For instance, increased periodontal pathogen abundance will enhance the stimulation of TLRs, induce Th1 to secrete IL-2, IFN-γ, TNF-α to kill intracellular infection pathogens, and then induce Th2 to secrete IL-4, IL-5, IL-6, IL-13 to regulate humoral immunity and limit Th1 response (51). The gene discussed is IL4; the disease is infection.