Morphological analysis of the relation between immunoglobulin A production in the small intestine and the enteric nervous system

MZB1 promotes the secretion of J-chain-containing dimeric IgA and is critical for the suppression of gut inflammation

IgA is the most abundantly produced antibody in the body and plays a crucial role in gut homeostasis and mucosal immunity. IgA forms a dimer that covalently associates with the joining (J) chain, which is essential for IgA transport into the mucosa. Here, we demonstrate that the marginal zone B and B-1 cell-specific protein (MZB1) interacts with IgA through the α-heavy-chain tailpiece dependent on the penultimate cysteine residue and prevents the intracellular degradation of α-light-chain complexes. Moreover, MZB1 promotes J-chain binding to IgA and the secretion of dimeric IgA. MZB1-deficient mice are impaired in secreting large amounts of IgA into the gut in response to acute inflammation and develop severe colitis. Oral administration of a monoclonal IgA significantly ameliorated the colitis, accompanied by normalization of the gut microbiota composition. The present study identifies a molecular chaperone that promotes J-chain binding to IgA and reveals an important mechanism that controls the quantity, quality, and function of IgA.

Stress modulates intestinal secretory immunoglobulin A

Stress is a response of the central nervous system to environmental stimuli perceived as a threat to homeostasis. The stress response triggers the generation of neurotransmitters and hormones from the hypothalamus pituitary adrenal axis, sympathetic axis and brain gut axis, and in this way modulates the intestinal immune system. The effects of psychological stress on intestinal immunity have been investigated mostly with the restraint/immobilization rodent model, resulting in an up or down modulation of SIgA levels depending on the intensity and time of exposure to stress. SIgA is a protein complex formed by dimeric (dIgA) or polymeric IgA (pIgA) and the secretory component (SC), a peptide derived from the polymeric immunoglobulin receptor (pIgR). The latter receptor is a transmembrane protein expressed on the basolateral side of gut epithelial cells, where it uptakes dIgA or pIgA released by plasma cells in the lamina propria. As a result, the IgA-pIgR complex is formed and transported by vesicles to the apical side of epithelial cells. pIgR is then cleaved to release SIgA into the luminal secretions of gut. Down modulation of SIgA associated with stress can have negative repercussions on intestinal function and integrity. This can take the form of increased adhesion of pathogenic agents to the intestinal epithelium and/or an altered balance of inflammation leading to greater intestinal permeability. Most studies on the molecular and biochemical mechanisms involved in the stress response have focused on systemic immunity. The present review analyzes the impact of stress (mostly by restraint/immobilization, but also with mention of other models) on the generation of SIgA, pIgR and other humoral and cellular components involved in the intestinal immune response. Insights into these mechanisms could lead to better therapies for protecting against pathogenic agents and avoiding epithelial tissue damage by modulating intestinal inflammation.

Neuronal and nonneuronal cholinergic structures in the mouse gastrointestinal tract and spleen

Accumulating evidence demonstrates that acetylcholine can directly modulate immune function in peripheral tissues including the spleen and gastrointestinal tract. However, the anatomical relationships between the peripheral cholinergic system and immune cells located in these lymphoid tissues remain unclear due to inherent technical difficulties with currently available neuroanatomical methods. In this study, mice with specific expression of the tdTomato fluorescent protein in choline acetyltransferase (ChAT)-expressing cells were used to label preganglionic and postganglionic cholinergic neurons and their projections to lymphoid tissues. Notably, our anatomical observations revealed an abundant innervation in the intestinal lamina propria of the entire gastrointestinal tract principally originating from cholinergic enteric neurons. The aforementioned innervation frequently approached macrophages, plasma cells, and lymphocytes located in the lamina propria and, to a lesser extent, lymphocytes in the interfollicular areas of Peyer's patches. In addition to the above innervation, we observed labeled epithelial cells in the gallbladder and lower intestines, as well as Microfold cells and T-cells within Peyer's patches. In contrast, we found only a sparse innervation in the spleen consisting of neuronal fibers of spinal origin present around arterioles and in lymphocyte-containing areas of the white pulp. Lastly, a small population of ChAT-expressing lymphocytes was identified in the spleen including both T- and B-cells. In summary, this study describes the variety of cholinergic neuronal and nonneuronal cells in a position to modulate gastrointestinal and splenic immunity in the mouse.

