Functional depletion of T- and B-memory cells and other lymphoid cell subpopulations-during trypanosomiasis.

T. brucei infection in mice causes generalized immunosuppression with multiple changes in the cells of the lymphoid tissue. Loss of B cell responsiveness to antigens and mitogens, and the induction of suppressive T-cells and macrophages, have been previously reported (Hudson, Byner, Freeman & Terry, 1976; Corsini, Clayton, Askonas & Ogilvie, 1977; Jayawardena & Waksman, 1977). In this study, purified B- or T-cell populations from infected mice have been tested functionally in vitro or in vivo by transfer into syngeneic irradiated hosts to separate the cells from trypanosomes or their products. B-memory cells for thymus dependent (DNP-KLH) and thymus independent (DNP-Ficoll) antigens are depleted or lose their potential to respond to the antigen during T. brucei infection. Similarly, purified T-helper cells, and T-cells reactive to allogeneic target cells in mixed lymphocyte reactions are functionally defective. By 16 days of infection all these responses are less than 10% of the normal level. The loss of B-cell function follows the peak parasitaemia and is accompanied by increases in the serum levels of both IgM and IgG. Enhanced Ig production and decline in B-cell potential also occur in T-deprived mice and in CBA/N mice which lack a subset of T-independent B-cells. Cells affecting delayed hypersensitivity reactions retain their activity throughout trypanosome infection and so far provide the only exception to the general decline in immune potential.