Flu attacks immune memory cells

Scientists at the Whitehead Institute in the US have made a step forward in understanding why the flu virus is so deadly. And they've done it in a very clever way.

When we're infected by the influenza virus, our immune system generates cells, known as B cells, that produce antibodies - special proteins that recognise the virus and neutralise it. A subset of these cells take up residence in the lungs, to help fight off the chances of reinfection by the virus through inhaling it.

These cells, known as memory B cells, are particularly good at recognising the virus, so they can spring into action and make more antibodies at the first sign of infection. But the scientists discovered that the flu virus infects and kills these cells in the lungs, making it harder to fight off the infection.

Unfortunately, it's very difficult to purify flu-infected B cells, so they had to take a more roundabout approach, using cloning techniques. They took the DNA - the nucleus - from a mouse B cell that could specifically recognise the flu virus, and put it into a mouse egg cell that had had its own DNA removed. This then created a mouse in which all the B cells can only recognise flu, so they could easily study the infection.

They discovered that the virus infected the flu-specific memory B cells in the lungs and killed them, while flu-specific B cells in another part of the body - the lymph nodes - weren't destroyed. So it looks like the flu virus specifically targets and kills the memory cells that are aiming to protect the body against reinfection from inhaled viruses, giving it another chance to gain a foothold before the rest of the immune system kicks in to tackle it.

The new results, published in Nature, help to explain why flu is so infectious, and could help with the design of vaccines, both for the annual flu shot or entirely new types of preventive approaches. And the techniques the lab have developed could be applied to studying how other viruses interact with cells in the immune system, which could bring health benefits in other diseases.