Your sense of smell might be more important than you think. It could indicate how well your immune system is functioning, a study in mice suggests.

Evidence of a connection between the immune system and the olfactory system – used for sense of smell – has been building for some time. For instance, women seem to prefer the scent of men with different immune system genes to their own. Meanwhile, other studies have hinted that the robustness of your immune system may influence how extraverted you are.

To investigate further, Fulvio D’Acquisto at Queen Mary University of London and his colleagues studied mice missing a recombinant activating gene (RAG), which controls the development of immune cells. Without it, mice lack a working immune system and some genes are expressed differently, including those involved in the olfactory system. “That rang bells, because people with immune deficiencies often lose their sense of smell,” says D’Acquisto. Systemic lupus erythematosus, an autoimmune disease in which the immune system mistakenly attacks tissues in the skin, joints, kidneys, brain, and other organs, is one such example.


His team measured how long it took mice to find chocolate chip cookies buried in their cages. Those missing RAG took five times as long as normal mice. They also failed to respond to the scent of almond or banana, which mice usually find very appealing – although they did still react to the scent of other mice.

Further study uncovered abnormalities in the lining of their noses; physical evidence that their sense of smell might be disrupted.

D’Acquisto suspects olfactory cell survival might hinge on the presence of some factor released by immune cells. There could be an evolutionary benefit: “If you have a problem with the immune system, it would be a good idea to avoid exposing yourself to danger,” D’Acquisto says. “Not smelling properly could encourage you to stay still.”

There could also be an indirect link, says Daniel Davis, an immunologist at the University of Manchester, UK, and author of The Compatibility Gene. “Maybe both are influenced by the microbiome, for example, which will be altered in the mice with a genetic alteration to their immune system,” Davis says.

He also points out that it is hard to know how much impact this lab-based measurement of smell would have on the actual behaviour of a wild animal. “Overall, however, this paper adds to several other studies linking smell with other body systems, including the immune system,” he says.

D’Acquisto suspects that different types of immune deficiency may have a variety of effects on sense of smell and behaviour. Someday, he says, it might even be possible to diagnose certain illnesses based on these alterations in smelling ability.

Journal reference: Frontiers in Neuroscience, DOI: 10.3389/fnins.2015.00318

(Image: Sally Anscombe/Getty)