Generation of Human T Helper 1 and T Helper 2 Subsets from Peripheral Blood-Derived Naive CD4+ T Cells

CD4⁺ T helper (Th) cells are crucial for the generation of the antigen-specific immune response (1 ). They regulate many different aspects of the immune response, both by the secretion of cytokines and through cell surface expressed molecules. CD4⁺ precursor (Thp) Th cells or naive Th cells are fully developed Th cells that have left the thymic environment and have not yet encountered the specific antigen for their unique antigen-specific T-cell receptor (TCR). Thp cells have the capacity to differentiate into effector and memory Th cells with a wide variety of functional capabilities. The differentiation status of human resting Th cells can be distinguished by the cell surface expression of distinct isoforms of the molecule CD45 (1 ,2 ). Naive Th cells express high levels of the CD45RA form, in the absence of the CD45RO form, while previously activated Th cells (memory/effector Th cells) express high levels of the CD45RO form and low levels of the CD45RA form.