Immunomodulatory effects of TLR ligands and polysaccharide combinations : strategies to augment innate immune response

Abstract

Microbial infection initiates multiple TLR ligand mediated signaling cascade on innate immune cells. While some TLRs trigger a Th1 biased immune activation, others may lead to a Th2 dominant immune response. Extracellular (TLR1, 2, 4, 5, 6, 10, and 11) vs endosome-associated TLRs (TLR3, 7/8, and 9) display differential immune activation and cytokine milieu. Understanding contrasting and synergistic behaviors of these TLR subclasses when mixed together may lead to more potent formulations for immunotherapy. Delivery and retaining the stability of nucleic acid based labile TLR ligands to the site of immunologically relevant cells is also a challenge. In the first part of the thesis, optimum TLR combinations with differential immune effects will be brought into light. Next, immunomodulatory effect of a natural polysaccharide (PS) will be characterized. Finally the ability of a PS carrier to form complex with ligands of nucleic acid sensing TLRs and its potential as a controlled delivery vehicle to stimulate the immune cells will be documented. In brief, our results suggest that different PS types extracted from various mushroom sources are immunostimulatory and are targeted to TLR2/6 for delivery of other relevant stimulants. Moreover, certain TLR ligand combinations can be harnessed to induce more robust immune activation compared to their stand alone counterparts. This knowledge will pave the way for establishing an effective PS based carrier of DNA/RNA ligands thus, more effective immunotherapeutic strategies for treating infectious and other local or systemic diseases be possible.