It is a common belief that working out regularly will not only keep us fit, but also strengthen our immune system. However, it also turns out that after running a marathon it is easier to catch a cold. What brings about this contradiction? Thanks to Tsinghua researchers, we may have found one piece to this puzzle.

In a recent study, carried out by Professor Qi Hai and Professor Zhong Yi from Tsinghua’s School of Medicine, in collaboration with Professor Hu Ji from ShanghaiTech University, a specific brain-spleen neural connection has been identified. The activity of this autonomic nerve pathway could enhance antibody responses, and the brain region that generates such activity can therefore control adaptive immunity. Because the activity comes from the relevant brain regions responding to bodily behaviors, their study suggests the possibility to enhance immunocompetency by behavioral intervention.

These researchers developed a surgical denervation protocol in mice, to break the connection between the brain and the spleen and found that antibody responses to immunization were reduced. Neurons in the central nucleus of the amygdala (CeA) and the paraventricular nucleus (PVN) that express the corticotropin-releasing hormone (CRH) were found to connect to and control the splenic nerve. Researchers used sophisticated tools to ablate, inhibit, or activate these neurons, and found that antibody responses could be correspondingly inhibited or enhanced after immunization.

Behaviorally, when researchers let mice stand on an elevated platform, which is stressful to the animal, they found CeA and PVN CRH neurons were activated and antibody responses can be increased. Interestingly, however, the researchers also noted that other strongly stressful behaviors failed to enhance but actually suppressed antibody responses. The likely reason, as they pointed out, is because CRH neurons also enhance immunosuppressive glucocorticoid hormones. When this latter effect dominates, as often associated with strongly stressful conditions, immunity is hampered.

By extrapolation, this observation might explain the apparent contradiction that regular, mild exercise could lead to stronger immunity, whereas a marathon might make us temporarily more susceptible to a common cold.

Their study, titled “Brain Control of Humoral Immune Responses Amenable to Behavioral Modulation”, is published in Nature. For more information, go to “Read More” at the bottom of the post.

Confronted by today’s COVID-19 pandemic, perhaps one thing we should all do to shore up our immune system is a workout routine that is only “mildly stressful”.

Take care and stay safe!