They were also more likely to develop a severe form of a disease associated with multiple sclerosis in humans.
The scientists then conducted a closer examination of these effects at a molecular level.
Laboratory tests revealed that salt exposure increased the levels of cytokines released by Th17 cells 10 times more than usual. Cytokines are proteins used to pass messages between cells.
Study co-author Ralf Linker, from the University of Erlangen-Nuremberg, said: ‘These findings are an important contribution to the understanding of multiple sclerosis and may offer new targets for a better treatment of the disease, for which at present there is no cure.’
It develops when the immune system mistakes the myelin that surrounds the nerve fibres in the brain and spinal cord for a foreign body.
It strips the myelin off the nerves fibres, which disrupts messages passed between the brain and body causing problems with speech, vision and balance.
Another of the study’s authors, Professor David Hafler, from Yale University, said that nature had clearly not intended for the immune system to attack its host body, so he expected that an external factor was playing a part.
He said: ‘These are not diseases of bad genes alone or diseases caused by the environment, but diseases of a bad interaction between genes and the environment.
‘Humans were genetically selected for conditions in sub-Saharan Africa, where there was no salt. It’s one of the reasons that having a particular gene may make African Americans much more sensitive to salt.
‘Today, Western diets all have high salt content and that has led to increase in hypertension and perhaps autoimmune disease as well.’
The team next plan to study the role that Th17 cells play in autoimmune conditions that affect the skin.
‘It would be interesting to find out if patients with psoriasis can alleviate their symptoms by reducing their salt intake,’ they said.
‘However, the development of autoimmune diseases is a very complex process which depends on many genetic and environmental factors.’