Porcine FcγRⅢ And Its Role In Antibody-dependent Enhencement Of PRRSV Infection

IgG Fc receptors (FcyRs), which are widely distributed on the surface of well-known immune cells, are an important family of receptor molecules. They can bind with the immunoglobulin G (IgG) fragments specifically, providing a link between cell-mediated immune and humoral immune response, and play a key role in the body's immune defense system. The latest study revealed that FcyRs are also ideal drug targets in treating allergic and autoimmune diseases, in that their important immune function in regulating positive and negative cell response.In recent few years, research on livestock FcyRs has made great progress. The FcyRs genes in main livestock species have been cloned and the biologically functions were characterized. Porcine FcyRs are consisted of three types of molecules, such as FcyRI (CD64), FcyRII (CD32) and FcyRIII(CD16). FcyRIII is a kind of 50-80 kD glycoprotein expressed on the membrane of alveolar macrophges cells, mast cells and polymorphnuclear (PMN) cells. The porcine FcyRIIIA complex are 45 kDa glycoprotein on the PMN cells, and their intracellular domains always connect with FcR y chain or other subunits. So the in vitro expression of FcyRIIIA complex on membrane must depend on the co-transfection of FcyRIIIA and FcR y chain genes.Porcine reproductive and respiratory syndrome (PRRS) is an infectious viral disease caused by PRRSV and characterized by the abortion of pregnant sow and breathing obstacle of pig. Recent years, the infection and spread of virulent strain of PRRSV has caused great damage to the farming of swine all over the world. Antibody dependent enhancement (ADE) is a key impediment for developing efficient vaccine.To investigate the molecular mechanism of ADE, two eukaryotic expression plasmid containing FcyRIII and FcRy chain genes were individually constructed and co-transfected into Marc-45 cells. The Mar-45 cells which can stably expressed FcyRâ…¢complex were selected and cloned by the bi-antigenic against hygromycin B and G418. When the cloned Marc-145 cells was infeted with BJ-4, the well-known standard strain of PRSSV and the 1:1600-diluted anti-PRRSV IgG mixture, more virus was harvested than the control group without IgG. This indicated that FcyRIII complex could mediate ADE in the infection of PRSSV. In the study, the preliminary molecular mechanism of ADE was investigated by studying the interaction of PRRSV and FcyRs. The result not only provided theoretical basis for new vaccine, immune adjuvant and anti-virus drugs, but also help to search for other pathogenic mechanisms of important diseases.