Some research advances of immune mechanism during infection in China

Yang, Wei

The first defense employed by the innate immune response is to recognize molecular patterns expressed by invading pathogens via pattern recognition receptors (PRRs). Proteins on pathogens which are involved in driving host immune response are defined. The surface glycoprotein hemagglutinin (HA), the most important protein in molecular epidemiology and pathogenesis of influenza viruses, is characterized in the swine-origin influenza virus A (H1N1)-2009 [1]. Tp0751 recombinant protein from T. pallidum is found to induce the production of proinflammatory cytokines and the ensuing immune responses [2] . The PRRs may locate either on the membrane surface e.g. Toll-like receptors (TLRs) or inside the cytoplasm e.g. Nod-like receptors (NLRs). NLRs assemble into multimolecular machines termed inflammasomes to detect intracellular pathogens [3] . Inflammasomes drive inflammatory processes through promoting the maturation of inflammatory cytokines such as interleukin (IL)-1 and IL-18 [4-7]. Alternatively, the recognition of lipopolysaccharide (LPS) is mainly mediated by TLR4/myeloid differentiation protein-2 (MD-2) heterodimers. During this process, residues Glu24-Met41 in the N terminal of TLR4 are involved in TLR4 binding to MD-2 and LPS-stimulated TLR4 aggregation [8] . Signaling pathways initiated by ligand binding to TLRs activate NF-B, Mitogen-activated protein kinase (MAPK), and interferon (IFN), during in which the tumor necrosis factor (TNF) receptor-associated factor (TRAF) family is shown to participate [9-11]. These responses triggered by PRRs recognizing pathogens culminate activation of antimicrobial killing mechanisms and secretion of cytokines and chemokines. For example, production of broadspectrum antimicrobial peptides is a common innate immunity defense mechanism against infection. As potentially great alternatives to current antibiotics, antimicrobial peptides have been studied in most researches [12] [13] [14] [15] [16] [17] . Chen and colleagues have first isolated antibacterial peptides from the ovine reproductive tract [18] . Two novel temporins, one of important families of antimicrobial peptides from Litho-bates catesbeianus, have been molecular cloned [19] . The antimicrobial mechanism of these peptides has been investigated. Due to the critical role of type I IFNs in innate antiviral response, their production and downstream signaling cascades are often the hot topics under intensive investigation. Plasmacytoid dendritic cells (pDCs), which sense viral nucleic acids within the endosomal compartments through their TLR7 and TLR9, are professional type I IFN-producing cells. These IFNs not only directly inhibit viral replication but also play an essential role in linking the innate and adaptive immune system [20] . The Mx GTPase pathway is one of the most powerful antiviral mechanisms induced by IFNs. Belonging to the dynamin superfamily of large GTPases, Mx proteins have direct antiviral activity by interfering with viral genome replication [21] [22] [23] . Sun and colleagues have well reviewed recent findings in the structural and functional studies of Mx protein, which are significant for prophylaxis and control of the emerging and re-emerging viruses [24] .