Mucosal antibody responses are directed by viral burden in children with acute influenza infection

Activated CD4+ T cells and CD14hiCD16+ monocytes correlate with antibody response following influenza virus infection in humans

The failure to mount an antibody response following viral infection or seroconversion failure is a largely underappreciated and poorly understood phenomenon. Here, we identified immunologic markers associated with robust antibody responses after influenza virus infection in two independent human cohorts, SHIVERS and FLU09, based in Auckland, New Zealand and Memphis, Tennessee, USA, respectively. In the SHIVERS cohort, seroconversion significantly associates with (1) hospitalization, (2) greater numbers of proliferating, activated CD4⁺ T cells, but not CD8⁺ T cells, in the periphery during the acute phase of illness, and (3) fewer inflammatory monocytes (CD14^hiCD16⁺) by convalescence. In the FLU09 cohort, fewer CD14^hiCD16⁺ monocytes during early illness in the nasal mucosa were also associated with the generation of influenza-specific mucosal immunoglobulin A (IgA) and IgG antibodies. Our study demonstrates that seroconversion failure after infection is a definable immunological phenomenon, associated with quantifiable cellular markers that can be used to improve diagnostics, vaccine efficacy, and epidemiologic efforts.

Post-infection seroconversion is associated with severity of influenza virus infection

Seroconverters have early proliferation and activation of CD4⁺ T cells

CD8⁺ T cells are unaffected

CD14^hiCD16⁺ monocytes in the blood and nasal mucosa is associated with antibody response

Serum and mucosal antibodies fail as prognostic markers during critical influenza A infection

BACKGROUND

Previous studies have indicated that the absence of serum antibodies to influenza A H1N1 virus on day 4 after onset of symptoms predicted a fatal outcome in patients critically ill with influenza. The underlying mechanism was suggested to be the trapping of anti-influenza antibodies in pulmonary immune complexes.

OBJECTIVES

To study serum and mucosal antibodies as prognostic markers in patients with severe influenza A H1N1 infection.

STUDY DESIGN

Blood and respiratory samples (n=324) from 12 patients with severe influenza were analysed for anti-H1N1 antibodies with and without immune complex dissociation from symptom onset until convalescence or death (follow up 14-169 days). Eleven healthy subjects were analysed for comparison.

RESULTS

One of the 12 patients died from influenza pneumonia and had no detectable anti-H1N1 serum antibodies. However, also 2 of the 11 surviving patients remained negative for anti-H1N1 serum antibodies during follow-up (20 and 41 days, respectively). In six of the 11 survivors serum antibodies on day 4 were negative, but turned positive between day 7 and 23. In the remaining 3 patients antibodies were detected in the first 4 days of illness. Mucosal IgG or IgA was detected in all of the patients regardless of their clinical outcome and in 4 of 11 healthy subjects. No mucosal immune complexes were found in the patient who died but were detected in 3 of the 11 survivors.

CONCLUSIONS

This study suggests that no prognostic conclusions can be drawn from anti-H1N1 serum and mucosal antibodies in patients with severe influenza.

Role of oxidative stress in infectious diseases. A review

Oxidative stress plays a dual role in infections. Free radicals protect against invading microorganisms, and they can also cause tissue damage during the resulting inflammation. In the process of infection, there is generation of reactive species by myeloperoxidase, NADPH oxidase, and nitric oxide synthase. On the other hand, reactive species can be generated among others, by cytochrome P450, some metals, and xanthine oxidase. Some pathologies arising during infection can be attributed to oxidative stress and generation of reactive species in infection can even have fatal consequences. This article reviews the basic pathways in which reactive species can accumulate during infectious diseases and discusses the related health consequences.