Agglutination of bacteria and erythrocytes by serum from six species of marine molluscs.

Lectins have been implicated as recognition molecules in the invertebrate immune response, yet their capacity to recognize (agglutinate and/or opsonize) potentially invasive microorganisms is largely unknown. In this study, sera from six species of marine molluscs (oyster, clam, octopus, squid, cuttlefish, and sea hare) were found to agglutinate 64 of 94 bacterial isolates (15 genera, 36 species) and seven types of vertebrate erythrocytes. Oyster, clam, and octopus sera agglutinated the greatest number of bacterial isolates and oyster serum exhibited the highest intensity and titer of agglutination. Agglutination was isolate dependent, implying high lectin specificity. Titers were highly variable for wild populations of oysters and sea hares and relatively constant for F4-generation cuttlefish reared in aquaculture systems. Simultaneous agglutination of specific bacterial isolates indicated conservation of lectin specificity between oyster and clam sera (bivalves) and between squid and cuttlefish sera (cephalopods).