Monoclonal antibodies targeting the synthetic peptide corresponding to the polybasic cleavage site on H5N1 influenza hemagglutinin

Monoclonal antibodies (mAb) specific to the synthetic peptide of hemagglutinin polybasic cleavage site of H5N1 virus were raised and tested for their neutralizing potential.Purified mAb showed suppression of H5N1 pseudovirus infection on Madin-Darby Canine Kidney (MDCK) cells but the efficacy was less than 50%. Since those mAb are specific to the intact uncut polybasic cleavage site of hemagglutinin, their efficacy depends on the extent of hemagglutinin cleavage on the viral surface.Proteolytic analysis suggests the low efficacy associated with those mAb may be due to proteolytic cleavage already present on the majority of hemagglutinin prior to the infection of virus.Avian H5N1 highly pathogenic influenza virus was first isolated from sick geese in China during 1996 and later transmitted to human in Hon Kong during 1997 [1]. This H5N1 virus was spread throughout Asia and over as far as Europe or Africa by migratory birds in 2005 [1], which prompted a fear of global pandemic. Avian H5N1 Influenza virus has two major antigenic surface proteins, hemagglutinin (HA) and neuraminidase (NA), and a RNA genome which accumulates mutations rapidly over its life cycles [2]. The rapid accumulation of genomic mutations results in frequent alterations on the surface epitopes that is known as antigenic drift [3]. The function of HA is to recognize host sialic acid residue as an entry receptor [4,5], and to fuse viral envelope with vesicle's membrane [5,6] after the linker peptide between subdomain HA1 and HA2 of HA is cleaved by host trypsin-like proteases. Virulent H5 and H7 hemagglutinins [7] have a polybasic cleavage site that is exposed and cleavable by furin or other proprotein convertases [8,9] which enables the virus to infect multiple organs and leads to multisystem failure [7]. A second factor correlating to the high pathogenicity of H5N1 influenza virus is the PB2 subunit in polymerase complex [10,11]. The adaptation of viral polymerase complex to replicate in mammalian