Background: Brucella is an intracellular bacterium that causes chronic infection in humans and domestic animals. The underlying mechanisms that cause prolonged illness are complex and not fully understood. Immune responses may have an important role in the chronicity of infection. Here, we evaluated the lymphocyte proliferation responses in patients with chronic and acute brucellosis.

Materials and Methods: This descriptive - analytical study was performed on 22 patients with acute brucellosis, 21 patients with chronic brucellosis and 21 healthy people with the similar age, sex and genetic background as control group. Peripheral lymphocytes were isolated using Ficoll and the cellular proliferation was quantified in presence of antigen and phytohemaglutinin-A by MTT method.

Results: The brucella antigen-specific stimulation index in patients with chronic brucellosis was significantly lower than the acute brucellosis patients (p=0.001). Also, stimulating the lymphocytes with phytohemaglutinin-A has shown that proliferative response in patients with chronic brucellosis was lower than the other groups (p=0.04).

Conclusion: The results indicated that chronic brucellosis inhibits lymphocyte proliferation. This inhibition of lymphocyte proliferation may be due to the induction of anergy.