Bronchoalveolar cells from sarcoid patients demonstrate enhanced antigen presentation

The recognition of foreign antigens by T lymphocytes in association with lung antigen-presenting cells may be critical in the initiation of the mononuclear alveolitis and granuloma formation of pulmonary sarcoidosis. However, it has been shown that bronchoalveolar cells (BAC) from normal volunteers function poorly as antigen-presenting cells. Therefore, the ability of sarcoid BAC to serve as accessory cells for antigen-dependent autologous T cell proliferation, as measured by tritiated thymidine uptake, was compared with that of normal BAC. Although irradiated sarcoid BAC supported antigen-induced T cell proliferation, normal BAC did so poorly (p less than 0.005). Because it has been shown that sarcoid BAC produce more interleukin 1 (IL 1) than normal BAC, it was considered that the enhancement of antigen-induced proliferative responses could result from an increased amount of IL 1, and that contaminating monocytes in the peripheral blood T cell preparations displayed the antigen for T cell recognition. Therefore, it was necessary to establish that antigen-induced T cell responses required HLA-D region compatibility between the sarcoid BAC and T lymphocytes. BAC from sarcoid patients stimulated antigen-specific proliferation in T cells lines matched for at least one HLA-D-region antigen, but failed to stimulate T cell lines that were unmatched for both antigens. This finding indicates that cells in bronchoalveolar lavage fluids from sarcoid patients were fully capable of acting as antigen-presenting cells. The identification of antigen-presenting cells in the lungs of patients with sarcoidosis together with the previous findings of activated T cells, enhanced IL 1 production, and spontaneous interleukin 2 release in sarcoid patients is compatible with the hypothesis that local cell-mediated immunity is involved in the pathogenesis of pulmonary sarcoidosis.