Detection of two lectins in haemolymph from the oyster Pinctada maxima

Isolation and partial characterization of a calcium-dependent lectin (chiletin) from the haemolymph of the flat oyster, Ostrea chilensis

A calcium-dependent lectin (chiletin) was isolated from oyster haemolymph by mannose elution from Sepharose CL-6B followed by anion exchange chromatography. Chiletin was predominantly composed of 12 and 24 kDa bands when examined with SDS-PAGE under reducing and non-reducing conditions, respectively. Larger molecular weight bands of 36 and 50 kDa were also variably present under reducing conditions. The NH2-terminal sequence of the 24 kDa band was determined and was not homologous to any known protein from the databases searched. Isolated chiletin was composed of multiple isomers approximately 12 kDa in size and ranging in pI from 5.2 to 6.0. Rabbit antiserum was raised to a synthetic peptide coupled to keyhole limpet hemocyanin and the size of the chiletin subunits was confirmed by Western blot. Two and five different conformational aggregates of chiletin were resolved in oyster haemolymph using size exclusion chromatography in 8 M urea and PBS, respectively. The largest aggregate obtained from size exclusion in 8 M urea was estimated to be greater than 640 kDa. The ability of whole haemolymph and isolated chiletin to agglutinate sheep red blood cells was inhibited by galactose and mannose. Chiletin was identified by immunohistochemistry to be most consistently present in the auricle, followed by the digestive gland, however staining was seen sporadically in haemocytes, gastrointestinal epithelium and interstitial connective tissue cells.

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).