Do food allergies make MS worse?
American Academy of Neurology (AAN) annual meeting, Vancouver, B.C., April 15-21, 2016
Researchers have long speculated about the relationship – if any – between allergies and multiple sclerosis. Allergic conditions, such as asthma, hay fever and dermatitis, are characterized by one type of overactive immune response (involving Th2 immune cells), whereas a different immune response (involving Th1 cells) is present in MS. A Th2 response is beneficial in MS, so there was the suggestion that allergies might have a protective effect. Indeed, a population-based study in Italy suggested that people with allergic conditions (such as asthma) appeared to have a lower risk of developing MS (Pedotti and colleagues. Mult Scler 2009;15:899-906). In contrast, a review of 10 studies found no association between allergic conditions and MS (Monteiro and colleagues. Acta Neurol Scand 2011;123:1-7).
That said, the two immune response (Th1 and Th2) could coexist in the same person, which raises the question of whether allergies have an impact on a person’s MS. This issue was examined in the CLIMB study that is ongoing at Harvard University in Boston (Diaz-Cruz and colleagues. AAN 2016; abstract P2.187). The study involved over one thousand people with and without allergies to environmental triggers (e.g. pollen), foods or medications. The average age of participants was 50 years, and they had been living with MS for an average of 16 years. Overall, people with allergies had somewhat more active MS. This effect was significant only for those with food allergies. People with food allergies had a slightly higher rate of relapses, but there didn’t appear to be an impact on disability progression.
The culprit may be a component of the immune system called the mast cell, which has been attracting attention in recent years for its possible role in MS. Mast cells are perhaps best known for releasing histamine, which dilates blood vessels (the cause of stuffy noses) and for which people take remedies such as antihistamines. But mast cells have other roles that may be important to MS. They can activate T cells, which cause inflammation in MS; and they degrade the blood-brain barrier, which enables immune cells to enter the brain and cause the inflammatory lesions seen in MS.
As a result of these findings, a few studies have looked at whether antihistamines might be helpful in MS. A pilot study found that taking an antihistamine seemed to stabilize or improve neurological function in people with MS (Logothetis and colleagues. Int J Immunopathol Pharmacol 2005;18:771-778). In the UK, researchers found that allergies didn’t appear to affect the development of MS, but taking antihistamines did seem to lower the risk of MS (Alonso and colleagues. Neurology 2006;66:572-575). However, a database analysis subsequently reported that among people on Copaxone, taking an antihistamine didn’t appear to provide any additional benefit (Ollendorf and colleagues. J Neurosci Nurs 2008;40:281-290).
The importance of mast cells in MS remains unclear but is still being researched. One drug that specifically targets mast cells, called masitinib (AB1010), was shown to be beneficial in a pilot study of people with progressive MS (Vermersch and colleagues. BMC Neurol 2012;12:36). A larger trial is reportedly underway but no results have been reported yet.
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