Cellular and humoral components of innate immunity in Squilla mantis (Crustacea, Stomatopoda): a preliminary approach.

The morphology and enzyme content of circulating cells of the mantis shrimp Squilla mantis from the North Adriatic Sea, together with their ability to phagocytize foreign cells, were studied for deeper insights into the function of crustacean hemocytes in immune responses. The enzyme content and the agglutinating and hemolytic activities of cell-free hemolymph were also assayed. Three hemocyte types, i.e., hyalinocytes, semigranulocytes and granulocytes, were distinguished, according to cell and nuclear morphology and the presence of cytoplasmic granules, in agreement with previous reports. All of them share the same patterns of enzyme activities and are recognized by the same lectins. Spreading cells (hyalinocytes and semigranulocytes) can ingest foreign cells; granules of semigranular and granular cells have similar cytochemical properties. Injection of Micrococcus luteus into the heart sinus results in an increase in the frequency of hyaline cells and a decrease in the frequency of granulocytes. After 24 h from the injection, a decrease in the number of phagocytizing hyalinocytes, and a general decrease in the frequency of acid phosphatase-positive cells was reported. The above results suggest the existence of a single differentiation pathway for Squilla haemocytes with the three hemocyte morphs as different stages of cell differentiation. Results also indicate that Squilla hemolymph performs immunosurveillance, through rapid changes in hemocyte distribution, increase of antimicrobial and antioxidant enzymes and secretion of lectins stimulating agglutination, phagocytosis and encapsulation.