The response of mRNA expression upon secondary challenge with Vibrio anguillarum suggests the involvement of C-lectins in the immune priming of scallop Chlamys farreri.

The enhanced immunity against a second encounter with the particular pathogen has suggested the presence of "immune priming" in scallop. In the present study, the survival rate and expression patterns of five C-lectin isoforms from scallop Chlamys farreri were explored after "vaccination" of heat-killed Vibrio anguillarum or successively challenge with V. anguillarum and Micrococcus luteus. When scallops were challenged with live bacteria, the survival rate increased significantly only in the group firstly "vaccinated" with inactivated V. anguillarum and then challenged with live V. anguillarum compared with naive scallops (from 41% to 63.6%, P<0.05), showing enhanced protective effects of inactivated bacteria with "specificity". When scallops received the challenge with V. anguillarum, the mRNA expression level of five C-lectins in scallops which were immuned previously with heat-killed V. anguillarum peaked significantly higher (26.7-, 121.7-, 60.1-, 27.4-, 16.3-fold to 0h, respectively, P<0.01) than that in non-immuned scallops (7.6-fold, P<0.05; 6.4-, 3.9-fold, P>0.05; 5.7-fold, P<0.05; 11.7-fold, P<0.01, to 0h, respectively). A significantly higher peak and 3-9h earlier response of all C-lectins mRNA expression were observed after challenge with live V. anguillarum (26.7-, 121.7-, 60.1-, 26.4- and 16.3-fold to 0h, respectively, P<0.01), compared with those only received first injection with heat-killed V. anguillarum (1.6-fold, P>0.05; 8.3-fold, P<0.05; 5.2-fold, P>0.05; 14.5-fold, P<0.01; 4.3-fold, P>0.05, to 0h, respectively). The response of mRNA expression to the secondary encounter with the same bacteria was stronger than that of successively encounter with the different class of bacteria. It was obvious that the mRNA expression of C-lectins in scallops was significantly enhanced by the successive challenge of same species of bacteria with a certain degree of specificity. All the results suggested that C-lectins might be involved in some form of immune priming, and it might provide new insights into mechanism of invertebrate immune priming.