A Novel Role for Non-Neutralizing Antibodies against Nucleoprotein in Facilitating Resistance to Influenza Virus

Abstract

Current influenza vaccines elicit Abs to the hemagglutinin and neuraminidase envelope proteins. Due to antigenic drift, these vaccines must be reformulated annually to include the envelope proteins predicted to dominate in the following season. By contrast, vaccination with the conserved nucleoprotein (NP) elicits immunity against multiple serotypes (heterosubtypic immunity). NP vaccination is generally thought to convey protection primarily via CD8 effector mechanisms. However, significant titers of anti-NP Abs are also induced, yet the involvement of Abs in protection has largely been disregarded. To investigate how Ab responses might contribute to heterosubtypic immunity, we vaccinated C57BL/6 mice with soluble rNP. This approach induced high titers of NP-specific serum Ab, but only poorly detectable NP-specific T cell responses. Nevertheless, rNP immunization significantly reduced morbidity and viral titers after influenza challenge. Importantly, Ab-deficient mice were not protected by this vaccination strategy. Furthermore, rNP-immune serum could transfer protection to naive hosts in an Ab-dependent manner. Therefore, Ab to conserved, internal viral proteins, such as NP, provides an unexpected, yet important mechanism of protection against influenza. These results suggest that vaccines designed to elicit optimal heterosubtypic immunity to influenza should promote both Ab and T cell responses to conserved internal proteins.

Vaccination inducing broad and improved cross protection against multiple subtypes of influenza A virus

“…In contrast, M2 VLP supplemented vaccination induced strong cross-reactive binding antibodies to virions of different subtypes. Nonneutralizing anti-influenza humoral immunity was shown to confer protection (17,18) and to be dependent on opsonophagocytosis of influenza virions by macrophages (15). It was recently reported that monoclonal antibodies binding to multimeric M2 peptides were more protective than antibodies binding to monomeric M2 peptide (19).…”

“…Multiple mechanisms might be involved in conferring protection by nonneutralizing antibodies (16,17,20). DCs and macrophage cells might play a role in mediating cross-protection provided by nonneutralizing antibodies.…”

Characterization of Influenza H5N1 Nucleocapsid Protein for Potential Vaccine Design

“…A band with an electrophoretic mobility consistent with protein of a molecular size of 60 kDa (which accurately compared with the molecular weight of 56 kDa for the expected (His) 6 -tagged NP) was routinely observed in all preparations. Identity of the band was confirmed by Western blot analysis using anti-NP antibody (Figure 1(b)).…”

“…NP has also been shown to stimulate a cytotoxic T lymphocyte response in both human and mice, resulting in quicker viral clearance and faster recovery from influenza infection [5]. Studies also demonstrate that NP can induce substantial titres of anti-NP antibodies which, while not neutralizing, were capable of increasing viral clearance and conferring hetero-subtypic immunity [6][7][8]. In addition, because NP is relatively conserved across all known influenza strains and has low sequence drift rate [9,10], vaccines based on NP might be effective against most influenza strains, thereby eliminating the necessity of annual production.…”

“…The first is the discovery of the biologic which elicits the desired therapeutic response. Several groups seem to believe that NP satisfies this criterion [6][7][8]. The second and equally important aspect in vaccine development is the translation of that biologic into a formulation which, while appropriate for both safe injection and bio-distribution, also confers stability, giving the product an acceptable shelf life [11].…”