The role of oestrogen as the primary female sex hormone, regulating both the menstrual cycle and the menopause, has been understood for nearly a century. However, a new study published in the journal Proceedings of the National Academy of Sciences describes a novel role for the hormone in increasing the strength of the immune system to infections. Scientists at the McGill University Health Centre (MUHC) in Montreal and the Centre of Molecular Medicine and Therapeutics in Vancouver, Canada, and the Merck Research Laboratories, USA, collaborated in the study. The work supports a growing body of evidence that women have a stronger immune response than males.
The paper shows that in mice, the oestrogen directly blocks the gene coding for a protein called caspase-12. Normally, caspase-12 dampens down the 'inflammatory response', the body's first line of defence against infections.
The study is unique in that, whilst it like many others was carried out in genetically modified mice, it used human proteins to formulate its conclusions. Specifically, male and female mice were created that lacked a working caspase-12 gene. Without this gene, the animals have extremely effective immune responses. Then, human caspase-12 was inserted into these mice. Expecting the new gene to dampen down the immunity system, the researchers were surprised to see that only the males became less healthy when infected with a strain of bacteria. Females remained unaffected by human caspase-12, and stayed perfectly healthy when infected.
'We were very surprised by these results, and we determined that the oestrogen produced by the female mice blocked the expression of the human caspase-12 gene', explained Dr Maya Saleh, of MUHC and lead author on the paper. One key finding was that, by giving them a synthetic form of oestrogen, male mice too returned to their previously super-immune state.
Dr Leslie Knapp, of the University of Cambridge, UK, offered some explanation of the finding that females may have stronger immune systems than men. 'In evolutionary terms it only takes one male to reproduce with lots of females, but females are much more important in terms of producing offspring'.