Neuronal nitric oxide synthase mediates the effect of ethanol on IgA

AIMS

We showed previously that the acute effect of ethanol on intestinal immunoglobulin A (IgA) expression might be mediated by endogenous nitric oxide (NO). To extend these findings, this study was designed to investigate a possible role of neuronal NO synthase (nNOS) in the observed phenomenon, using 7-nitroindazole (7-NI), a selective inhibitor of its activity.

METHODS

Adult male Wistar rats were treated with: (a) ethanol (4 g/kg, intraperitoneally, i.p.), (b) 7-NI (25 mg/kg, i.p.) followed by ethanol (4 g/kg, i.p.) 30 min later and (c) 7-NI (25 mg/kg, i.p.) followed by saline 30 min later. Untreated rats were used as controls. The concentrations of serum and intestinal IgA were measured by enzyme-linked immunosorbent assay, while the expression of nNOS was determined using western blot and immunohistochemistry.

RESULTS

Acute ethanol treatment significantly increased the concentration of IgA in the ileal extracts, whereas it decreased its serum level. Inhibition of nNOS activity by 7-NI abolished this action of alcohol on IgA. Additionally, western blot analysis revealed that the acute alcohol administration induced an increase in the expression of intestinal nNOS. Furthermore, nNOS-immunoreactive cells, observed within the lamina propria of small intestine, were numerous in ethanol-treated rats.

CONCLUSION

Taken together, these results extended our previous findings suggesting that nNOS mediates the acute effect of ethanol on IgA and supported an immunomodulatory role of this enzyme isoform.

Neural signaling in the spleen controls B-cell responses to blood-borne antigen

Entry of blood-borne pathogens into the spleen elicits a series of changes in cellular architecture that culminates in the systemic release of protective antibodies. Despite an abundance of work that has characterized these processes, the regulatory mechanisms that coordinate cell trafficking and antibody production are still poorly understood. Here, marginal zone (MZ) B cells responding to streptococcus in the blood were observed to migrate along splenic nerves, arriving at the red pulp venous sinuses where they become antibody-secreting cells. Electrical stimulation of the vagus nerve, which in turn regulates the splenic nerve, arrested B-cell migration and decreased antibody secretion. Thus, neural circuits regulate the first wave of antibody production following B-cell exposure to blood-borne antigen.

Effect of Lianshu preparation on lipopolysaccharide-induced diarrhea in rats

AIM: To investigate the effect of Lianshu preparation on lipopolysaccharide (LPS)-induced diarrhea in rats.

METHODS: A diarrhea model was established in Sprague Dawley rats via injection of 1 mL of 30 mg/kg LPS. A total of 40 rats were randomly divided into normal group, LPS group, LPS + Lianshu group, LPS + berberine group (n = 10 in each group). Their intestinal mucosal barrier and frequency of diarrhea were observed. Levels of glucose, serum Na⁺, K⁺, Cl^- and hematocrit, plasma nitrogen monoxide (NO), diamine oxidase (DAO), and D (-)-lactate were measured. The number of IgA+ plasma cells in small intestine was detected and SIgA levels in the intestinal fluid were measured. The antipyretic activity of Lianshu preparation in rats was evaluated using Brewer’s yeast-induced pyrexia (10 mL/kg of 20% aqueous suspension). Acetaminophen (250 mg/kg, intragastric administration, bid) was used as a standard drug for comparison. Temperature was recorded 1 h before and 6 h after Brewer’s yeast injection. Finally, small intestinal transmission in mice treated with Lianshu was detected after intraperitoneal injection of methyl prostigmin (2 mg/kg). Atropine (10 g/kg) was used as a control. The ink content in intestine was determined and the total length of intestine was measured.

