Figure 1. LTR signaling in host defenses against pathogens. Conserved components unique to microorganisms, like bacterial lipopolysaccharide (LPS), bacterial peptidoglycan (PGN) and bacterial lipoproteins (BLP), are called pathogen-associated molecular patterns (PAMPs). PAMPs are sensed by pattern recognition receptors (PRRs), which include CD14 and various Toll-like receptors (TLRs). LPS is recognized following its binding to lipoprotein binding protein (LBP). CD14, is part of the LPS receptor complex, and together with the functionally linked TLR2 and TLR4, and the associated molecule MD-2 (lymphocyte antigen 96) are expressed in the endocrine cells of human pancreatic islets. PRRs and TLRs signaling pathways play a major role in maintaining pathogen-free host tissues. When TLRs are activated by PAMPs, through NFκB signaling the innate and adaptive immune systems are activated. Invading bacteria are killed by the terminal attack complex (MAC) of the classical complement pathway and by specific anti-bacterial antibodies provided by the adaptive immune system.