A Potential Pathway of Th2 Development during Primary Immune Response

Differential cytokine production (Thl versus Th2) by CD4+ T cells during an immune response plays an important role in determining the biological implications of the response. Th1 cells are characterized by the dominance of IFN-γ production while Th2 cells produce predominantly 1L-4. It is now well established that IL-12 is essential for the priming of Thl cytokine secreting T cells1 while IL-4 is critical in the priming of Th2 cytokine secreting T cells2. While it has been suggested that CD1 specific NK1.1 CD4+ T cells in the spleen3, or CD4- CD8-, TCRαβ+ T cells restricted by MHC class I4 might be the potential sources of IL-4 during primary immune responses, these have not been clearly demonstrated.