Abstract With its abundance of neurons and immuno- cytes, the gut is a potentially important site for the study of the interaction between the nervous and immune sys- tems. Using immunohistochemical techniques, we tested the hypothesis that gut-associated lymphoid tissue in the porcine small intestine might receive catecholaminergic, cholinergic and peptidergic innervation. Antibodies against protein gene product (PGP) 9.5 were employed to detect neuronal membranes; antibodies against tyro- sine hydroxylase (TH), type 2 vesicular monoamine transporter (VMAT-2) and choline acetyltransferase (ChAT) were used to detect catecholaminergic and cho- linergic neurons; and antibodies to neuromedin U-8 (NMU-8), substance P (SP) and vasoactive intestinal peptide (VIP) were also used. PGP9.5-immunoreactive nerve fibers were observed between jejunal Peyer’s patch (PP) follicles and in submucosal ganglia localized at the base of continuous ileal PP. Many ChAT-positive and a few TH-/VMAT-2-immunoreactive neurons or ax- ons adjacent to jejunal and ileal PP were observed. Neu- rons and fibers from ganglia situated between or at the base of PP follicles manifested robust immunoreactivi- ties to VIP and NMU-8; relatively less SP immunoreac- tivity was observed at these locations. All neuromedin-U 8-positive neurons observed exhibited immunoreactivity to ChAT as did some VIP-positive neurons. The specific chemical coding of enteric neurons in close apposition to jejunal and ileal PP and the differential localization of neuropeptides within the jejunal and ileal PP are indica- tive of neuroimmunomodulation at these sites. Key words Neuroimmunology · Tyrosine hydroxylase · Type 2 vesicular monoamine transporter · Choline acetyltransferase · Neuromedin U-8 · Vasoactive intestinal peptide · Substance P · Peyer’s patch · Pig Introduction Because it comprises a vast surface area in contact with the external environment, the intestinal mucosa contains the largest amount of lymphoid tissue in the body, which functions in host defense against luminal pathogens. The gut-associated lymphoid tissue (GALT) consists of orga- nized regions of lymphoid tissue, such as the Peyer’s patches (PP) and diffuse populations of lymphocytes found in the lamina propria and epithelium of the wall of the gastrointestinal tract (Bienenstock and Befus 1985; Doe 1989; Mowat and Viney 1997). The PP of the small intestine can initiate local and systemic immune respons- es, as well as oral tolerance (Pabst 1987). In porcine small intestine, two types of PP occur: jejunal PP are or- ganized, solitary follicles, whereas ileal PP are continu- ous lymphoid follicles (Binns and Licence 1985). In the jejunum, PP contain a germinal center overlain with a distinctive dome epithelium containing cuboidal micro- fold (M) cells. High numbers of T lymphocytes reside in the interfollicular areas of jejunal PP. The M cells endo- cytose luminal antigens and transport them to antigen- presenting cells and regulatory T cells lying beneath the PP dome to initiate mucosal immune responses (Stokes et al. 1994). In contrast, porcine ileal PP are covered by a villous epithelium devoid of M cells. PP in these two dif- ferent locations also differ in lymphocyte trafficking and B-cell production. For example, lymphocyte homing to jejunal PP is greater than to ileal PP (Binns and Licence 1985). Moreover, jejunal PP possess comparatively more T cells and less B cells than ileal PP (Rothkötter and Pabst 1989). These differences may indicate that jejunal and ileal PP are subject to different regulatory influences. The enteric nervous system (ENS) plays an important role in modulating and coordinating complex intestinal This investigation was supported by NIH grant DA-10200. A.K.-N. is a postdoctoral trainee supported by NIH Psychoneuroimmunol- ogy Training Grant DA-07239. A. Kulkarni-Narla · A.J. Beitz · D.R. Brown ( ✉ ) Psychoneuroimmunology Training Program, Department of Veterinary PathoBiology, University of Minnesota Academic Health Center, 1988 Fitch Avenue, St. Paul, MN 55108-6010, USA e-mail: brown013@tc.umn.edu Tel: +1 612 624 0713 Fax: +1 612 625 0204 Cell Tissue Res (1999) 298:275–286 © Springer-Verlag 1999 Digital Object Identifier (DOI) 10.1007/s004419900096 REGULAR ARTICLE Anjali Kulkarni-Narla · Alvin J. Beitz David R. Brown Catecholaminergic, cholinergic and peptidergic innervation of gut-associated lymphoid tissue in porcine jejunum and ileum Received: 15 January 1999 / Accepted: 15 July 1999 / Published online: 9 September 1999