Evolution of the type-1 (Th1)-type-2 (Th2) cytokine paradigm.

During the past 12 years, since the discovery of murine Th1 and Th2 clones, increasing numbers of cells that make type-1 and type-2 cytokines have been recognized, and a growing number of these cytokines have been described. Emphasis has shifted from the CD4+ T cell, as the source of Th1-Th2 cytokines, to the functional effect of the type-1 and type-2 cytokines, independent of their cell of origin. Appreciation of the complex interactions of CMI and humoral immune responses continues to evolve. If this new paradigm provides insight into infectious disease pathogenesis and prevention, then it should allow development of new vaccines and vaccine adjuvants against these diseases.