'Man flu' - do women just have stronger immune systems?

Gene differences between men and women could mean that women are better at resisting certain infections and diseases than men, a new study suggests. The second X chromosome in women gives them an immunological advantage over men, possibly giving credence to man's perceived susceptibility to 'man-flu'. The authors of the study said the results could have important implications in the development of drugs and treatments for cancer.

'Statistics show that in humans, as with other mammals, females live longer than males and are more able to fight off shock episodes from sepsis, infection or trauma', said Dr Libert. 'We believe this is due to the X chromosome which in humans contains 10 percent of all micro RNAs [small fragments of RNA] detected so far in the genome. The roles of many remain unknown, but several X chromosome-located strands of microRNA have important functions in immunity and cancer'.

Women have two X chromosomes whereas men have one X and one Y chromosome. The X chromosome, larger and containing more genes than its Y counterpart, houses immunity genes which help in the fight against infections and cancer. However, the function of these genes can be blocked by a process known as gene silencing. Silencing the genes in one of a female's two X chromosomes compensates for the unequal gene expression between the sexes. But the study, led by Dr Claude Libert of Ghent University in Belgium, showed that some female genes can escape the silencing process, leaving women with up to twice as many disease fighting gene products than men. This may enable women to fight off certain illnesses more effectively than men.

'How this unique form of genetic inheritance influences X chromosome linked microRNAs will be a challenge for researchers for years to come, not only from an evolutionary point of view, but also for scientists investigating the causes and cures of disease', Dr Libert said.

However, it is not all good news for women. The study also notes that the advantages in having two X chromosomes are slightly offset by the fact that it increases 'their susceptibility to develop autoimmune disorders later in life', the study authors wrote.