OBJECTIVE: To make a comparison of serum levels of immunoglobulin G (IgG) subclasses in adult continuous ambulatory peritoneal dialysis (CAPD) patients with those in age- and sex-matched hemodialysis patients and healthy volunteers, and to analyze the contribution of removal of these proteins in peritoneal effluent to their plasma values. DESIGN: A cross-sectional study. SETTING: A renal unit of a university hospital. PATIENTS: Twenty-three CAPD patients, 21 hemodialysis patients, and 21 healthy volunteers. Peritoneal transport studies were done in 8 of the 23 CAPD patients. METHODS: IgG subclasses were measured in serum by nephelometry. For the peritoneal transport studies an ELISA method on ethylenediamine tetracetic acid plasma was used. The same method was used in seven-to-ten-fold concentrated peritoneal dialysate. RESULTS: CAPD patients had lower IgG2 and IgG4 levels than hemodialysis patients and healthy volunteers (p < 0.01). IgG2 values below 1.5 g/L were present in 43% of the CAPD patients (p < 0.001 compared to healthy volunteers). Peritonitis incidence was not different between CAPD patients with low or normal IgG2 plasma levels. Peritoneal clearance of IgG3 was lower than that of the other subclasses. Evidence was obtained for a depressed synthesis of IgG2 and IgG4 in CAPD patients. The hypothesis that interleukin-2 may be involved in the low synthesis rate of IgG2 is discussed. CONCLUSION: Low serum IgG2 and IgG4 levels are present in stable, adult CAPD patients. These were not caused by increased peritoneal loss, but by decreased synthesis.

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