Bombesin Improves Adaptive Immunity of the Salivary Gland During Parenteral Nutrition

Abstract

Background: The parotid and submandibular salivary glands are gut-associated lymphoid tissues (GALTs) that secrete immune compounds into the oral cavity. Parenteral nutrition (PN) without enteral stimulation decreases GALT function, including intestinal lymphocyte counts and secretory immunoglobulin A (sIgA) levels. Since the neuropeptide bombesin (BBS), a gastrin-releasing peptide analogue, stimulates intestinal function and restores GALT parameters, we hypothesized that PN + BBS would stimulate parotid and salivary gland IgA levels, T lymphocytes, and IgA plasma cell counts compared with PN alone. Methods: Male (Institute of Cancer Research) ICR mice received intravenous catheters and were randomized to chow with saline, PN, or PN + BBS (15 µg/tid/mouse) for 5 days (8/group), 2 days after cannulation. Salivary glands were weighed and either frozen for IgA and amylase analysis or fixed for histological analysis of acinar cells, IgA+ plasma cells, and T lymphocytes. Small intestinal wash fluid was collected for IgA regression analysis with salivary glands. Results: PN reduced organ weight, acinar cell size, and amylase activity compared with chow; BBS had no significant effects on these parameters. Compared with chow, PN significantly reduced salivary gland IgA levels, IgA+ plasma cells, and T lymphocytes. PN + BBS significantly elevated IgA and restored cellularity compared with PN. Salivary gland tissue homogenate IgA levels significantly correlated with intestinal fluid IgA levels. Conclusions: Compared with chow, PN results in atrophy of the salivary glands characterized by reduced amylase, IgA, and immune cellularity. BBS has no effect on acinar cells or amylase activity compared with PN but maintains tissue IgA and plasma cells and T-lymphocyte numbers compared with chow.