The greatest effect of stimulation with T. forsythia on production of IL-10 was observed in patients with periodontitis carrying the genotypes CC (-590C/T) and 11 (VNTR) of the gene encoding IL-4 while the increase in the levels of IFNγ, IL-1 β, IL-6, and TNFα in patients with the same genotypes was lower (P < 0.05). This evidence concerns the gene IL4 and periodontitis.