Figure 3 Hypothetical mechanisms of smoking-associated processes that contribute to risk of multiple sclerosis Figure 3 | Hypothetical mechanisms of smoking-associated processes that contribute to risk of multiple sclerosis. Smoking promotes activation of proinflammatory pathways, and alters post-translational modification of peptides. Both events can lead to activation of resident CD4+ CNS-antigen-specific autoimmune T cells through recognition peptides presented by HLA-DRB1*15:01 molecules, a hypothesis supported by the fact that smoking increases the risk of rheumatoid arthritis in conjunction with HLA-DRB1*04. The less well understood protective role of class I HLA-A*02 might involve CD8+ cells. Olsson, T. et al. (2016) Interactions between genetic, lifestyle and environmental risk factors for multiple sclerosis Nat. Rev. Neurol. doi:10.1038/nrneurol.2016.187