosettes formed by the nonpathogenic bacteria with the lymphocytes, i.e., the number of bacteria per lymphocytes, was lower than that of pathogenic Brucella species. We conclude that all of the Brucella species tested have the ability to bind to human B lymphocytes, but that only those which are human pathogens bind firmly to all B lymphocytes and may be used as reliable markers for these cells. We also suggest that the binding of Brucella species to B lymphocytes may have some bearing on the pathogenesis of brucellosis in humans.