The majority of T helper cells are naïve cells without specified patterns of cytokine production (Th0 cells). Upon stimulation by antigen-presenting cells, such as macrophages and dendritic cells (DC), they receive the signal via their ɑ/β T cell receptor (TCR) and differentiate into either T helper 1 (Th1) or T helper 2 (Th2) cells. DC are specialized cells for uptake, transport, processing and presentation of antigens to T cells (Mellman and Steinman 2001), and subsets of DC have been identified that may influence Th1 and Th2 development (Moser and Murphy 2000). They facilitate Th1 differentiation when they are stimulated via toll-like receptors (TLRs), by secreting IL-12, while.
