Protection against Poly Microbial Sepsis by Chitin oligomers is fine tuned by N-Acetyl D-Glucosamine residues

Chitin, poly-N Acetyl D-glucosamine, is an abundant polysaccharide produced by fungal cell walls, insect epicuticle and nematodes cuticles. Its immunomodulatory function has curious attributes - paradoxically opposing host responses using different host receptors resulting in immunostimulatory or immunosuppressive propertis depending on the size/length of the oligomers as well as aceytylation levels have been reported in literature. Here we demonstrate that Hepta-N-Acetyl Chitoheptaose (7 mer) is a TLR2 ligand, 8 mer activates immune cells through TLR4 while, 6 mer is a relatively poor ligand for both TLR2 and TLR4 in generating inflammatory host cytokines. Significantly enhanced inflammatory response characterized by increased TNF-a, IL-1b, IL-6 and IL-10 was a feature of only 8 mer while, 6 and 7 mers induced modest activation in both HEK cells (transfected with specific TLRs) and in human THP2 cells in vitro. The translational significance of these features were addressed in an experimental model of Sepsis using Cecal Ligation Puncture (CLP) protocol, a murine model, considered a gold standard for human Sepsis. More significantly, therapeutic rather than prophylactic administration, that simulates real life scenerio of human and animal sepsis, of 7 mer rather than 6 or 8 residues of Chitin oligomer, significantly protected mice against sepsis as shown by decreased mortality and decreased induction of inflammatory cytokines. These findings suggest that modulation of immune response by chitopolysaccarides in-vivo is precisely caliberated.