RESULTS: The frequency of diarrhea was higher in LPS group than in LPS + Lianshu group and LPS + berberine group (36.70 ± 5.23 vs 28.50 ± 4.06 and 32.70 ± 9.30 respectively, P < 0.01), and lower in LPS + Lianshu group than in LPS + berberine group (P = 0.03). The levels of Na⁺, glucose, Cl^-, K⁺ were significantly lower in LPS + Lianshu group than in LPS + berberine group (140.35 ± 3.19 mmol/L vs 131.99 ± 4.86 mmol/L, 8.49 ± 1.84 mmol/L vs 6.54 ± 2.30 mmol/L, 106.29 ± 4.41 mmol/L vs 102.5 ± 1.39 mmol/L, 5.08 ± 0.66 mmol/L vs 4.32 ± 0.62 mmol/L respectively, P < 0.05). The level of hematocrit was lower in LPS + Lianshu group than in LPS + berberine group (0.50% ± 0.07% vs 0.59% ± 0.10% respectively, P < 0.05). The plasma levels of NO, DAO and D (-)-lactate were higher in LPS group than in normal group (79.74 ± 7.39 &mgr;mol/L vs 24.94 ± 3.38 &mgr;mol/L, 2.48 ± 0.42 &mgr;/mL vs 0.82 ± 0.33 &mgr;/mL, 5.63 ± 0.85 &mgr;g/mL vs 2.01 ± 0.32 &mgr;g/mL respectively, P < 0.01), and lower in LPS + Lianshu group than in LPS + berberine group (48.59 ± 4.70 &mgr;mol/L vs 51.56 ± 8.38 &mgr;mol/L, 1.43 ± 0.53 &mgr;mol/mL vs 1.81 ± 0.42 &mgr;mol/mL, 4.00 ± 0.54 &mgr;g/mL vs 4.88 ± 0.77 &mgr;g/mL respectively, P < 0.05). The morphology of the intestinal mucosa showed destroyed villi in LPS group and atrophied intestinal mucosa in other groups. The pathological intestinal mucosal changes were less in LPS + Lianshu group than in LPS group. The number of IgA+ plasma cells and amount of SIgA were higher in LPS + Lianshu group than in LPS group (1.16 ± 0.19/&mgr;m²vs 1.09 ± 0.28/&mgr;m², P = 0.026; 0.59 ± 0.12 mg/L vs 0.15 ± 0.19 mg/L respectively, P = 0.000). Lianshu had counteractive effects on yeast-induced pyrexia and enterokinesia in rats.

CONCLUSION: Lianshu preparation has therapeutic effects on LPS-induced diarrhea and enterokinesia in rats.

Morphological relationships between peptidergic nerve fibers and immunoglobulin A-producing lymphocytes in the mouse intestine

Immunoglobulin A (IgA) lymphocytes are present close to the nerve fibers in the lamina propria of the small intestine, and the administration of lipopolysaccharides (LPSs) increases the number of these cells and IgA secretion to the lumen. In the present study, we demonstrated that the nerve fibers immunoreactive for vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) were close to the IgA lymphocytes in the mouse ileum lamina propria. Three hours after intraperitoneal administration of LPSs, IgA lymphocytes close to VIP nerve fibers, those close to basement membrane, and those close to both VIP nerve fibers and basement membrane were increased in number. Further, all IgA lymphocytes seen in the ileum lamina propria expressed the receptors for VIP, VIPR1, and VIPR2. Electron microscopy revealed that varicosities were in close apposition to the lymphocyte plasma membrane. The present study suggests that VIP/NPY/CGRP neurons in the submucosal plexus have a close anatomical relationship to IgA lymphocytes, playing a role in the secretion of IgA and intestinal fluid in response to stimulation by lipopolysaccharides, pathogens, or toxins.

Possible mechanism of acute effect of ethanol on intestinal IgA expression in rat

The purpose of this study was to investigate the possible mechanism of acute effect of ethanol on IgA expression in rat intestine. To this end, adult female Wistar rats showing diestrus day 1 were treated with (a) ethanol (2 or 4 g/kg, i.p.); (b) N omega-nitro-L-arginine-methyl ester (L-NAME), which inhibits the activity of all isoforms of nitric oxide synthase, (30 mg/kg, s.c.) followed by ethanol 3 h later; and (c) L-NAME (30 mg/kg, s.c.) followed by saline 3 h later. Saline-injected and untreated rats were used as controls. The animals were sacrificed 0.5 h after ethanol administration. Intestinal expression of IgA was evaluated by both immunohistochemistry and Western immunoblotting. Morphometric analysis showed that acute ethanol treatment increased the number of IgA-immunoreactive cells in a dose-dependent manner. Pretreatment with L-NAME abolished this action of alcohol. Injection of L-NAME followed by saline had no influence on the number of IgA+cells. The results, obtained by Western immunoblotting, paralleled our immunohistochemical findings. Taken together, these data suggest that acute effect of ethanol on intestinal IgA might be mediated by endogenous nitric oxide.