Immunohistological study in sarcoidosis: evaluation at different sites of disease activity

Sarcoidosis is a multisystem disease characterized by enhanced immune responses at sites of involvement. For this reason, an immunohistological study using monoclonal antibodies against T-cell subpopulations was carried out in order to evaluate the topographic distribution of immunocompetent cells in tissue sections obtained from a variety of involved organs, such as parenchymal lung, lymph nodes, eyes, skin, and liver. Biopsy specimens were also stained for detection of immunoglobulins, complement, and fibrinogen deposits. The data demonstrate a redistribution of T cells from the blood to all the sites of disease activity where they account for the large majority of infiltrating cells, both in the early lesions (merely a lymphocytic infiltrate) and in well-organized granulomas. Moreover, these cells express a helper-related phenotype, as demonstrated by the high Leu-3/Leu-2 ratios, at sites of involvement with respect to the blood (blood, 1.8/1; transbronchial lung biopsies, 10.5/1; lymph nodes, 19/1; skin, 28/1; liver, 22/1; eye, 14/1). In line with this helper infiltration is the presence of plasma cells and immunoglobulin deposits, suggesting a local hyperreactivity of the B-cell immune system. Both the hypergammaglobulinemia and the T lymphopenia usually observed in the blood of sarcoid patients could be explained by these observations. Comparative analysis of immunohistological data and bronchoalveolar lavage (BAL) findings provides further evidence that BAL cellularity reflects the changes already occurring in lung histology. The studies emphasize the importance that immunological phenomena play in the pathogenesis of sarcoidosis and provide new insights into the mechanisms leading to the formation and maintenance of the sarcoid granuloma.