Background: Although ferret antisera used in influenza surveillance did not detect antigenic drift of A(H1N1)pdm09 viruses during 2015-16 season, low vaccine effectiveness was reported in adults. We investigated the immune basis of low responses to circulating A(H1N1)pdm09 viruses following vaccination. Methods: Over 300 paired adult (18-49 yrs) pre and post-vaccination sera collected in 6 seasons (2010-11 to 2015-16) were analyzed by hemagglutination inhibition assays to evaluate the antibody responses to thirteen A(H1N1) viruses circulated from 1977 to 2016. Microneutralization and serum adsorption assays were used to verify 163K- and 223R-specificity of antibodies. Results: Individual antibody profiles to A(H1N1) viruses revealed three priming patterns: USSR/77-, TW/86- or NC/99-priming. Over 20% of adults had reduced titers to cell-propagated circulating 6B.1 and 6B.2 A(H1N1)pdm09 viruses compared to the A/California/07/2009 vaccine virus X-179A. Significantly reduced antibody reactivity to circulating viruses bearing K163Q was only observed in USSR/77-primed cohort, whereas significantly lower reactivity caused by egg-adapted Q223R change was detected across all 3 cohorts. Conclusion: Both 163K-specificity driven by immune priming and 223R-specificity from egg-adapted changes in the vaccine contributed to low responses to circulating A(H1N1)pdm09 viruses following vaccination. Our study highlights the need to incorporate human serology in influenza surveillance and vaccine strain selection.

Here we define the epitopes on HA that are targeted by a group of 9 recombinant monoclonal antibodies (rmAbs) isolated from memory B cells of mice, immunized by infection with A(H1N1)pdm09 virus followed by a seasonal TIV boost. These rmAbs were all reactive against the HA1 region of HA, but display 7 distinct binding footprints, targeting each of the 4 known antigenic sites. Although the rmAbs were not broadly cross-reactive, a group showed subtype-specific cross-reactivity with the HA of A/South Carolina/1/18. Screening these rmAbs with a panel of human A(H1N1)pdm09 virus isolates indicated that naturally-occurring changes in HA could reduce rmAb binding, HI activity, and/or virus neutralization activity by rmAb, without showing changes in recognition by polyclonal antiserum. In some instances, virus neutralization was lost while both ELISA binding and HI activity were retained, demonstrating a discordance between the two serological assays traditionally used to detect antigenic drift.

Respiratory syncytial virus (RSV) is the most common cause of serious lower respiratory illness in infants and young children worldwide, making it a high priority for development of strategies for prevention and treatment. RSV can cause repeat infections throughout life, with serious complications in elderly and immunocompromised patients. Previous studies indicate that the RSV G protein binds through a CX3C chemokine motif to the host chemokine receptor, CX3CR1, and modulates the inflammatory immune response. In the current study, we examined the contribution of CX3CR1 to the immune response to RSV infection in mice. CX3CR1-deficient mice showed an impaired innate immune response to RSV infection, characterized by substantially decreased NK1.1(+) natural killer, CD11b(+), and RB6-8C5(+) polymorphonuclear cell trafficking to the lung and reduced IFNgamma production compared with those in wildtype control mice. Leukocytes from CX3CR1-deficient mice were poorly chemotactic toward RSV G protein and CX3CL1. These results substantiate the importance of the RSV G CX3C-CX3CR1 interaction in the innate immune response to RSV infection.

Human coronaviruses are one of the main causes of upper respiratory tract infections in humans. While more often responsible for mild illness, they have been associated with illnesses that require hospitalization. In this study, an assay for one of the human coronaviruses, OC43, was developed using a truncated recombinant nucleocapsid (N) protein antigen in an enzyme immunosorbent assay (ELISA) and evaluated using serum collected from HCoV-OC43-infected patients, healthy adults, and patients with other respiratory virus infections. Results showed that the diagnostic sensitivity and specificity of the assay were 90.9% (10/11) and 82.9% (39/47), respectively. To evaluate the clinical utility of the ELISA, serum samples collected from patients during an outbreak of HCoV-OC43 infection and previously identified as positive by HCoV-OC43 whole N ELISA were screened resulting in 100% diagnosis agreement between the testing methods. These results suggest that this assay offers a reliable method to detect HCoV-OC43 infection and may be a useful tool in coronavirus seroepidemiological studies.