Elevation of angiotensin-converting enzyme in granulomatous lymph nodes and serum in sarcoidosis: clinical and possible pathogenic significance

Abstract

A statistically highly significant elevation of serum ACE was found in a group of 58 patients with sarcoidosis (serum ACE was elevated in 34% of patients), as compared with normal controls and patients with tuberculosis and various other common diseases. The results suggest that serum ACE is a useful aid for the diagnosis of sarcoidosis when elevated, but that a normal value does not rule out the condition and may occur in more than one-half of monitored patients. There is a trend to diminution of serum ACE with increasing duration of disease with or without steroid therapy, perhaps correlating with the total body mass of active granulomas, as indirectly suggested in preliminary data by correlation of serum ACE with serum globulin in 16 sarcoidosis patients. It is not yet clear whether there is any significant steroid effect on serum ACE, but a significant number of patients on steroid therapy for more than 2-4 yr have elevated serum ACE values, which in some instances are extremely high. There was a 12-fold elevation in ACE to specific activities generally exceeding those of normal lung in granulomatous lymph nodes of 14 patients with sarcoidosis, suggesting that sarcoid granulomas may be actively synthesizing ACE and resulting in elevation of serum ACE. Extensively fibrotic sarcoid lymph nodes had normal or slightly elevated ACE, suggesting that obliteration of granulomas in sarcoid lymph nodes diminishes their ACE content and that this obliteration may be related to the tendency to diminution of serum ACE with time. ACE was not elevated in one tuberculous lymph node or in experimental granulomas, suggesting that elevation of ACE may have some specificity for the granuloma of sarcoidosis rather than being a characteristic of all granulomas. The catalytic and physical properties of ACE in serum and lymph nodes in sarcoidosis were generally similar to normal ACE with respect to pH activity, modulators, polyacrylamide-gel electrophoresis, and Sephadex G-200 gel filtration. However, sarcoid lymph node ACE appeared to be more heat labile than normal lung or lymph node ACE, suggesting the possibility that an abnormal ACE may be present in sarcoidosis. If an abnormal enzyme is indeed present, it might be coded for by a host gene that is not normally expressed or a nonhost gene or it might be a normal ACE that has been altered. No ACE activity was found in circulating white blood cells in sarcoidosis or in control subjects, suggesting that circulating white blood cells may not contain the epithelioid cell precursor or that ACE synthesis (or less likely, uptake) may be turned on at a later stage in the transformation. Lysozyme activity was also elevated in sarcoid lymph nodes. Serum ACE and serum lysozyme were significantly positively correlated in 16 sarcoidosis patients, suggesting a relationship between the two...