SYDNEY: When men get sick they often catch grief for embellishing their illness, but a new study using rodents has revealed a significant disparity in the way males and females fend off and recover from infections.
The study, published in the medical journal Blood, showed that the immune systems in female rodents included fundamental differences to their male counterparts, and could add some truth to the idea of ‘man flu’.
Females had a greater number of immune cells, faster immune response and fewer side effects from fighting off infection. These differences seemed to enable the females to recover much faster than the male rodents.
“We found that regardless of what we used to provoke the immune response, the result was always the same,” said Ramona Scotland, lead author and immunologist from the William Harvey Research Institute at Queen Mary, University of London.
“Compared to males, in females we see a reduction in overall immune cell activation. The net result always being milder symptoms with faster recovery.”
When an infectious disease enters the body, signals are produced that attract leukocytes, the white blood cells that defend against infections and foreign bodies. Two types of white blood cells involved in the defence are neutrophils and macrophages.
Neutrophils act somewhat like a double-edged sword, engaging the infection and killing it but also doing damage to the infected tissue. This damage contributes to the run-down feeling we experience when sick.
But what this new research shows is that the mechanism for females and males are significantly different. And it seems this difference is founded in how those other white blood cells, the macrophages, behave.
Testing the response
In the experiment, the researchers exposed both male and female rats and mice to different types of infections. They then observed the behaviour of the different sexes to see how they were affected.
They discovered that the male rodents were looking very sick within three hours, whereas the females behaved as if they hadn’t even been infected.
By controlling all the different variables of the experiment, Scotland knew that there was only one difference between the subjects. “Same genetics, same environment, same age, same amount of live bacteria, same day, same time. Different sex.”
Females more effective at fending off illness
In order to determine the cause of this difference in behaviour, the researchers measured the rodents’ immune responses by looking in their body cavity and lungs for the presence and number of white blood cells.
They found that the females had double the number of macrophages. In addition, these macrophages were shown to be able to ‘eat’ the invaders more effectively, while producing less of the signal that summons the neutrophils. This all added up to a set of female rodents that were much better equipped to fight off infection than males, and felt better while doing it.
Ken Shortman, an immunologist from the Walter and Eliza Hall Institute of Medical Research in Melbourne, agreed that the study was interesting.
“It provides a neat explanation for improved resistance to sepsis in females: enhanced macrophage reactivity and function so infection is combated, but coupled with improved T cell regulation to prevent it all getting out of hand,” he said.
Same story in humans?
However, he was cautious about suggesting a direct link between rodents and humans. “A balanced situation like that often varies between different mouse strains, let alone the bigger jump from rodents to humans. So obviously it will be essential to check if the same difference now applies between human males and females.”
Scotland says men looking for an excuse to get out of work shouldn’t use the findings. “But I do believe that there may well be situations that are labelled as ‘man flu’ where perhaps the man in question really is feeling extremely poorly and more so than their female partner who just fought off the same type of infection with greater ease.”