Chitosan is a cationic polysaccharide derived from the partial deacetylation of chitin, which exhibits particular properties: interacts with negatively charged sites on the cell surface; changes the permeability of intestinal epithelium, enhancing the uptake of peptides and proteins; and activates leukocytes. Antigens coadministered or encapsulated with the polysaccharide show improved mucosal and systemic humoral immune responses, although the mechanism is poorly understood. Herein, we characterized in Peyer's patches mesenteric lymph nodes and spleen molecular events triggered after oral administration of chitosan in the absence of protein antigen. Sixteen hours after feeding, we studied the uptake and distribution of the polysaccharide, the phenotype of recruited antigen-presenting cells (APC), the induction of cytokines such as tumor necrosis factor alpha, interleukin (IL)-12, IL-4, IL-10, and transforming growth factor-beta (TGF-beta), and the activation of T lymphocytes. We show here that the uptake of chitosan at inductive mucosal sites involves CD11b/c+ APC and that chitosan feeding increases the percentage of OX62+ dendritic cells, which up-regulate the major histocompatibility complex class II antigens without changing the expression of costimulatory CD80 or CD86 molecules. The polysaccharide elicits the release of IL-10 as well as the expression of IL-4 and TGF-beta in mucosa, and in spleen, the activation of CD3+ T cells occurs. Our results demonstrate that chitosan acts by enhancing the T helper cell type 2 (Th2)/Th3 microenvironment in the mucosa. A single dose of this polysaccharide exhibits local and systemic effects, and its activity could be relevant in the maintenance of the intestinal homeostasis.

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Oral administration of an antigen can result in local and systemic priming or tolerance and the basis of this dichotomy is poorly understood. The intestinal microenvironment, and factors such as nature of the antigen, dose, genetic background, uptake and concentration of the antigen that gain access to the internal milieu via the mucosa influence these active immunologic processes. Chitosan is a biocompatible natural polysaccharide able to promote the transmucosal absorption of peptides and proteins. The aim of our work was to study the effect of the co-administration of type II collagen (CII) and chitosan during the initial contact of the antigen with the immune system. Sixteen hours after feeding we evaluated several molecular events in mucosal and in systemic lymphoid tissues. We determined in Peyer's patches (PP) and spleen cells the number and activation of T cells, the arrival of the antigens, and the cytokine profile. In PP we found a reduction in the cell number without changes in CD3(+) cells. In spleen, instead, we observed an increase in CD3(+) cells as well as the internalization of the CD3 complex. CII:chitosan-fed animals exhibited a reduced secretion of IL-2 with an increase of IL-10 in PP and spleen respectively. In addition, in PP, CII:chitosan-fed rats showed increased levels of mRNA for transforming growth factor-beta, IL-4 and IL-10. Together, our data suggest that the co-administration with chitosan modifies the uptake and/or the distribution of the relevant antigen, and promotes an anti-inflammatory environment early after feeding.

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Bovine mastitis affects the health of dairy cows and the profitability of herds worldwide. Coagulase-negative staphylococci (CNS) are the most frequently isolated pathogens in bovine intramammary infection. Based on the wide range of antimicrobial, mucoadhesive and immunostimulant properties demonstrated by chitosan, we have evaluated therapy efficiency of chitosan incorporation to cloxacillin antibiotic as well as its effect against different bacterial lifestyles of seven CNS isolates from chronic intramammary infections. The therapeutic effects of combinations were evaluated on planktonic cultures, bacterial biofilms and intracellular growth in mammary epithelial cells. We found that biofilms and intracellular growth forms offered a strong protection against antibiotic therapy. On the other hand, we found that chitosan addition to cloxacillin efficiently reduced the antibiotic concentration necessary for bacterial killing in different lifestyle. Remarkably, the combined treatment was not only able to inhibit bacterial biofilm establishment and increase preformed biofilm eradication, but it also reduced intracellular bacterial viability while it increased IL-6 secretion by infected epithelial cells. These findings provide a new approach to prophylactic drying therapy that could help to improve conventional antimicrobial treatment against different forms of bacterial growth in an efficient, safer and greener manner reducing multiresistant bacteria generation and spread.

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