Immune System, Inflammation, Migraine - The Role of Cytokines and Regulatory T Lymphocytes in Migraine Pathophysiology

Migraine is the 6th most frequent disease (14% of the population) and the second leading cause of disability worldwide. From puberty and onward, migraine is 2 to 3 times more frequent in women, which also suffer from more severe attacks. Migraine is also up to twice as prevalent in patients suffering from autoimmune or inflammatory diseases such as multiple sclerosis (MS), rheumatoid arthritis (RA), Crohn disease (CD), systemic lupus erythematosus (SLE) and endometriosis, whereas patients with long standing type 1 diabetes mellitus (T1DM) - an autoimmune but non inflammatory disease - seem to be less affected compared to the general population.

Despite the identification of the role of peptides such as CGRP in migraine pathophysiology and the development of targetted anti-CGRP treatments, many patients remain unresponsive and the mechanisms behind migraine are still unclear.

The trigemino-vascular system is involved in the perception of migraine pain. Migraine occurs with trigemino-cervical neuron sensitization, leading to peptide secretion (such as CGRP, PACAP-38 and VIP), which induce neurogenic inflammation that is responsible for vasodilation, capillary leakage, oedema and further sensitization of the trigemino-vascular system, leading to amplified perception of migraine pain. CGRP, PACAP-38 and VIP infusions all induce migraine attacks in migraine patients, and only mild or no headache in healthy volunteers.

Sex hormones, prolactin and insulin are also involved in migraine pathophysiology, and the immune system, through cytokine production and immune cell dysregulations seems to also play a role in the pathogenesis of migraine. Both are closely related as sex hormone levels may have an influence on the levels of certain immune cell subtypes. Several pro-inflammatory cytokines (tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma and interleukin (IL)-6) were shown to be elevated in migraine patients but also inflammatory diseases such as MS and endometriosis compared to controls and are associated with migraine pathophysiology. Inflammation seems to be a common factor for migraine and these diseases. However, these studies provide conflicting results and further investigation is needed to better understand the role of inflammation in migraine pathophysiology.

Among T lymphocytes, regulatory T (Treg) cells regulate inflammation by suppressing effector T cells through several suppressive mechanisms such as IL-10 secretion or the hydrolysis of pro-inflammatory and nociceptive adenosine triphosphate (ATP) into anti-inflammatory and anti-nociceptive adenosine by cluster of differentiation (CD) 39 and 73 enzymes on the Treg cell surface. Recent studies have suggested decreased Treg proportions in migraine patients, particularly CD 39 and CD 73-positive Treg cells, whereas Treg cells were shown to be increased in T1DM patients. This suggests the role of Treg cells in migraine, but further studies are needed.