Our objective was to determine the incidence of peritonitis episodes with an impaired initial cell reaction (IICR:neutrophil number < 100 x 10(6)/L) over a period of ten years, and to find possible explanations for this unusual presentation of peritonitis. A retrospective review of the files of continuous ambulatory peritoneal dialysis (CAPD) patients included in the CAPD program 1984 and 1993 was done. Analysis of cytokine and prostanoid patterns during four peritonitis episodes with an IICR was compared to 12 episodes with a normal initial cell reaction (NICR). Dialysate cell numbers and immunoeffector characteristics of peritoneal cells were compared in 7 IICR patients in a stable situation and a control group of 70 stable CAPD patients. The setting was a CAPD unit in the Academic Medical Center in Amsterdam. Thirty-five CAPD patients who had one or more peritonitis episodes with an IICR and a control group of 249 CAPD patients were included in the study. The incidence of peritonitis with an IICR was 6%. These episodes occurred more than once in 51% of the patients who presented with IICR. In 72% the cell reaction was only delayed: a cell number exceeding 100 x 10(6)/L was reached later. Staphylococcus aureus was significantly more frequently the causative microorganism compared to all peritonitis episodes (PE) that occurred during the study period. Patients with IICR had lower dialysate cell counts in a stable situation, compared to a control group (p < 0.01). This was caused by a lower number of macrophages and CD4 positive lymphocytes. The phagocytosis capacity of the macrophages appeared to be normal. In a comparison of four PE with an IICR and 12 episodes with an NICR, the tumor necrosis factor-alpha (TNF-alpha) response was similar and occurred on day 1, also pointing to normally functioning macrophages. However, the maximal appearance rates of interleukin-6 (IL-6) and IL-8 occurred later in the episodes with IICR compared to NICR (day 2 vs day 1, p < 0.05). No differences were found in vasodilating prostaglandins, mesothelial cell markers (cancer antigen 125, phospholipids, hyaluronan), and mesothelial cell numbers in the stable situation nor during peritonitis. Peritonitis can present as abdominal pain in the absence of a cloudy dialysate. In some of the patients this presentation occurred more than once. This impaired, most often delayed, cell reaction was associated with a delayed secondary cytokine response. As IL-6 and IL-8 can be synthesized by mesothelial cells, this suggests an impaired functioning mesothelium. This could not be confirmed, however, by a lower number of mesothelial cells in effluent or lower dialysate levels of mesothelial cell markers.

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