Ultrastructural localization of anionic sites and lectin-binding sites in sarcoid human alveolar macrophages during interaction with T-lymphocytes

Sarcoidosis alveolitis is caused by an unknown stimulus activating alveolar macrophages (AM) and T-lymphocytes. During antigen presentation, the compl ex HLA class II molecule/processed peptide, on the surface of sarcoid AM, i nduces the T-lymphocyte to proliferate. Altered glycosylation patterns of c ell surface glycoproteins such as class II molecules in inflammatory states , may enhance the antigen-presenting capability of AM. In order to know if anionic sites and lectin-binding sites take part in the process of antigen presentation by alveolar macrophages, cells obtained from bronchoalveolar l avage of patients with pulmonary sarcoidosis were incubated with cationized ferritin (CF) and colloidal gold complexed lectins (BSL-I-A(4); RCA-I; RCA -II; WGA) for 30 min at 4 degrees C. After incubation, the cells were fixed with 4% paraformaldehyde, 2% glutaraldehyde, postfixed, and Epon embedded. The CF particles were uniformly distributed over the entire cell surface o f the lymphocyte, and formed clusters on the surface of the macrophage main ly at the adhesion region between the AM and the lymphocytes. We found enha nced binding of BSL-I-A(4) by AM, while WGA and RCA were poorly taken up by these cells. Gold-BSL-I-A(4) was distributed randomly on the plasma membra ne of the AM, and clustered in the adhesion region with lymphocytes. These results suggest that anionic sites and alpha-D-N-acetyl-galactosamine resid ues labeled with gold-BSL-I-A(4) may be involved in the process of antigen presentation by sarcoid alveolar macrophages.