title: Synergy between the classical and alternative pathways of complement is essential for conferring effective protection against the pandemic influenza A(H1N1) 2009 virus infection.
abstract: The pandemic influenza A(H1N1) 2009 virus caused significant morbidity and mortality worldwide thus necessitating the need to understand the host factors that influence its control. Previously, the complement system has been shown to provide protection during the seasonal influenza virus infection, however, the role of individual complement pathways is not yet clear. Here, we have dissected the role of intact complement as well as of its individual activation pathways during the pandemic influenza virus infection using mouse strains deficient in various complement components. We show that the virus infection in C3-/- mice results in increased viral load and 100% mortality, which can be reversed by adoptive transfer of naïve wild-type (WT) splenocytes, purified splenic B cells, or passive transfer of immune sera from WT, but not C3-/- mice. Blocking of C3a and/or C5a receptor signaling in WT mice using receptor antagonists and use of C3aR-/- and C5aR-/- mice showed significant mortality after blocking/ablation of C3aR, with little or no effect after blocking/ablation of C5aR. Intriguingly, deficiency of C4 and FB in mice resulted in only partial mortality (24%-32%) suggesting a necessary cross-talk between the classical/lectin and alternative pathways for providing effective protection. In vitro virus neutralization experiments performed to probe the cross-talk between the various pathways indicated that activation of the classical and alternative pathways in concert, owing to coating of viral surface by antibodies, is needed for its efficient neutralization. Examination of the virus-specific complement-binding antibodies in virus positive subjects showed that their levels vary among individuals. Together these results indicate that cooperation between the classical and alternative pathways not only result in efficient direct neutralization of the pandemic influenza virus, but also lead to the optimum generation of C3a, which when sensed by the immune cells along with the antigen culminates in generation of effective protective immune responses.
authors.affiliation: National Centre for Cell Science, S. P. Pune University Campus, Ganeshkhind, Pune, India.
authors.forename: Ajitanuj
authors.initials: A
authors.lastname: Rattan
authors.affiliation: Microbial Containment Complex, National Institute of Virology, Pune, India.
authors.forename: Shailesh D
authors.initials: SD
authors.lastname: Pawar
authors.affiliation: National Centre for Cell Science, S. P. Pune University Campus, Ganeshkhind, Pune, India.
authors.forename: Renuka
authors.initials: R
authors.lastname: Nawadkar
authors.affiliation: National Centre for Cell Science, S. P. Pune University Campus, Ganeshkhind, Pune, India.
authors.forename: Neeraja
authors.initials: N
authors.lastname: Kulkarni
authors.affiliation: National Centre for Cell Science, S. P. Pune University Campus, Ganeshkhind, Pune, India.
authors.forename: Girdhari
authors.identifier: 0000-0002-3799-3603
authors.initials: G
authors.lastname: Lal
authors.affiliation: Microbial Containment Complex, National Institute of Virology, Pune, India.
authors.forename: Jayati
authors.identifier: 0000-0002-8572-2867
authors.initials: J
authors.lastname: Mullick
authors.affiliation: National Centre for Cell Science, S. P. Pune University Campus, Ganeshkhind, Pune, India.
authors.forename: Arvind
authors.identifier: 0000-0003-1664-2422
authors.initials: A
authors.lastname: Sahu
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D000914:Antibodies, Viral / Q000276:immunology; D003170:Complement Pathway, Alternative / Q000276:immunology*; D003171:Complement Pathway, Classical / Q000276:immunology*; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009500:Neutralization Tests; D009976:Orthomyxoviridae Infections / Q000276:immunology*
chemical_list: D000914:Antibodies, Viral