The fine structure of sarcoid and tuberculous granulomas

Summary The granulomas of sarcoidosis and non-caseating tuberculosis show similar cell-types: two forms of epithelioid cells, A and B, giant cells, lymphocytes and ‘activated’ mononuclear cells. The morphology of epithelioid cells suggests that they are primarily biosynthetic rather than phagocytic. The relationship of these various cells to each other is discussed and the following sequence of granuloma development is suggested: circulating lymphocyte → activated mononuclears → A → B epithelioid cell whose secretory product stimulates transformation of other circulating lymphocytes.