T cells and lymphokines.

T lymphocytes are one of the richest sources of protein mediators. Many of their effects, such as T cell help, growth stimulation, macrophage activation or suppression are caused by the release of these molecular mediators, which include the interleukins IL-2, IL-3, IL-4, IL-5, IL-6, interferons alpha and beta (IFN alpha and beta), tumour necrosis factor (TNF), lymphotoxin (LT), granulocyte macrophage colony stimulating factor (GM-CSF) and transforming growth factor beta (TGF beta). These molecules are only produced transiently after activation of the cells, and the CD4 (cluster differentiation antigen 4) cells are the richest sources of cytokines