The mechanism linking both smoking and exposure to organic solvents to multiple sclerosis (MS) risk may involve lung inflammation with a proinflammatory profile, according to a recent study. Their interaction with MS risk HLA genes argues for an action of these environmental factors on adaptive immunity, perhaps through activation of autoaggressive cells resident in the lungs subsequently attacking the central nervous system. Using a population-based case-control study (2,042 incident cases of MS and 2,947 controls), participants with different genotypes, smoking habits, and exposures to organic solvents were compared regarding occurrence of MS, by calculating odds ratios with 95% confidence intervals using logistic regression. Researchers found:

• Overall, exposure to organic solvents increased the risk of MS (odds ratio 1.5).
• Among both ever and never smokers, an interaction between organic solvents, carriage of HLA-DRB1*15, and absence of HLA-A*02 was observed with regard to MS risk, similar to the previously reported gene-environment interaction involving the same MS risk HLA genes and smoke exposure.