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Document Type

Book Chapter


Virginia Institute of Marine Science


Fisher, William S., ed

Publication Date


Book Title

Disease Processes in Marine Bivalve Molluscs


American Fisheries Society


Bethesda, Maryland


American Fisheries Society Special Publication 18


Natural humoral components have been discovered and described in hemolymph from several marine bivalve species including eastern oyster Crassostrea virginica, blue mussel Mitilus edulis, northern quahog Mercenaria mercenaria, softshell Mya arenaria, and Pacific oyster Crassostrea gigas, These hemolymph components are enzymes of lysosomal origin, agglutinins, lectins, hemolysin, and antimicrobial substances, These components are proteins or glycoproteins found in the serum, hemocytes, or both, The exact relationship of these substances to the internal defense of marine bivalves against parasites and pathogenic microorganisms is not known. Lysosomal enzymes seem to have a double role, defense and nutrition. The free- and cell-bound lectins and agglutinins are believed to serve as recognition factors for the attachment of nonself particles to the phagocytes. The nature of bivalve hemolymph components appears to be innate and nonspecific. It has been suggested that the elevation in titer of enzymes of lysosomal origin in bivalve hemocytes and hemolymph after antigenic challenge is the acquired "humoral" protection produced by the animal. As yet, no experimental evidence has been obtained to support this idea. Whether humoral factors can be acquired in oysters and other marine bivalves needs further investigation. The specificity and the function of humoral factors relating to internal defense remain to be determined. Several mechanisms have been hypothesized for humoral defense in invertebrates. In these hypothesized mechanisms, recognition sites presented on the hemocytes are proposed for the events of phagocytosis, encapsulation, hypersynthesis and release of lysosomal enzymes.

Humoral Defense Factors in Marine Bivalves