In situ analysis of cytokine responses in experimental murine schistosomiasis.
BACKGROUND: Infection with schistosomiasis results in CD4+ T helper (Th) cell-dependent granulomatous inflammation around parasite eggs. T cell-derived cytokines play a critical role in the induction and subsequent down-modulation of the granulomas. These cytokine responses have been previously examined in lymphoid cell supernatants or in tissue homogenates but have not been examined directly in the local microenvironment of the lesions or in the reacting lymphoid tissues. EXPERIMENTAL DESIGN: With the use of specific mAb, the cytokines IL-2, IFN gamma, IL-4, and IL-10 were investigated by direct immunocytochemical analysis in situ in hepatic egg granulomas and lymphoid organs from acutely and chronically infected mice. Cytokine expression in situ was compared with cytokine production during a secondary response in vitro. RESULTS: All cytokines examined were detected in various amounts in both the hepatic egg granulomas as well as in mesenteric lymph nodes and spleen. The majority of cells expressing the cytokines was found in lymph nodes, and very few were found in granulomas. Relatively small numbers of granulomas contained most of the cytokine-expressing cells, which tended to localize in their periphery. Granulomas and lymphoid organs in the acute disease contained significantly more cytokine-expressing cells in comparison with those from the chronic disease. This observation correlated well with cytokine production in vitro. CONCLUSIONS: Direct immunocytochemical examination in situ was used to detect and measure cytokine-producing cells in hepatic egg granulomas and reacting lymphoid organs of acute and chronic experimental murine schistosomiasis. Observed cytokine patterns suggest that granulomas contain T lymphocytes of both the Th-1 and Th-2 types and that cytokine production occurs during a limited time in the early granuloma. The immunocytochemical technique affords a direct appraisal of amount, dynamics, and localization of cytokine-producing cells in the unperturbed local environment.