These findings show that secreted antimicrobial peptides are retained by the surface-overlaying mucus and thereby provide a combined physical and antibacterial barrier to prevent bacterial attachment and invasion. This distribution facilitates high local peptide concentration on vulnerable mucosal surfaces, while still allowing the presence of an enteric microbiota.

Administration of dextran sulfate to mice, given in the drinking water results in acute or subacute colonic inflammation, depending on the administration protocol. This colonic inflammation exhibits ulceration, healing and repair, and a therapeutic response that makes it valuable for the study of mechanisms that could act in the pathogenesis of human ulcerative colitis, a disease thought to have an immunologically dependent pathogenesis. To investigate if immunological mechanisms were involved in the induction of colonic inflammation in this model, mice with different degrees of immunodeficiency were used. It was shown that dextran sulfate induced colitis could be induced in Balb/c mice depleted of CD4(+) helper T cells by treatment with monoclonal antibodies preceded by adult thymectomy. The depletion of CD4(+) was verified by flow cytometric analysis. Furthermore, the colonic inflammation could equally be induced in athymic CD-1 nu/nu mice lacking thymus-derived T cells, in T and B-cell deficient SCID mice, and also in SCID mice depleted of NK cells by treatment with anti-asialo GM1 antibodies. The NK-cell depletion was verified by measuring spleen NK-cell activity. The resulting colonic inflammation in all these types of deficient mice was qualitatively comparable, as shown by clinical and histological appearance. These results indicate that the presence of functional T, B and NK cells is not crucial for the induction of dextran sulfate colitis in mice.

The use of germ-free mice offers the possibility to study antibacterial components in a gut uncolonized by bacteria. We have developed a method to extract and high pressure liquid chromatography-fractionate the antibacterial factors present in the small intestine of a single mouse. By mass spectrometry and sequence analyses of fractions exhibiting antimicrobial activity, we identified and characterized the defensin region in germ-free mice as well as in colonized mice. Defensins made up around 15% of the total antibacterial activity both in germ-free and colonized mice. The intestine of germ-free mice exhibited the same set of mature enteric defensins (defensins 1, 2, 3, 4, and 6) as mice colonized by a normal microflora. Mature defensins are generated through processing of larger precursors by enzymatic removal of a signal peptide and a propiece. We found that all prodefensins were cleaved at a Ser/Ala-Leu bond, giving 34-residue propiece peptides and only trace amounts of the predicted 39-residue peptide. This first step must be followed by the removal of a residual peptide to render the mature defensins, indicating that the processing is more complex than previously anticipated. The same propieces were found in both germ-free and colonized mice, suggesting that the same processing operates independent of bacterial presence in the intestine.

Background: Animal models of inflammatory bowel disease are artificial and more or less representative of human disease. However, the dextran sulphate sodium (DSS) induced intestinal inflammation model has recently been shown to fulfil some pathological criteria for an adequate experimental model. Aim: To determine whether this form of experimental intestinal inflammation responds to established therapy used for human inflammatory bowel disease. Methods: DSS was used to induce intestinal inflammation in conventional Balb/c mice and athymic nu/nu CD‐1(BR) mice, and the well‐documented 5‐aminosalicylic acid (5‐ASA) based anticolitis drugs sulphasalazine (SASP) and olsalazine (OLZ) were used to study therapeutic effects. Parameters which have been shown to reflect DSS‐induced intestinal inflammation (body weight, colon length, spleen weight, diarrhoea, and rectal bleeding) were measured in the Balb/c mice. Results: Significant amelioration was seen on these parameters after different treatment protocols. Survival in nu/nu CD‐1 mice was studied, and after 16 days a death rate of 50% was noted in the DSS group. SASP (100 mg/kg/day) and OLZ (50 mg/kg/day) significantly prolonged the survival to 29 and 38 days, respectively. SASP and OLZ showed a dose‐dependent effect in the range between 10 and 100 mg/kg/day, doses closely corresponding to those used in humans. Conclusions: SASP and OLZ are able to ameliorate the DSS‐induced intestinal inflammation. The dose‐response patterns suggested that the active therapeutic moiety for the two drugs appears to be mainly the liberated 5‐ASA molecule.

It has been shown that Bacteroides thetaiotaomicron, a representative member of the gut microflora, signals intestinal epithelial cells both in vivo and in vitro and modulate specific glycosylation processes that may mediate intestinal functions. However it is not known whether these modulations depend on the presence of live bacteria or may be elicited by soluble factors produced in vitro by this bacterium. We used lectins and an histochemical approach to survey tissue sections prepared from various cellular compartments of the small and large intestine of NRMI/KI mice grown under gnotobiotic conditions. We compared the results obtained with bacterial culture supernatant and live B. thetaiotaomicron to those obtained from germ-free mice or mice having a conventional microflora. This approach allowed us to conclude that (1) a small but specific number of glycan patterns were restored after treatment with bacterial culture supernatant and (2) the B. thetaiotaomicron associated mice restored a larger number of patterns, however, the complete conventional mice pattern must be a function of the whole microflora in the gut. The possibility to modulate this complex glycosylation pattern by introducing exogenous bacteria and bacterial products should be considered as a promising approach towards understanding the molecular basis of microbial-host interactions.