Reduced expression of CD44 on monocytes and neutrophils in systemic lupus erythematosus: relations with apoptotic neutrophils and disease activity

Background-Increased numbers of apoptotic neutrophils, and impaired monocyt e/macrophage clearance of apoptotic cells, have been demonstrated in system ic lupus erythematosus (SLE). CD44 is implicated in the clearance of apopto tic neutrophils. Objective-To determine the expression of CD44 on peripheral blood monocytes and neutrophils in SLE, and examine the relations with disease activity an d numbers of circulating apoptotic neutrophils. Methods-Peripheral blood was sampled from 31 patients with SLE, 19 healthy normal subjects, and 19 patients with rheumatoid arthritis (RA). Monocyte a nd neutrophil density of surface CD44 expression was determined by immunofl uorescence labelling and flow cytometry, and results expressed as mean chan nel fluorescence (MCF) values. Neutrophil apoptosis was measured by morphol ogy in 15 patients with SLE, nine with RA, and six normal subjects. Results-Monocyte CD44 expression was significantly lower in SLE (median MCF 4.71) than in healthy normal subjects (median MCF 5.61) and controls with RA (median MCF 5.39). Neutrophil CD44 expression was also significantly low er in SLE (median MCF 1.95) than in healthy normal subjects (median MCF 2.3 7) and controls with RA (median MCF 2.60). Monocyte, but not neutrophil, CD 44 expression correlated negatively with the percentage of apoptotic neutro phils. There was no significant correlation of monocyte or neutrophil CD44 expression in SLE with disease activity or damage. Conclusions-Monocyte and neutrophil CD44 expression is reduced in SLE, and this may contribute to the impaired recognition and clearance of apoptotic neutrophils by monocyte derived macrophages.