Ca++ and 1,25(OH)2D3 enhance peritoneal macrophage (PMPhi) antimicrobial functions in CAPD

Ca++ has been proposed as an intracellular second messenger for the activation of immune cells. An immune regulatory role for 1,25(OH)2D3 has also been suggested. We therefore evaluated the role of Ca++ and 1,25(OH)2D3 in the depressed antibacterial functions of 8 CAPD patients with relapsing bacterial peritonitis by evaluating in vitro the effects of escalating concentrations of 1,25(OH)2D3 and/or Ca++ on: 1. peritoneal macrophage (PMO) cytoplasmic Ca++; 2. PMO superoxide generation; 3. PMO leukotriene B4 release, 4. PMO bacterial killing. Results showed a dose-dependent increase in all parameters for Ca++ concentrations from 500 to 3,000 microM while with both a CA(++)-free medium and with Ca++ concentrations of 5,000 microM of medium all the aforementioned functions were abrogated. Addition of low doses of 1,25(OH)2D3 strongly potentiated the stimulatory effect of Ca++ on cell functions, while high doses were inhibitory. These in vitro data underline the importance of Ca++ and 1,25(OH)2D3 in PMO antibacterial functions in CAPD patients, and may be useful in the prophylaxis and therapy of peritonitis.