Effect of human intestinal macrophages on immunoglobulin production by human intestinal mononuclear cells isolated from patients with inflammatory bowel disease

Colonic IgA producing cells and macrophages are reduced in recurrent and non-recurrent Clostridium difficile associated diarrhoea

BACKGROUND

In Clostridium difficile associated diarrhoea (CDAD), histological changes in the colonic mucosa range from minimal inflammation to pseudomembranous colitis (PMC). The disease also recurs in a considerable proportion of patients.

AIM

To investigate mucosal immune system cells in colonic biopsies of patients with CDAD.

METHODS

Colonic biopsies were obtained from 12 control patients with diarrhoea, six patients with CDAD and minimal inflammation, and 10 patients with CDAD with pseudomembranous colitis (samples obtained from areas with and without inflammatory exudate). Immunohistochemical studies were performed using antibodies to T cells (CD3), macrophages (CD68), B/plasma cells (CD79alpha), and to IgA, IgM, and IgG. Labelled cells in lamina propria were quantified.

RESULTS

In contrast to T cells, there were significant reductions in B/plasma cell and macrophage counts in all biopsies from patients with CDAD compared with controls (p<0.001). Studies using anti-immunoglobulin antibodies showed significant reductions in IgA producing cells in CDAD biopsies (p<0.05), with the greatest reduction in samples from patients with PMC. In contrast, there was a significant increase (p<0.05) in IgG producing cells in CDAD biopsies. Only patients with PMC relapsed. In these patients, B/plasma cell and IgA producing cell counts (in biopsies with and without inflammatory exudates) were significantly lower (p<0.01) in mucosal samples from those who subsequently relapsed (five) than those who did not.

CONCLUSIONS

A selective reduction in mucosal IgA producing cells and macrophages is associated with colonic disease in C difficile infected patients. Severe reduction in colonic IgA producing cells may predispose to recurrence of CDAD.

Rotavirus-specific intestinal immune response in mice assessed by enzyme-linked immunospot assay and intestinal fragment culture

Primate rotavirus strain RRV and bovine strain WC3 or reassortants made between these animal viruses and human rotaviruses have been administered to infants as candidate vaccines. We compared RRV and WC3 in a murine model of oral infection. We determined the relative capacities of these viruses to induce a virus-specific humoral immune response by intestinal lymphocytes as tested by enzyme-linked immunospot assay, intestinal fragment culture, and enzyme-linked immunosorbent assay of intestinal contents. We found that inoculation of mice with RRV induced higher frequencies of virus-specific immunoglobulin A (IgA)-secreting cells in the lamina propria, greater quantities of virus-specific IgA in intestinal fragment cultures, and greater quantities of virus-specific IgA in intestinal secretions than did inoculation with WC3 or inactivated RRV (iRRV). The induction of an IgA response in serum was predictive of an IgA response among intestinal lymphocytes after inoculation with RRV but not WC3. In addition, large quantities of IgG, IgA, and IgM not specific for rotavirus were produced in fragment cultures from mice inoculated with RRV but not in cultures from mice inoculated with WC3 or iRRV. Possible mechanisms of RRV-induced polyclonal stimulation of intestinal B cells are discussed.

Detection of mRNAs for macrophage products in inflammatory bowel disease by in situ hybridisation

In situ hybridisation has been used to detect mRNAs to the macrophage secretory products, lysozyme, interleukin 1 beta and tumour necrosis factor-alpha. Sections of paraformaldehyde fixed, frozen colonoscopic biopsies from patients with ulcerative colitis, Crohn's disease or normal controls were hybridised with specific radiolabelled probes and the signal detected by autoradiography. Lysozyme mRNA expression was more common in ulcerative colitis (22/27) and Crohn's disease (eight of eight) compared with controls (17/27). Positive cells were found mainly in the subepithelial region in normal colon, while in inflammatory bowel disease they also appeared in the deeper lamina propria. Immunocytochemistry in parallel sections showed that lysozyme mRNA was expressed only in macrophages or in metaplastic Paneth cells in longstanding inflammatory bowel disease. Tissue neutrophils did not express the lysozyme mRNA, though they have large stores of the protein. Tumour necrosis factor mRNA was detected in four of nine controls compared with 11/15 inflammatory bowel disease patients. For interleukin 1 beta, three of eight controls were positive compared with 10/13 with ulcerative colitis. The tumour necrosis factor signal was located mainly in the deeper lamina propria whereas the interleukin 1 beta was seen in subepithelial macrophages. These results confirm increased macrophage activation in inflammatory bowel disease and suggest functional heterogeneity within the intestinal macrophage population.

Tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-6 expression in inflammatory bowel disease

The etiology of ulcerative colitis (UC) and Crohn's disease (CD) remains enigmatic. Infiltrating intestinal macrophages are capable of producing the proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6). We investigated the presence of IL-6, TNF-alpha and IL-1 beta mRNA transcripts in inflammatory bowel disease (IBD), normal, and other inflammatory intestinal specimens utilizing the polymerase chain reaction (PCR). TNF-alpha mRNA levels did not very between inflammatory bowel disease and control specimens. IL-1 beta mRNA levels were highest in active UC and noninflammatory bowel disease inflammatory specimens while IL-6 mRNA levels were highest in active IBD specimens. Infiltrating T cells, macrophages, and B cells were identified as sources of IL-6 protein in inflammatory bowel disease specimens by immunofluorescent staining. IL-6 transcripts were elevated only in active inflammatory bowel disease specimens, suggesting that IL-6-mediated immune processes are ongoing in the inflammatory mucosal environment of CD and UC.

Lymphocyte and macrophage subpopulations in pelvic ileal pouches

This study aimed to characterise the mucosal cellular infiltrate in ileal reservoirs with and without pouchitis (reservoir ileitis). Intraepithelial lymphocyte counts were performed in biopsy specimens obtained from ileal pouches and compared with counts in normal ileum and normal colon. T lymphocyte and macrophage subpopulations were characterised immunohistochemically in pouch biopsy specimens using a panel of monoclonal antibodies. Normal ileum was used as a control. Intraepithelial lymphocyte densities (expressed as intraepithelial lymphocyte/100 epithelial cells) in pouches with and without pouchitis were significantly less than in normal ileum, and approached counts found in normal colon. There was no significant increase in counts even in pouchitis. There were no significant differences in the helper/inducer to suppressor/cytotoxic T cell (CD4:CD8) ratios between normal ileum and pouches with or without pouchitis, either in the epithelium or in the lamina propria. The proportions of RFD9+ (epithelioid cells and tingible body macrophages) and 3G8+ (CD16) macrophages were significantly higher in pouchitis compared with pouches without pouchitis or normal ileum. There were no significant differences between the three groups in the proportions of cells positive for the other macrophage markers (CD68, RFD1-dendritic cells, and RFD7-mature macrophages). The significance of low intraepithelial lymphocyte counts in ileal pouches is unknown, but this may be an adaptive response to the new luminal environment. Since an increase in RFD9+ macrophages occurs in inflammatory bowel disease, but does not occur as a non-specific response to an acute infective process, their presence in pouchitis suggests that effector mechanisms similar to those triggering the original ulcerative colitis may be operating in pouchitis.