Serum beta-2-microglobulin and angiotensin-converting enzyme activity in sarcoidosis.

Angiotensin-converting enzyme activity in sarcoidosis is regarded both as a diagnostic feature and as an index of disease activity. Increased activity of this enzyme is thought to parallel macrophage and epithelioid cell activity. Beta-2-microglobulin, a low-molecular-weight protein associated with the histocompatibility antigens, is thought to reflect activation of immunocompetent cells, particularly lymphocytes. In 132 patients with known sarcoidosis no close association was found to exist between the results of the two assays (r = 0.53). Angiotensin-converting enzyme activity was raised in 33% and beta 2-microglobulin concentrations in 63% of patients with sarcoidosis. When analysed prospectively, the results of the two assays showed no correlation in 29 patients over periods of up to 19 months. Stage, duration of disease, and corticosteroid treatment showed no significant effect on levels of either angiotensin-converting enzyme or beta 2-microglobulin. The disparity between indices of macrophage and lymphocyte activation requires further study in sarcoidosis.