Effect of a soluble bacterial carbohydrate fraction on the viscosity of intestinal contents in healthy subjects and patients with Crohn's disease

IgM antibody level against proinflammatory bacterial peptidoglycan is inversely correlated with extent of atherosclerotic disease

OBJECTIVE

Atherosclerosis may lead to acute clinical events by rupture of a vulnerable atherosclerotic plaque. Previously, we demonstrated that peptidoglycan (PGN), a major cell wall component of gram-positive bacteria that induces production of proinflammatory cytokines through TLR2 and CD14, is prevalent in atherosclerotic lesions with histological features associated with plaque vulnerability. We hypothesized that in atherosclerotic patients antibody levels against PGN may differ compared with matched controls.

METHODS AND RESULTS

ELISA was performed to measure immunoglobulin levels against PGN in sera of 80 atherosclerotic patients versus 77 control patients with an increased cardiovascular risk, frequency-matched for age, sex and risk factors for atherosclerotic disease. In all patients and controls, intima-media (IMT) thickness was assessed using an array transducer. Significantly lower levels of IgM directed against PGN were found in atherosclerotic patients compared with the control patients without clinically manifested disease (P = 0.02). The IgM levels against PGN decreased with increasing mean common carotid IMT thickness (P = 0.006).

CONCLUSIONS

These results show that patients suffering from atherosclerotic disease have decreased IgM levels against PGN. The data suggest that an antibody response against PGN could have a protective effect against the development or activity of atherosclerotic disease.

Reduced systemic IgG levels against peptidoglycan in rheumatoid arthritis (RA) patients

The gut flora is believed to play a role in the pathogenesis of RA. Peptidoglycan, a major cell wall component of Gram-positive bacteria, is a candidate antigen because of its capability to trigger production of proinflammatory cytokines, to induce arthritis in rodents, and because of its presence in antigen-presenting cells in RA joints. We investigated whether the systemic and local antibody levels against a peptidoglycan-polysaccharide (PG-PS) are related to the presence and disease activity of RA. Significantly lower levels of systemic IgG directed against PG-PS were found in healthy females compared with healthy males, and systemic IgA levels specific for PG-PS were negatively correlated with age. Levels of systemic IgG directed against PG-PS were significantly reduced in RA patients compared with sex- and age-matched healthy controls. Local (synovial fluid) levels of IgG did not correlate with disease activity whereas synovial fluid levels of IgA correlated positively with disease activity. These data suggest that IgG in healthy people mediates protection against spreading of PG to non-mucosal sites.

Background immunoglobulin-secreting cells specific for intestinal peptidoglycan-polysaccharides in mice

Natural antibodies to soluble peptidoglycan-polysaccharide complexes (PPC) from the human intestinal flora have been found in mammalian sera. In this study the occurrence and frequency of PPC-specific immunoglobulin-secreting cells (anti-PPC Ig-SC) were determined in lymphoid organs of normal (C57BL x CBA)F1 mice. One out of 100 IgM-SC in the spleen and Peyer's patches was found to be specific for PPC. In the small intestine a small number of anti-PPC IgA-SC were present probably responsible for IgA secretion in the gut lumen since very low serum concentrations anti-PPC IgA were found. Anti-PPC IgG-SC were not detected, although some anti-PPC IgG was found in the serum. It is concluded that the spleen is the major lymphoid organ responsible for the production of natural antibodies to PPC.

Responses of synovial fluid and peripheral blood mononuclear cells to bacterial antigens and autologous antigen presenting cells

The specificity of T cells in the inflamed joints of patients with rheumatoid arthritis (RA) has been the subject of much study. Bacterial antigens are suspect in the aetiology of rheumatic diseases. The responsiveness of the mononuclear cell fraction of peripheral blood and synovial fluid of patients with RA and of patients with rheumatic diseases other than RA to bacterial antigens such as cell wall fragments of the anaerobic intestinal flora, cell wall fragments of Streptococcus pyogenes, intestinal flora derived peptidoglycan polysaccharide complexes, the 65 kilodalton protein of Mycobacterium tuberculosis, and muramyldipeptide was investigated. No significant difference in response was found to all these bacterial antigens in the synovial fluid of patients with RA compared with the responses in patients with other rheumatic diseases. The highest responsiveness in the synovial fluid of the patients with RA was to the streptococcal cell wall fragments and to the 65 kilodalton protein. Higher responses to several bacterial antigens in the synovial fluid of patients with RA were found compared with peripheral blood from the same patient group. The antigen presenting cell population of the synovial fluid in patients with RA and the patients with other rheumatic diseases was found to be stimulatory for autologous peripheral blood T cells even in the absence of antigen. This suggests an important role for the synovial antigen presenting cell in the aetiology of inflammatory joint diseases.

