Activation and proliferation of T lymphocyte subpopulations in patients with brucellosis

Background. T-cell proliferation is a standard method to evaluate cellular immune responses against intracellular infectious agents. The present study was undertaken to look for expression of an early activation marker (CD69) and proliferation using a nonradioactive method to evaluate cellular immune response against a salt-extractable antigen from Brucella melitensis 16M (RCM-BM) in patients suffering from brucellosis. Methods. Expression of CD69 on membrane of CD4⁺ and CD8⁺ T-cells was determined by flow cytometry. Lymphoproliferation was determined by tritiated thymidine and 5-bromo-2′-deoxyuridine (BrdU) incorporation using liquid scintillation counter or flow cytometry, respectively, to evaluate DNA synthesis. Results. Thirty healthy donors and 24 patients suffering from brucellosis were included in this study. In all cases, incubation with mitogen induced expression of CD69 and proliferation of both CD4⁺ and CD8⁺ T-cells. In contrast, only brucellosis patients responded with expression of CD69 and proliferation against RCM-BM antigen from Brucella melitensis (p<0.001). Conclusions. Methods used in this study were useful to evaluate immune response against specific antigen or polyclonal stimulation. CD4⁺ and CD8⁺ T cells from patients became equally activated and proliferated in response to RCM-BM antigen. Our data suggest that both T-cell subpopulations play an important role in immune response against Brucella.