Transcript Chapter 8
Activation of T Lymphocytes
Activation and effector phases of T cell-mediated adaptive immune responses
are triggered by antigen recognition by T lymphocytes
Naive T lymphocytes home to secondary lymphoid organs, where they may
encounter antigens presented by mature dendritic cells on class I or class II
MHC molecules and thus become activated
Antigen-stimulated T cells that have received both "signal one" through the
antigen receptor and "second signals" via co-stimulatory receptors may be
induced to secrete cytokines and to express cytokine receptors (like IL-2)
T cell responses decline after the antigen is eliminated by effector cells
The proliferation of T lymphocytes and their differentiation into effector and
memory cells require antigen recognition, costimulation, and cytokines
Antigen is always the necessary first signal for the activation of lymphocytes,
ensuring that the resultant immune response is specific for the antigen
Activation of naive T cells requires recognition of antigen presented by
dendritic cells
Elimination of antigen leads to contraction of the T cell response, and this
decline is responsible for maintaining homeostasis in the immune system
Costimulation and growth factors like IL-2 stimulate expression of the antiapoptotic proteins Bcl-2 and Bcl-XL in the activated lymphocytes, and these
proteins keep cells viable
The inhibitory receptors CTLA-4 and PD-1, apoptosis induced by death
receptors of the TNF receptor superfamily (such as TNFRI and Fas), and
regulatory T cells