| Abstract: | The function of blood is to deliver nourishments to and remove wastes from all parts of the body. It is made up of different kinds of cells bathed in a fluid called plasma. The major cellular components of blood include (1) red blood cells for carrying oxygen to the various tissues, (2) white blood cells for providing defense against infectious agents and cancer, and (3) platelets for inducing a cascade of events leading to blood clot formation that stops bleeding. The plasma also contains numerous proteins for maintaining normal balance in our body, and include (1) clotting factors such as factor VIII, factor IX, fibrinogen, and thrombin, (2) protease inhibitors and anticoagulants that regulate the coagulation pathway, the complement system, or the fibrinolytic system, (3) immunoglobulin which are antibodies directed against different infectious agents, and (4) albumin which functions as a volume expander to maintain our blood volume and is essential when threatened with severe blood loss. The plasma of the invertebrate horseshoe crab, contains three major proteins: hemocyanin, C-reactive protein (CRP), and α2-macroglobulin. Hemocyanin functions as an oxygen-carrying protein. CRP is a lectin that binds to phosphocholine of the pneumococcus C-polysaccharide, to the chromatins of damaged cells, and to the galactose moiety of desialylated glycoprotein as a membrane-associated protein on liver marcrophages. CRP exists, however, as a normal component of the invertebrate hemolymph. α2-macroglobulin exhibits proteinase inhibitory activity with a broad specificity that can block the activities of protease secreted from invading microorganisms. The Limulus CRP, along with the C3 homologue α2-macroglobulin, participates in a complement - like hemolytic activity in horseshoe crab hemolymph. Whereas the vertebrate evolved to use both the innate and the adaptive immunity, the invertebrate only uses the innate immunity. The innate immunity uses germ-line encoded receptors to recognize conserved molecular constituents of infectious microorganisms, is phylogenetically older, with some of its form presumably presents in all multicellular organisms. The adaptive immunity is mediated by highly specific antigen receptors that are distributed clonally on the two types of lymphocytes, the T-cells and the B-cells. Evidence has accumulated in recent years to suggest that the innate immune system provides signals that are essential for the adaptive immune response to generate information on the origin of the antigen and the type of response to be induced. This linkage invites renewed interest in the study of the innate immune system of the horseshoe crab. |
