Immunoresponsiveness in acute babesiosis in humans.

Immunoresponsiveness in patients with acute babesiosis was characterized. Lymphocyte subpopulations, mononuclear cell responses to nonspecific mitogens, and serum immunochemical values were studied in patients during acute babesiosis and after recovery (four to 40 months), controls, and seropositive individuals. Serum studies were also carried out retrospectively on stored sera from patients with babesiosis. Mean and differential lymphocyte counts and percentages of B lymphocytes were higher than in controls in patients with acute babesiosis, and levels of T lymphocytes bearing the IgG Fc receptor (T gamma) were significantly (P less than 0.01) elevated. Responses to nonspecific mitogens were suppressed during acute babesiosis. Levels of serum IgG and IgM and Clq binding were significantly increased whereas C3 and C4 levels and hemolytic activity were suppressed in acute-phase sera. The apparent paradox of an increased T suppressor/cytotoxic population in the presence of evidence of increased in vivo lymphocyte function is discussed in terms of the heterogeneity of the T gamma subpopulation.