The molecular basis of innate immunity in the horseshoe crab.

During the past two decades, the molecular structures and functions have been established for various defense molecules, using horseshoe crab (Limulus) as a model animal. These defense molecules include clotting factors, proteinase inhibitors, lectins, antimicrobial peptides and other humoral factors found mainly in the hemolymph. These components of the cellular and humoral systems, which together comprise innate immunity, defend horseshoe crab effectively from invading microbes.