Involvement of HAb18G/CD147 in T cell activation and immunological synapse formation.

HAb18G/CD147, a glycoprotein of the immunoglobulin super-family (IgSF), is a T cell activation-associated molecule. In this report, we demonstrated that HAb18G/CD147 expression on both activated CD4(+) and CD8(+) T cells was up-regulated. In vitro cross-linking of T cells with an anti-HAb18G/CD147 monoclonal antibody (mAb) 5A12 inhibited T cells proliferation upon T cell receptor stimulation. Such co-stimulation inhibited T cell proliferation by down-regulating the expression of CD25 and interleukin-2 (IL-2), decreased production of IL-4 but not interferon-γ. Laser confocal imaging analysis indicated that HAb18G/CD147 was recruited to the immunological synapse (IS) during T cell activation; triggering HAb18G/CD147 on activated T cells by anti-HAb18G/CD147 mAb 5A12 strongly dispersed the formation of the IS. Further functional studies showed that the ligation of HAb18G/CD147 with mAb 5A12 decreased the tyrosine phosphorylation and intracellular calcium mobilization levels of T cells. Through docking antibody-antigen interactions, we demonstrated that the function of mAb 5A12 is tightly dependent on its specificity of binding to N-terminal domain I, which plays pivotal role in the oligomerization of HAb18G/CD147. Taken together, we provide evidence that HAb18G/CD147 could act as a co-stimulatory receptor to negatively regulate T cell activation and is functionally linked to the formation of the IS.