Induction and maintenance of anti‐influenza antigen‐specific nasal secretory IgA levels and serum IgG levels after influenza infection in adults

Please cite this paper as: Fujimoto et al. (2012) Induction and maintenance of anti‐influenza antigen‐specific nasal secretory IgA levels and serum IgG levels after influenza infection in adults. Influenza and Other Respiratory Viruses 6(6), 396–403. Objectives  To determine the induction and changes in anti‐influenza virus secretory IgA (s‐IgA) levels in nasal washes and serum IgG levels in patients with influenza. Methods  The study recruited 16 patients with influenza aged 35·6 ± 9·6 years in 2007/2008 and 2008/2009 seasons. Nasal washes and serum were obtained throughout the first year. Anti‐viral s‐IgA levels and neutralization activities in nasal washes, and serum anti‐viral IgG levels and hemagglutination inhibition (HI) titers were measured. Results  Anti‐viral(H1N1) s‐IgA to total IgA ratio and neutralizing antibody titer were low in nasal washes of all patients, whereas serum levels of anti‐viral IgG and HI titers varied widely at day 1·4 ± 1·0 postinfection. Both nasal s‐IgA and serum IgG levels later increased significantly, reaching peak levels at day 9·6 ± 3·3 postinfection. The induced nasal s‐IgA then returned toward the initial levels within 300 days, although the levels at day 143 ± 70 were 3·03‐fold of the initial. Individual serum IgG levels also returned toward the initial levels within 300 days, although the mean levels remained high probably because of re‐infection in a subgroup of patients. Although influenza A (H3N2) was a minor epidemic subtype in both flu seasons, a significant rise in nasal anti‐viral (H3N2) s‐IgA levels and a slightly increase in serum IgG levels were noted. Conclusion  Low levels of nasal anti‐viral s‐IgA and neutralizing antibody were noted compared with a wide range of serum anti‐viral IgG and HI titers at the onset of infection. Elevated s‐IgA and IgG returned toward the initial levels within 300 days of infection with minor exceptions.