T cells: Development, Activation, and Immunity Flashcards
T-cell development:
T cells develop in the thymus from hematopoietic stem cells, undergoing positive and negative selection to become functional.
Thymus selection process:
T cells undergo positive selection (survival if they can bind MHC molecules) and negative selection (elimination if they bind self-antigens too strongly).
Positive selection:
T cells that can recognize self-MHC molecules on thymic epithelial cells are selected for survival.
Negative selection:
T cells that bind self-antigens with high affinity are eliminated to prevent autoimmunity.
T-cell receptor (TCR):
A receptor on T cells that recognizes specific antigens presented by MHC molecules on other cells.
CD4+ T cells:
Helper T cells that recognize antigens presented on MHC Class II molecules and assist other immune cells.
CD8+ T cells:
Cytotoxic T cells that recognize antigens presented on MHC Class I molecules and kill infected or cancerous cells.
Naïve T cells:
Mature T cells that have not yet encountered their specific antigen.
T-cell activation:
Occurs when a T cell’s TCR binds an antigen-MHC complex on an APC, followed by co-stimulatory signals for full activation.
Co-stimulation:
Additional signals required for T-cell activation, often provided by B7-CD28 interaction between APCs and T cells.
Effector T cells:
Activated T cells that carry out immune functions, including cytotoxic killing or cytokine secretion.
Memory T cells:
Long-lived T cells that provide rapid protection upon re-exposure to the same antigen.
Clonal expansion:
The proliferation of activated T cells to produce many copies of themselves to fight the pathogen.
Helper T cell functions:
Secrete cytokines that activate B cells, cytotoxic T cells, and other immune cells, coordinating the immune response.
Cytotoxic T cell functions:
Kill infected or cancerous cells by inducing apoptosis through mechanisms like perforin and granzymes.
Treg (regulatory T cells):
Suppress immune responses to maintain self-tolerance and prevent autoimmunity.
T-cell immune response:
T cells help mediate the immune response by recognizing and responding to infected cells, cancer cells, and foreign antigens.
Activation of CD8+ T cells:
Requires antigen presentation on MHC Class I molecules and co-stimulatory signals, resulting in cytotoxic activity.
Activation of CD4+ T cells:
Requires antigen presentation on MHC Class II molecules and co-stimulatory signals, leading to helper functions.
Th1 cells:
A subset of CD4+ T cells that help fight intracellular pathogens, such as viruses, by activating macrophages and cytotoxic T cells.
Th2 cells:
A subset of CD4+ T cells that help fight extracellular pathogens by promoting B cell activation and antibody production.
Th17 cells:
A subset of CD4+ T cells involved in inflammation and defense against fungal infections.
Tfh cells (follicular helper T cells):
A subset of CD4+ T cells that assist in B cell activation and antibody production in lymphoid follicles.
T-cell differentiation:
The process by which T cells specialize into different subsets (e.g., Th1, Th2, Th17, Treg) based on cytokine signals.
Cross-presentation:
Dendritic cells can present exogenous antigens on MHC Class I molecules, activating CD8+ T cells.
T-cell memory formation:
Some activated T cells differentiate into memory T cells, which persist long-term and provide faster responses on re-exposure.
Immune synapse:
The interface between an antigen-presenting cell and a T cell where TCRs and co-receptors engage with MHC-antigen complexes.
T-cell exhaustion:
A state of dysfunction in T cells after prolonged activation, often seen in chronic infections or cancer.
MHC restriction:
T cells can only recognize antigens when they are presented by MHC molecules, a phenomenon called MHC restriction.
T-cell tolerance:
The process by which T cells learn to distinguish between self and non-self to avoid autoimmune responses.
T-cell apoptosis:
Programmed cell death of T cells that occurs after they have performed their function or if they are autoreactive.
Immune surveillance by T cells:
T cells monitor tissues for abnormal cells (e.g., infected or cancerous) and respond to threats.
Memory T cell function:
Memory T cells respond more rapidly and effectively to subsequent exposures to the same antigen.
