The neuropeptide bombesin improves IgA-mediated mucosal immunity with preservation of gut interleukin-4 in total parenteral nutrition-fed mice

Background. The Th2 cytokines, interleukin-4 (IL-4) and interleukin-10 (IL-10), stimulate IgA production. Total parenteral nutrition (TPN) reduces IL-4 and IL-10 messenger RNA in gut lamina propria lymphocytes, total IL-4 and IL-10 in gut homogenatres, and Ig-A-mediated mucosal immunity. Bombesin (BBS) can maintain mucosal immunity in TPN-fed mice, but the effects of BBS on gut IL-4 and IL-10 levels and their mRNA expression in the lamina propria are unknown. Methods. In experiment 1, mice that were feed chow, TPN, or TPN + BBS (15 mug/kg intravenously-three times a day) for 5 days were killed, and respiratory tract IgA and intestinal IgA, IL-4, and IL-10 levels were measured. In experiment 2, IL-4 and IL-10 mRNA were measure in isolated lamina propria lymphocytes from chow-, TPN-, and TPN+BBS-fed mice by reverse transcriptase-polymerase chain reaction. Intestines were harvested 1 hour after injection of 100 mug of lipopolysaccharide intraperitoneally. Samples were standardized to beta-actin. Results. TPN-fed mice had significantly lower respiratory IgA levels than chow- or TPN+BBS-fed mice. TPN+BBS did not increase intestinal IL-10 or IL-10 lamina propria mRNA levels but maintained intestinal IL-4 levels and lamina propria IL-4 mRNA expression equal to those of chow-fed mice. Conclusions. BBS reverses the effects of TPN on intestinal and respiratory tract IgA levels and most effects on gut cytokines. Lamina propria cytokine mRNA levels reflect total gut cytokine concentration.