IL-5 can be produced by e.g., Th2 cells, and there are indications that Th2-produced IL-5 is able to promote and expand antigen-specific Tregs that have been activated by IL-4 and autoantigens and that are involved in the suppression of autoimmunity, suggesting a beneficial effect of radon treatment in autoimmune diseases such as RA [44]. This evidence concerns the gene IL4 and rheumatoid arthritis.