Interestingly, a single-nucleotide polymorphism (SNP) in the IL-4 receptor (IL-4R), which decreases the strength of IL-4 signaling, results in higher serum IL-17 levels and Th17 cells in RA patients vs. healthy individuals [164], suggesting that this specific IL-4R allele may allow unrestricted IL-17-mediated inflammation. Here, IL17A is linked to rheumatoid arthritis.