CH5 - T cell mediated immunity Flashcards
Q -What are the components of the TCR complex? Which of these components are responsible for antigen recognition and which for signal transduction
The T cell receptor (TCR) complex is made up of the TCR α and β chains, which are responsible for antigen recognition, and the CD3 complex and ζ homodimers, which are required for signal transduction.
Q - What are some of the molecules in addition to the TCR that T cells use to initiate their responses to antigens, and what are the functions of
Molecules other than the TCR used by T cells to respond to antigens include the CD4 and CD8 coreceptors, which bind to class II and class I MHC molecules, respectively; costimulatory receptors such as CD28, which bind to costimulators expressed on activated antigen-presenting cells (APCs); and adhesion moelcules such as intergrin LFA-1, which mediate T cell adhesion to APCs and also control the migration of T cells
Q- What is costimulation? What is the physiologic significance of costimulation? What are some of the ligand-receptor pairs involved in costimulation
Costimulation refers to signals delivered to a lymphocyte that are required for lymphocyte activation in addition to but independent of antigen receptor signaling. Costimulatory signals are commonly referred to as a “second signal” (antigen being “signal 1”) and provide lymphocytes with the information that the antigen they are recognisizing may be microbial orgin. B7-1 (CD80) and B7-2 (CD86) are the makor constimulators on APCs, which bind to CD28 on T cells.
Q - Summarize the links among antigen recognition, the major biochemical signaling pathways in T cells, and the production of transcription factors
Antigen recognition results in coreceptors in T cells bringing the Lck tyrosine kinase bound to the cytosolic tail of CD4 or CD8 in proximity to CD3 and ζ chain ITAMs. Phosphorylation of the ITAMs by Lck results in the recruitment and activation of ZAP-70 tyrosine kinase, which in turn phosphorylates several other adaptor protein and enzymes, which initiates many different signaling pathways by activating different downstream enzymes. Some of these pathways include activation of phospholipase Cγ, resulting in calcium signaling and the subsequent activation of the NFAT transcription factor; activation
- activation of PKCΦ –> resulting in activation of NF-кB transcription factor;
Q- What is the principal growth factor for T cells? Why do antigen-specific T cells expand more than other (bystander) T cells on exposure
The major growth factor for T cells is interleukin-2 (IL-2). It is produced by T cells in response to antigen receptor signals and costimulation. T cells that have recognized antigens express increased levels of receptors for IL-2 and thus preferentially respong to growth factor during immune responses to the antigens.
Rrgulatory T cells (Tregs) also IL-2 for their survial and function
Q- What are the mechanisms by which CD4+ effector T cells activate other leukocytes?
CD4+ helper T cells activate other cells (B lymphocytes, macrophages) by the surface molecule CD40-ligand engaging CD40 on the other cells and by the actions of secreted cytokines
Q - What are the major properties of memory T lymphocytes?
Memory cells survive after the antigen is cleared and respond more rapidly and strongly to antigen exposure than do naive cells
Q- Why do naive T cells migrate preferentially to lymphoid organs and differentiated effector T cells (which have been activated by antigen) migrate preferentially to tissues that are
Naive T cells express the adhesion molecule L-selectin and the chemokine receptor CCR7, which mediate homing to lymph nodes. Differentiated effector cells lose expression of these molecules and instead express adhesion molecules that bind to molecules on endothelium exposed to inflammatory
