Youngsters’ over-reactive immune response ‘fatal during pandemic flu’

LONDON - A new study has claimed that in young adults, a strong immune response can overreact in a violent and uncontrolled fashion, resulting in fatalities.

Fernando Polack at Vanderbilt and colleagues in Argentina and Nashville suggest that people are made critically ill, or even killed, by their own immune response.

A molecule called C4d, a product of this biochemical cascade (the complement system), is a marker for the strength of immune response. In adults who died during the 2009 H1N1 pandemic, high levels of C4d in lung tissues suggest a massive, potentially fatal activation of the complement system.

“C4d is part of the inflammatory cascade, and while it’s really good at killing organisms and protecting us, it’s sort of the slash and burn approach, capable of causing lots of tissue damage,” said Joyce Johnson, professor of Pathology with VUMC.

As to why infants and the frail elderly escaped this mechanism of death in the H1N1 pandemic, Polack said, “We found in 2009, the elderly had good immunity because they had seen a very similar virus sometime before 1957. Babies hadn’t seen many viruses at all so there was no trigger. It came down to the young adults - primed with an ineffective response. Their bodies already had defenses against previous influenza viruses that look like this one but weren’t close enough.”

“It suggests this (immune over-reaction) is what happens with pandemic to make young healthy adults seriously ill. There are other things that contribute to threat, but this is one of the main things for this age group,” Polack said.

The study is published Dec. 5 in Nature Medicine. (ANI)