Elevation of Granulomatous Lymph-node and Serum Lysozyme in Sarcoidosis and Correlation with Angiotensin-converting Enzyme

Abstract

Granulomatous lymph nodes, lungs, and sera from patients with sarcoidosis were investigated for lysozyme and angiotensin-converting enzyme contents to determine whether the sarcoid granulomas might be the source of elevated serum lysozyme and to explore the relationship between lysozyme and angiotensin-converting enzyme in sarcoidosis. Lysozyme was assayed turbidimetrically with Micrococcus lysodeikticus as substrate. Angiotensinconverting enzyme was assayed spectrophotometrically (tissues) and spectrofluorimetrically (serum) with the substrate hippuryl- L-histidyl-L-leucine. Lysozyme was significantly and markedly elevated in sarcoid lymph nodes (9.05 ± 1.53 µg/mg protein; n = 11) compared with normal controls (1.57 ± 0.40 µg/mg; n = 5; p < .01). Serum lysozyme and angiotensin-converting enzyme were significantly, positively correlated in sarcoidosis patients (r = 0.73; p < .01) and generally tended to vary together in patients studied serially with or without steroid therapy. A significant correlation between lysozyme and angiotensin-converting enzyme was also found in five normal and 11 sarcoid lymph nodes (r = .72; p>.01), but this correlation was not significant for the 11 sarcoid lymph nodes alone (r = 0.424; p > .05). Lysozyme in the lung in sarcoidosis (5.66 ± 1.57 µg/mg protein; n = 5) was similar to control levels (5.73 ± 0.66 µg/mg; n = 4), probably due mainly to normally high lysozyme levels in lung and variable fibrosis in the sarcoid lung. It is suggested that active synthesis of lysozyme by the granulomas may be responsible for elevation of this enzyme in the serum in sarcoidosis, and that the biosynthesis of lysozyme and that of angiotensin-converting enzyme may be controlled at a similar high level.