Several immune-related molecules in penaeid shrimps have been discovered, most of these via the
analysis of expressed sequence tag libraries, microarray studies and proteomic approaches. These
immune molecules include antimicrobial peptides, serine proteinases and inhibitors, phenoloxidases,
oxidative enzymes, clottable protein, pattern recognition proteins, lectins, Toll receptors, and other
humoral factors that might participate in the innate immune system of shrimps. These molecules have
mainly been found in the hemolymph and hemocytes, which are the main sites where immune reactions
take place, while some are found in other immune organs/tissues, such as the lymphoid organs, gills and
intestines. Although the participation of some of these immune molecules in the shrimp innate immune
defense against invading pathogens has been demonstrated, the functions of many molecules remain
unclear. This review summarizes the current status of our knowledge concerning the discovery and
functional characterization of the immune molecules in penaeid shrimps