T lymphocytes that contribute to the immunoregulation of granuloma formation in chronic murine schistosomiasis.

Immunoregulation of Schistosoma mansoni egg-induced granuloma formation in the mouse occurs as chronic infection is being established. Three different modes of manipulation that are known to affect immuno-regulatory T lymphocytes were applied to this model. Adult thymectomy (AdTx) of CBA/J mice, 6 wk after infection, did not affect the size of their granulomas at 8 or 12 wk after infection. However, by 15 wk after infection, sham-treated mice exhibited continued development of modulation of their granulomas, whereas AdTx mice did not. Hemagglutinating antibody titers against soluble egg antigen preparation were marginally elevated in the AdTx group. Adoptive transfer of the suppressor effect of chronic spleen cells was ablated by AdTx. In vivo administration of 1 ml of rabbit anti-mouse thymocyte serum (RAMTS) over a 3-day period to chronically infected mice resulted in a minimal increase in granuloma formation. This treatment was seen, however, to be efficacious in eliminating the suppression normally associated with adoptive transfer of chronic spleen cells. Hydrocortisone acetate (HyC) treatment of chronically infected mice (5.0 to 7.5 mg per mouse over 3 to 5 days) significantly decreased the size of their granulomas. This diminution may be due to the eosinophil-depleting activity of HyC. Adoptive transfer studies demonstrated that the granuloma suppressor mechanism was HyC-sensitive. A continuing supply of newly developed T lymphocytes appears to be required for the establishment and maintenance of a substantial portion of this immunoregulatory process in chronic infection.