IL-18 together with anti-CD3 antibody induces human Th1 cells to produce Th1- and Th2-cytokines and IL-8.

Although IL-18 was initially regarded as a factor that enhances IFN-gamma production from Th1 cells, later studies revealed its potential to induce Th2 cytokine production from T cells, NK cells and basophils/mast cells. Very recently, we demonstrated that passively transferred memory phenotype Th1 cells induce airway inflammation and hyperresponsiveness in a host mouse by production of Th1-, Th2-cytokines, GM-CSF and chemokines, when the transferred cells are stimulated in the host mice with nasally administered Ag and IL-18. Moreover, IL-18 is suggested to contribute to asthma exacerbation in human patients. Therefore, it is important to determine whether human Th1 cells also have the potential to produce these soluble factors when stimulated with anti-CD3 and IL-18 in vitro. Here we demonstrated that only Th1 cells, but not Th2 cells, produce IFN-gamma, IL-13, GM-CSF and IL-8 after stimulation with anti-CD3 and IL-18. Furthermore, highly purified IFN-gamma-producing Th1 cells have the same potential. Thus, human Th1 cells may become very harmful cells, when stimulated with Ag and IL-18 in vivo, and produce IFN-gamma, IL-13, GM-CSF and IL-8, which in combination might induce severe inflammation such as airway inflammation.