Different Activation of Lymphocytes in Reaction to Babesia microti Infection in iNOS-/- and Wildtype Mice

Abstract

The reaction of lymphocyte populations, in iNOS-/- mice and wildtype control mice, to Babesia microti infection was investigated in this study. During the course of infection, in both groups of mice there was gross enlargement of the spleens but the spleen cell population decreased by 50%. At peak parasitemia iNOS-/- mice had a low lymphocyte count and on overall, a slight increase in leukocyte population in peripheral blood. On the other hand control mice showed a significant increase in leukocyte population but lymphocyte numbers remained unchanged. During infection the iNOS-/- mice had a higher percentage of B lymphocytes and CD4⁺ T cells in the spleen, compared to the control mice. In response to B. microti infection iNOS-/- mice produce less IL-4, but more IFN-γ compared to control mice. Parallel to the higher percentage of B cells, iNOS-/- mice also produced higher amounts of B. microti-specific antibodies. These results suggest that in the early stages of infection NO protects the lymphocytes against B. microti invasion and that the immune defense in iNOS-/- mice involves to a large extent humoral immune response.