Soluble CD23 protein in the peritoneal fluid of patients with endometriosis

Activated B cells are known to produce soluble CD23 protein (sCD23) from their membranes. We recently showed a higher concentration of sCD23 in the serum of patients with endometriosis. As the commonest site of endometriosis is the peritoneal cavity, we sought to evaluate the concentration of sCD23 in the peritoneal fluid of 47 fertile symptomatic women with endometriosis and 35 fertile women without endometriosis. Endometriosis was diagnosed by laparoscopy and confirmed by histopathology. There was a statistically significant difference between the sCD23 concentrations in the endometriosis and control groups (P < 0.05). When endometriosis was defined based on the revised American Fertility Society (AFS) Score, patients with mild (AFS 1 and II) but not severe (AFS III and IV) endometriosis showed a higher and significant difference in the concentration of sCD23 when compared with the controls (P < 0.05). There was no significant correlation between the peritoneal fluid concentration of sCD23 and the phase of the menstrual cycle. We conclude that the concentration of sCD23 is higher in the peritoneal fluid of patients with endometriosis when compared with the controls, suggestive of B cell activation in patients with endometriosis. Furthermore, mild endometriosis is immunologically more active than severe endometriosis as defined by the current classification.