Role of Tachylectins in Host Defense of the Japanese Horseshoe Crab Tachypleus Tridentatus

Immunity to pathogens is mediated by two general systems, innate and acquired immunity. Acquired immunity is found only in vertebrates and it is the system of B and T lymphocytes, which produces a multitude of specific antigen receptors and antibodies by somatic gene rearrangement. Innate immunity is phylogenetically older than acquired immunity and is present in all multicellular organisms. These proteins pre-exist in hosts, or are rapidly induced within hours of infection. With this immunity polysaccharides or other substances on pathogens are detected through pattern recognition (1,2). The innate immunity of invertebrates is triggered by polysaccharide derivatives, such as lipopolysaccharides (LPS), proteoglycans, and (β-1,3-glucans. Examples are hemolymph coagulation in horseshoe crabs (3–5) and phenoloxidasemediated melanization in crustaceans and insects (6).