Numerical and functional alterations of lymphocytes in human schistosomiasis

Peripheral blood mononuclear cells from 29 Sudanese children heavily infected with Schistosoma haematobium and S. mansoni were examined for lymphocyte subpopulations, for mitogen responsiveness in the absence and presence of interleukin-2 (IL-2), and for natural killer (NK) cell activity. The nutritional status was assessed by anthropometric and biochemical measurements. In comparison with a group of healthy Caucasian individuals the children with schistosomiasis showed a profound alteration of their cellular immune variables, reflecting a severe acquired immunodeficiency syndrome. The T-cell compartment, in particular the OKT4+ helper/inducer subset, was numerically reduced at the expense of an increased B-cell compartment. The patients' OKT4/OKT8 ratios were significantly diminished (median, 1.2; 95% confidence limits, 0.8-1.7) corresponding to a decreased responsiveness to the T-cell mitogen concanavalin A. Since addition of exogeneous IL-2 significantly enhanced the patients' lymphocyte proliferation in response to Con A, a defective IL-2 production was assumed to be at the origin of the impaired mitogenic response in chronic schistosomiasis. With regard to NK cell activity, most patients' lymphocytes failed to mediate significant cytotoxicity against the K562 target cell line, although normal percentages of cells with the NK phenotype (HNK-1+) were present. The results are discussed in view of immunological alterations seen in other parasitic infections with a heavy parasitic load.