CD9 and infection: In order to investigate the role of tetraspanins in B. pseudomallei infection, we used monoclonal antibodies (MAbs) specific to the large extracellular EC2 domain of tetraspanins and recombinant EC2 proteins of CD9, CD63, and CD81 to pretreat a human epithelial cell line A549 and a mouse macrophage cell line J774A.1 before infection.