Effector pathways regulating T cell activation.

Activation of T lymphocytes is a key event for an efficient response of the immune system. It requires the involvement of the T cell receptor antigen as well as costimulatory molecules such as CD28. Engagement of these receptors through the interaction with a foreign antigen associated with major histocompatibility complex molecules and CD28 counter-receptors B7.1/B7.2, respectively, results in a series of signaling cascades acting in synergy and which culminate in activation of interleukin-2 gene transcription and eventually cell proliferation. Many studies aimed at characterizing these specific effector pathways have been published; however, the actual signaling molecules that transduce activation signals from the cell membrane to the nucleus and that directly regulate interleukin-2 gene transcription are not yet completely defined and remain a matter of debate. In this commentary, we have attempted to analyze the results, which are sometimes diverging if not totally contradictory, characterizing effector pathways that possibly are triggered during T cell activation.