Over-Reactive Immune System Kills Young Adults During Pandemic Flu

[Elmore Furth]

The mystery of why healthy young adults die from influenza is now starting to be answered.

ScienceDaily (Dec. 5, 2010) — A hallmark of pandemic flu throughout history, including the 2009 H1N1 pandemic, has been its ability to make healthy young and middle-aged adults seriously ill and even kill this population in disproportionate numbers. In a paper published Dec. 5 in Nature Medicine, Vanderbilt University Medical Center researchers provide a possible explanation for this alarming phenomenon of pandemic flu. The study's findings suggest people are made critically ill, or even killed, by their own immune response.

"Every time there is an influenza pandemic there is a large proportion of younger, or middle-aged adults who die. We have always explained these deaths, based on presumed virulence of virus, or getting bacterial infection at the same time. We now have vaccines and antibiotics, but still we see middle-aged individuals who die," Polack said.

"We have seen this before. Where non-protective antibody responses are associated with an immune-based disease in the lung," Polack said.

Polack has previously published evidence that a first-line immune response, primed by an imperfect antibody, can overreact in a violent and uncontrolled fashion. Patients die from lung damage inflicted by their own immune system. A molecule called C4d, a product of this biochemical cascade (the complement system), is a marker for the strength of the 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.

Pediatric infectious diseases expert, John Williams, M.D., assistant professor of Pediatrics, Microbiology & Immunology, and his lab found the signature for an influenza infection in 4 of the 53-year-old samples, and were able to confirm the lung tissues had high levels of C4d. These patients too had died from an over-reactive immune response.

"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," Johnson said.

But why did infants and the frail elderly escape this mechanism of death in the H1N1 pandemic?

"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," Polack said.




Over-Reactive Immune System Kills Young Adults During Pandemic Flu

[endless october]

1. Cytokine storm.

http://en.wikipedia.org/wiki/Cytokine_storm

[KT2000]

2. The 1918 Flu Epidemic

left many orphans because it was the young healthy adults who died from the same thing. Very sad.