Basic Immunology and Immunomodulation

T lymphocytes constitute one of the two major classes of lymphocytes. These cells are derived from stem cells in hematopoietic tissues, undergo development and differentiation in the thymus, and then move to the peripheral lymphoid tissue. Peripheral T cells can be broadly divided into two groups based on their expression of the cell surface molecules CD4 and CD8. Functionally, Tcells are involved with the regulation of immune responses and have been implicated in "cellular immunity." In addition, the presence of T cells is necessary to allow B cells to develop into antibody-secreting cells.