A novel surface marker CD49d promotes TNF expression in oyster agranulocytes by mediating the MAPK pathway.

CD49d, encoded by the gene Integrin α4, is a significant member of cell adhesion receptors, which is widely expressed in various immune cells to trigger immune responses against invading pathogens. In the present study, the expression of Cg CD49d and its regulatory role in TNF expression were investigated in the Pacific oyster Crassostrea gigas. There were five Int-alpha domains, an Integrin_alpha2 region and a unique FG-GAP repeat region inserted identified in Cg CD49d. Cg CD49d transcript was specifically expressed in haemocytes, and its mRNA expression level in haemocytes increased after LPS and Vibrio splendidus stimulation. After Cg CD49d was blocked by using its antibody, the phosphorylation level of Cg JNK in the MAPK signaling pathway and Cg TNF transcripts decreased significantly post V. splendidus stimulation. After phosphorylation level of Cg JNK was inhibited by using its inhibitor, the nuclear translocation of Cg Rel was restrained and Cg TNF transcripts also decreased significantly post V. splendidus stimulation. Furthermore, Cg CD49d was found to be mainly expressed in the agranulocyte subpopulation, and Alexa Fluor 488-conjugated Cg CD49d antibody labeled agranulocytes with a circle of green fluorescence signals on Cg CD49d+ agranulocyte surface under Confocal microscopy, which accounted for 24.9 ± 4.53% of total haemocytes. Collectively, these results suggested that Cg CD49d promoted TNF expression in oyster haemocytes against bacterial invasion by mediating MAPK pathway, and it could be used as a surface marker to type and sort a subset of agranulocyte subpopulation among haemocytes. [Display omitted] • Cg CD49d was highly expressed in agranulocytes of oyster haemocytes. • Cg CD49d was involved in regulating Cg TNF expression via MAPK signaling pathway. • Cg CD49d+ agranulocytes accounted for 24.9 ± 4.53 % of haemocytes. [ABSTRACT FROM AUTHOR]