Role of delayed type hypersensitivity responses in protection during chronic Plasmodium berghei infection as evidenced by homing of radiolabelled bone marrow cells and contact sensitivity.

A comparative study of specific and non-specific immunosuppression has been carried out in acute and chronic Plasmodium berghei infected mice in an in vivo system. In our previous studies, immunosuppression during acute P. berghei infection was attributed to T lymphocytes when we studied modulation of blastogenic response of lymphocytes in an in vitro system. In the present study, delayed type hypersensitivity (DTH) was evident from the homing of radiolabelled bone marrow cells into the delayed lesions of antigen challenged foot pads during chronic infection. This response was suppressed during acute infection especially in early stages. A greater concentration of bone marrow cells in the liver and spleen occurred during chronic infection in comparison with acute infection. When radiolabelled bone marrow cells from infected mice were injected into the normal mice previously given malaria antigen in foot pads, no significant change in homing pattern in liver, spleen or foot pads was observed. Contact sensitivity to picryl chloride was suppressed during acute infection, but was intact during chronic infection. Since these responses are mediated by T lymphocytes, significance of these responses is discussed.