Ethnicity could cause immunity to the H7N9 influenza virus to vary

Owing to genetic differences, people could vary in their ability to mount a cell-mediated immune response against the H7N9 influenza virus that emerged in February last year, a new study has suggested.

Animal and human studies suggest that, in the absence of protective antibodies against a new influenza strain, cross-reactive CD8+ T lymphocytes (CTLs) generated previously against other influenza strains can diminish disease severity, and may therefore provide some protection against the H7N9 virus.

Peter Doherty and colleagues investigated the capacity of pre-existing influenza-specific CTLs to respond to the H7N9 virus in individuals not previously exposed to the virus.

The researchers found that 28 per cent of the H7N9 peptides with the capacity to elicit CTL responses are also found in other influenza A viruses that caused past human pandemics or epidemics.

They then estimated that the human leukocyte antigens (HLAs) capable of presenting immunogenic influenza peptides to CTLs are present in approximately 16-57 per cent of the population, and vary in prevalence depending on ethnicity.

Analyses of blood cells from 52 healthy human donors incubated with the peptides in vitro revealed that some HLA alleles elicit robust CTL responses against any human influenza A virus, including H7N9, whereas other alleles, such as those that tend to be prevalent in the indigenous people of Alaska and Australia, displayed limited CTL responses.