title: Outer membrane protein A (OmpA) of Shigella flexneri 2a links innate and adaptive immunity in a TLR2-dependent manner and involvement of IL-12 and nitric oxide.
abstract: We determine that OmpA of Shigella flexneri 2a is recognized by TLR2 and consequently mediates the release of proinflammatory cytokines and activates NF-κB in HEK 293 cells transfected with TLR2. We also observe that in RAW macrophages TLR2 is essential to instigate the early immune response to OmpA via NF-κB activation and secretion of cytokines and NO. Consistent with these results, TLR2 knockdown using siRNA abolishes the initiation of immune responses. Processing and presentation of OmpA depend on TLR2; MHCII presentation of the processed antigen and expression of CD80 significantly attenuated in TLR2 knockdown macrophages. The optimum production of IFN-γ by the macrophages:CD4(+) T cells co-culture depends on both TLR2 activation and antigen presentation. So, TLR2 is clearly recognized as a decisive factor in initiating host innate immune response to OmpA for the development of CD4(+) T cell adaptive response. Furthermore, we demonstrate in vivo that intranasal immunization of mice with OmpA selectively enhances the release of IFN-γ and IL-2 by CD4(+) T cells. Importantly, OmpA increases the level of IFN-γ production in Ag-primed splenocytes. The addition of neutralizing anti-IL-12p70 mAb to cell cultures results in the decreased release of OmpA-enhanced IFN-γ by Ag-primed splenocytes. Moreover, coincubation with OmpA-pretreated macrophages enhances the production of IFN-γ by OmpA-primed CD4(+) T cells, representing that OmpA may enhance IFN-γ expression in CD4(+) T cells through the induction of IL-12 production in macrophages. These results demonstrate that S. flexneri 2a OmpA may play a critical role in the development of Th1 skewed adaptive immune response.
authors.affiliation: Division of Pathophysiology, National Institute of Cholera and Enteric Diseases, P-33, C.I.T. Road, Scheme-XM, Beliaghata, Kolkata 700010, West Bengal, India.
authors.forename: Debasis
authors.initials: D
authors.lastname: Pore
authors.forename: Nibedita
authors.initials: N
authors.lastname: Mahata
authors.forename: Manoj K
authors.initials: MK
authors.lastname: Chakrabarti
mesh_terms: D056704:Adaptive Immunity; D000818:Animals; D017951:Antigen Presentation; D001425:Bacterial Outer Membrane Proteins / Q000276:immunology*; D004789:Enzyme Activation; D005260:Female; D057809:HEK293 Cells; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000378:metabolism; D054884:Host-Pathogen Interactions; D006801:Humans; D007113:Immunity, Innate; D007371:Interferon-gamma / Q000096:biosynthesis; D018664:Interleukin-12 / Q000378:metabolism / Q000502:physiology*; D053712:Interleukin-12 Receptor beta 2 Subunit / Q000235:genetics / Q000378:metabolism; D008213:Lymphocyte Activation; D008264:Macrophages / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D016328:NF-kappa B / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D010766:Phosphorylation; D051571:Protein Kinase C-alpha / Q000378:metabolism; D021381:Protein Transport; D019707:Receptors, Chemokine / Q000378:metabolism; D012763:Shigella flexneri / Q000276:immunology / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D001425:Bacterial Outer Membrane Proteins; D000949:Histocompatibility Antigens Class II; D053712:Interleukin-12 Receptor beta 2 Subunit; D016328:NF-kappa B; D019707:Receptors, Chemokine; C493486:Tlr2 protein, mouse; D051195:Toll-Like Receptor 2; C078167:OMPA outer membrane proteins; D018664:Interleukin-12; D009569:Nitric Oxide; D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D051571:Protein Kinase C-alpha