Ghent, Belgium. New research focuses on the role of MicroRNAs encoded on the X chromosome to explain why women have stronger immune systems to men and are less likely to develop common illnesses and cancer.

The phrase man flu came into the use as a way of describing the seemingly exaggerated symptoms of males who have a cold, but claim a bad case of the flu. The term is pejorative, but there is growing scientific evidence to support the notion of a sex-linked difference in immunity.


The current research, led by Dr Claude Libert from Ghent University in Belgium, published in the journal BioEssays, seems to support the idea that women have stronger immune systems than men. "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 Libert.



Claude Libert, PhD, Department for Molecular Biomedical Research, Ghent University.Libert's team focused on MicroRNA, tiny strains of ribonucleic acid which alongside DNA and proteins, make up the three major macromolecules that are essential for all known forms of life. "We believe this is due to the X chromosome which in humans contains 10% of all microRNAs 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."

The scientists propose that the biological mechanisms of the X chromosome have a strong impact on an individual's genes, known as genetic imprinting, that provides immunological advantage to females. To develop their hypothesis, they produced a detailed map of all described microRNAs which have a role in immune functions and cancer in both human and mouse X chromosomes.

"We believe this immunological advantage is due to the silencing of X-linked genes by these microRNAs," said Libert. "Gene silencing and inactivation skewing are known mechanisms which affect X-linked genes and may influence X-linked microRNAs in the same way." This genetic silencing leaves males at an immunological disadvantage as a male has only one X-chromosome. The Y-Chomosone contains fewer genes so if the genes involved in immunity are silenced maternally the male is left with no compensating genetic information.

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

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