Anatomical variation in mast cell nerve associations in the rat small intestine, heart, lung, and skin. Similarities of distances between neural processes and mast cells, eosinophils, or plasma cells in the jejunal lamina propria.

Several studies have indicated that mast cells occur in close proximity to enteric nerves in the gastrointestinal tract of rats, man, and other mammalian species, and such intimate associations have been proposed as one of the anatomical bases of communication between the immune and the nervous systems. However, the specificity of anatomical associations between enteric nerves and mast cells, as opposed to other bone marrow-derived or lymphoid cells normally present in mucosal sites, is unclear. We used transmission electron microscopy to quantify the distances between mast cells and neural processes (nerve terminals or axons) in the small intestinal mucosa, right atrium, skin, and pulmonary parenchyma of normal rats, and in the small intestinal mucosa and lung parenchyma of rats that had undergone hyperplasia of the mast cell populations in these sites as a result of infection with the nematode Nippostrongylus brasiliensis. In the jejunal mucosa of normal rats, 8.0% of mast cells occurred within 100 nm of neural processes and an additional 11.0% between 101 and 500 nm of these structures; the corresponding figures for eosinophils were 3.3% (N.S. vs. mast cell value) and 23.3% (p less than 0.05 vs. mast cell value) and for plasma cells were 8.5% and 14.6% (N.S. vs. mast cell values). In the right atrium, 1.2% of mast cells occurred within 100 nm and an additional 13.4% within 101 and 500 nm of neural processes, whereas no mast cells were observed within 500 nm of neural processes in the pulmonary parenchyma or ear skin. Infection with N. brasiliensis increased by 61% the proportion of mast cells within 500 nm of neural processes in the jejunal mucosa and resulted in the appearance of mast cells in close association with these structures in the jejunal muscularis propria, but had no effect on the proportion of mast cells within 100 or 500 nm of neural processes in the pulmonary parenchyma. Acetylcholine esterase staining demonstrated dense networks of neural processes in the three sites where some mast cells were closely associated with these structures (jejunal mucosa and muscularis, right atrium) but not in the pulmonary parenchyma or ear skin. Taken together, our findings indicate that mast cells occur in close proximity to neural processes in sites where these structures are abundant, but that anatomical associations as close as those between mast cells and neural processes can also occur between such structures and other bone marrow-derived cells (eosinophils) or lymphoid cells (plasma cells) resident in the small intestinal mucosa.(ABSTRACT TRUNCATED AT 400 WORDS)