The present study is the first to describe the existence and persistence of IgE anti H1N1 influenza virus antibodies in human sera obtained during and after the pandemic influenza H1N1 phase. Here we report the presence of IgE anti-H1N1 antibodies (as well as IgG anti-H1N1) antibodies in the serum of patients infected with H1N1 during the 2009 pandemic and in serum from the same patients up to 12 months following infection (Western blotting). Because our infected H1N1 patients were also previously vaccinated with influenza A virus vaccine, the H1N1 enzyme-linked immunosorbent assay which we prepared displayed pre-existing cross-reactive influenza A virus-specific responses with the H1N1 virus antigen, thus necessitating us to separate (and compare) the viral protein components from H1N1 influenza virus and seasonal influenza A virus on polyacrylamide gel. Earlier studies reported by other investigators13
have used polyacrylamide gel electrophoresis to compare the structural proteins of the A/Havana/1292/78 national strain with the proteins of three international strains in relation to protein structure (surface antigens).13
The authors reported that the most abundant protein in the four strains was M protein, while other differences between the Cuban strain and the three international strains were not observed.13
In our study, we found that the serum of vaccinated and infected children and adults contained IgE and IgG antibodies to both H1N1 and influenza virus, with strong IgE and IgG band intensity at 56 kDa. Interestingly, in subjects who were vaccinated but not infected, band intensity at 56 kDa was lowered by about 35%–50%. These results suggest augmented IgE and IgG antibody responses to influenza A H1N1 with respect to the vaccinated and infection states. Although there may exist antigenic mimicry to certain components of the virus which are shared in the immune response to vaccination as well as infection, the demonstration of increased virus-specific responses following vaccination in the presence of infection compared with vaccination alone, in the presence of our fractionated protein assay, suggests unique responses to each of these viral strains in their own right. Because the laboratory diagnosis of clinical H1N1 infection differs between laboratories, the uniqueness of epitopes among influenza strains and preparations remains unclear. Future studies utilizing manufacturer’s preparations are warranted to elucidate precisely which antigens are more versus less immunogenic with respect to isotype as well as idiotype.
However, of notable, interest, is the fact that both H1N1-infected patients had low serum IgE levels. Taken together, these results suggest that the total serum IgE level is not as important as the specific fraction of IgE anti-H1N1 influenza antibodies representing a percentage of the total IgE responsible for mediating IgE anti-viral immune responses, and levels of serum IgE do not necessarily correlate with virus-specific IgE. The active role of IgE in viral disease is unknown but in earlier preliminary observations14
and other studies1
we have suggested that the IgE molecule has evolved to have other beneficial functions, including those of an antiviral nature.
Other studies in our laboratory have investigated the role of IgE in other disease states, ie, anticancer antibodies, which were found in patients with normal and high serum IgE levels and had the ability to mediate antibody-dependent cell-mediated cytotoxicity against cancer cells in vitro.15
Similarly, in the present study, these specific immune responses did not correlate with total serum IgE levels.15
Some limitations in the design of this study should be borne in mind, including its small sample size and ethnic homogeneity, and any generalizations should be made cautiously. However, the strengths of this research include demonstration of the selectivity and specificity of antiviral IgE responses to viruses which maintain some degree of shared antigenicity (influenza versus H1N1) and further supports the uniqueness of antiviral IgE responses. To this end, the distinct and independent regulation of IgE in viral pathogenesis (ie, HIV and varicella zoster virus) as distinct from other immunoglobulin isotypes (IgM, IgG, and IgA) has also been reported.5
Studies reported by Ferrazzi et al16
have shown that although adult HIV-1 infected individuals often exhibit hypergammaglobulinemia, the relative increase in serum IgE levels is greater than that of other serum immunoglobulins, with elevation especially apparent in end-stage disease (ie, acquired immune deficiency syndrome) in patients with decreased numbers of blood CD4+ T cells (<200/mm3
However, it is well established that T cell responses play a role during the early stage of viral infection.17
Thus, future experiments are warranted to quantify the H1N1 influenza A virus-specific T cell response(s) in combination with humoral responses.
To our knowledge, this study is the first to describe the presence and persistence of IgE anti-H1N1 influenza virus antibodies in serum from human subjects previously infected with H1N1 influenza virus during the 2009 pandemic. Although additional studies are required for further elucidation of the possible molecular mechanisms involved, our results raise the possibility that IgE could be used as a novel biomarker for human viral disease and that IgE may have a possible functional role in virus memory responses and the pathogenesis of viral disease.