Immune cells are vital for our survival, but can turn nasty and attack healthy cellsKATERYNA KON/SCIENCE PHOTO LIBRARYAs women age, they produce an increasing number of killer immune cells, which hunt down and destroy infected cells. This discovery, and the fact that the same isnt true of men, could help to explain why women are less likely to catch infections but have higher rates of autoimmune conditions.We already know that women tend to have stronger immune systems than men, but because studies tend to focus on men or male animals, we lack a detailed understanding of