Figure 1 shows that, in patients with periodontitis, homozygotes “CC” of IL-4 -590C/T polymorphism and “11” of IL-4 VNTR play an important role in the response of peripheral blood lymphocytes to stimulation with bacteria. T. forsythia is an important stimulator of production of cytokines TNFα, IL-6, IL-10, IFNγ, IL-10, and IL-1β while P. intermedia affects the in vitro production of IL-6 and IL-10 in patients with periodontitis. Production of IL-17, IL-4, and IL-5 was not affected by the short-term stimulation by any of the above factors (Figure 1). This evidence concerns the gene IL17A and periodontitis.