Are intestinal bacteria involved in the etiology of rheumatoid arthritis? Review article

Observations in bowel-related joint diseases give support to this hypothesis. In Crohn's disease and ulcerative colitis, the bowel wall inflammation is complicated in about 20% of the patients by joint inflammation. Bowel infection by Salmonella, Shigella and Yersinia can provoke joint inflammation and supports an etiological link between bowel bacteria and arthritis. The arthropathic properties of the most abundant group of intestinal bacteria, i.e. the obligate anaerobic bacteria, were studied in an animal model. Cell wall fragments (CWF), with peptidoglycan as the major component, from some Eubacterium and Bifidobacterium species induced a severe chronic polyarthritis in Lewis rats after a single intraperitoneal injection. Eubacterium was found in numbers of 10(8)-10(9) per gram in stools of healthy subjects and rheumatoid arthritis (RA) patients. CWF of isolated strains of E. aerofaciens were arthropathic. Soluble peptidoglycan polysaccharide complexes (PG-PS) originating from the obligate anaerobic flora were purified from human intestinal contents. PG-PS from ileostomy fluid that proved to be less processed by intestinal enzymes induced chronic arthritis in rats after a single administration in oil in the base of the tail. It was concluded that the human intestinal bowel contains soluble bacterial cell wall products that are arthropathic in an animal model. Peptidoglycan (PG) or its subunits was reported to be present in mammalian tissues. Immunohistochemical studies from our group showed the presence of intestinal PG-PS in sections of normal rat spleen. Bacterial cell wall or PG-induced joint inflammation in rats is proven to be absolutely dependent on functional T cells. T-cell lines were isolated from the lymph nodes of rats with an E. aerofaciens CWF arthritis. A helper T-cell line B13 was in vivo arthritogenic in knee or ankle joints upon intravenous injection in rats and proliferated in vitro on syngeneic spleen cells alone, but was additionally stimulated by intestinal PG-PS and E. aerofaciens CWF. It was postulated that the arthritogenic T cells that seem to be autoreactive are, in fact, recognizing bacterial PG-PS on antigen-presenting cells (APC). It is generally accepted that RA is a T-cell-dependent process and that therefore the reaction is directed at small peptides bound by the major histocompatibility complex of APC. The only peptides present in arthritis inducing intestinal PG-PS and in CWF are PG peptides interlinking the sugar chains. We feel that the immunoreaction against PG peptides plays a pivotal role in experimental and human arthritis of an unknown etiology.

Induction of arthritis in rats by soluble peptidoglycan-polysaccharide complexes produced by human intestinal flora

Peptidoglycan-polysaccharide complexes were isolated from feces of a healthy subject and from ileostomy fluid from 5 patients. Peptidoglycan-polysaccharide complexes were tested for arthritogenicity in a rat model, by subcutaneous injection in Freund's incomplete adjuvant. Complexes from the healthy subject did not induce arthritis, but those from ileostomy fluid of 1 of the patients induced severe, chronic joint inflammation. We concluded that peptidoglycan-polysaccharide complexes from intestinal flora are potentially arthritogenic in rats. This arthritogenicity may be influenced by the content of muramic acid and rhamnose in these complexes.

Serum immunoglobulin levels and naturally occurring antibodies against carbohydrate antigens in germ-free BALB/c mice fed chemically defined ultrafiltered diet

This study investigates the influence of exogenous antigenic stimulation on the serum immunoglobulin levels and the levels of circulating natural antibodies against carbohydrate antigens. Thus, BALB/c mice, raised in a germ-free environment and fed a chemically defined, ultrafiltered diet (GF-CD), were employed. These mice had normal serum IgM levels, but IgG and IgA levels were approximately 5% of conventionally reared littermates. The concentrations of all four IgG isotypes were equally low. The variable part of the heavy chains of naturally occurring BALB/c antibodies against a number of carbohydrate antigens, including 3-fucosyllactosamine (3-FL), levan and dextran, are encoded by VH441, and these antibodies express cross-reactive idiotopes recognized by the monoclonal antibodies 6C4 and 6B1. Antibodies against levan and dextran were lower in GF-CD than in conventional mice, but levels of anti-3FL antibodies, and 6C4 and 6B1 idiotopes, were comparable to those in conventional animals. Peptidoglycan polysaccharide complexes (PPC) are carbohydrate antigens of bacterial origin, like levan and galactan. Naturally occurring antibodies against PPC were found in the serum of conventional mice, but were severely reduced in GF-CD mice. The results indicate that most naturally occurring antibodies against carbohydrate antigens of bacterial origin found in conventional mice are caused by exogenous stimulation.