An integrin alpha 4 (ChIntα 4) from oyster Crassostrea hongkongensis mediates the hemocytes phagocytosis towards Vibrio alginolyticus

Integrins, a family of cell adhesion transmembrane receptors, mediate cell adhesion, migration, proliferation, apoptosis, and phagocytosis. In the present study, an integrin ChIntα 4 from Crassostrea hongkongensis was characterized to investigate its role in defensing against pathogenic bacterium Vibrio alginolyticus. The full-length cDNA sequence of ChIntα 4 was 3572 bp with an open reading frame (ORF) of 3168 bp, which encoded a polypeptide with 1055 amino acids. The mRNA expression of ChIntα 4 in the hemocytes was significantly up-regulated at 6 h and 24 h post V. alginolyticus stimulation (p < 0.01). The recombinant ChIntα 4 protein could agglutinate the rabbit red blood cells and Gram-negative bacteria V. alginolyticus and Escherichia coli. Moreover, the phagocytic activity of the hemocytes was significantly down-regulated from 46.9% to 32.7% when blocked with anti-ChIntα 4 antibody, and it was significantly up-regulated from 42.7% to 59.5% post transfection with pCI-neo-ChIntα 4 plasmid (p < 0.05). In conclusion, these findings demonstrated that ChIntα 4 might be involved in resisting V. alginolyticus infection and regulating phagocytosis as a cell adhesion receptor in C. hongkongensis.