Determination of serum antibodies against swine-origin influenza A virus H1N1/09 by immunofluorescence, haemagglutination inhibition, and by neutralization tests: how is the prevalence rate of protecting antibodies in humans?

Abstract

In April 2009, a new variant of influenza A virus, subtype H1N1v emerged in Mexico and spread all over the world producing the H1N1 pandemic in mankind after 1918-1920 and 1978/1979. Obviously there was no herd immunity against this new virus variant. Mainly young people, but less elderly were affected and presented severe and even lethal courses of disease. Since virus-specific antibodies are commonly regarded as markers of partial or complete immunoprotection, we performed antibody determinations in serum samples obtained from people before and after the pandemic has arrived in our region (Frankfurt/M., Germany). The assays were done by indirect immunofluorescence, by neutralization test, and by a haemagglutination inhibition test (HI), which was established in a practical modification for general and easy use. Among 145 individuals, of whom serum specimens had been drawn before the onset of pandemic, 19 revealed humoral immunity, i.e. titres of H1N1v neutralizing antibodies (at least 1:64). Eleven were older than 60 years, one belonged to the age group 40-59 years, three to the age group 20-39 years, and two to the age group 15-19 years. After the onset of pandemic in Frankfurt, serum specimens drawn from n = 225 randomly selected patients of our local university hospital were investigated for antibodies against H1N1v by HI, which is generally recommended for routine check of immunity. Twenty-eight individuals revealed the protecting antibody titre of at least 1:40. The age distribution had moved to mean age groups. The results fit to the incidence of influenza A/H1N1(09) disease, as confirmed by RT-PCR in patients admitted to our hospital, peaking in the younger age groups up to 30 years (second affected group: 30-40 years). While commonly used solid-phase antibody tests (like immunofluorescence) are not suitable to diagnose passed H1N1(09) infection and acquired immunity, this can be easily done by HI. Expecting the next waves of influenza A/H1N1v infections, HI testing may avoid vaccinations under special risk of severe or hidden adverse reactions.

Vaccination against pandemic H1N1 (2009) in patients after allogeneic hematopoietic stem cell transplantation: a retrospective analysis

“…Antibody titers were measured by a HI assay as previously described [19]. Serum samples were pretreated with receptor-destroying enzyme for inactivation of non-specific inhibitors.…”

Serological response to influenza A H1N1 vaccine (Pandemrix®) and seasonal influenza vaccine 2009/2010 in renal transplant recipients and in hemodialysis patients

“…Geometrical mean of the respective HI titer was calculated for each proband. Seroprotection was deWned as a hemagglutination inhibition antibody titer of ¸1:40, representing a 50% protective threshold [21,22].…”

Comparison of pro-inflammatory cytokine expression and cellular signal transduction in human macrophages infected with different influenza A viruses

“…Influenza A viruses cause seasonal influenza epidemics (associated with high seroprevalences in the affected populations and significant over-mortality) and represent a permanent threat of deleterious pandemics [1][2][3][4][5][6]. Currently, circulating seasonal influenza A viruses are H1N1 and H3N2 viruses.…”