T cell proliferation is a standard method to evaluate cellular immune responses against intracellular infectious agents. Recently, intracellular cytokine assay is a valuable procedure for studying of the immune response to various stimuli such as intracellular microbes. The present study was undertaken to assess cell-mediated
   immune responses in patients with acute and chronic brucellosis.

          Diluted whole blood samples of patients with acute (n=14) and chronic brucellosis (n=13) with age 35.33± 21 years, and sex and age-matched healthy volunteers(n=22) were cultured in the presence of either mitogen; heat inactivated bacteria or medium alone. Intracellular IFN-γ expression in CD3⁺ cells was detected
   by flow cytometry. Lymphoproliferation was determined by titiated thymidine incorporation using scintillation counter, to evaluate DNA synthesis.

          In all groups, incubation with mitogen induced proliferation of lymphocytes and intracellular IFN-&gamma; expression of CD3⁺ cells. In contrast, only brucellosis patients responded with cell proliferation and IFN-&gamma; production against heat killedBrucella melitensis. However, blastogenic responses and IFN-&gamma;-producing CD3⁺ cells were significantly decreased in response to antigen in chronic group compared to patients with acute brucellosis of patients (P<0.001). There was a close correlation between the number IFN-g- producing CD3⁺ cells only in acute group which shown polarization of immune responses to Th1 type.

          Methods used in this study were useful to evaluate immune responses against specific antigen or polyclonal stimulation. Our data was shown patients with acute infection responded to Brucella antigens by IFN-g expression and proliferation and induced production of T helper 1 (Th1) cytokines, whereas chronically infected patients do not.