T-Cell Activation, Helper Subset Differentiation, and Memory

These flashcards cover T-cell activation, differentiation of helper subsets, and memory functionality in the immune response.

What is required for the activation of a naïve T cell?

Several receptor-ligand interactions, signals through cytokines, and interaction with a dendritic cell.

What does the two-signal hypothesis state in terms of T-cell activation?

Full T-cell activation requires three signals: Signal 1 (TCR engagement with antigen), Signal 2 (costimulatory signals), and Signal 3 (cytokines for differentiation).

What are the two parts of the immune synapse formed during T-cell activation?

Central supramolecular activating complex (cSMAC) and peripheral supramolecular activating complex (pSMAC).

What initiates the cascade of signaling in T-cell activation?

Binding of the TCR to the peptide-MHC complex.

What is T-cell anergy?

A state of nonresponsiveness in T cells caused by TCR engagement without costimulatory signals.

Which cytokine is crucial for T-cell proliferation after activation?

Interleukin-2 (IL-2).

How do CD28 and CTLA-4 function in T-cell activation?

CD28 promotes activation by amplifying TCR signaling, while CTLA-4 represses activation and limits proliferation.

What are the main functions of TH1 helper T cells?

Enhancing APC activity, promoting cytotoxic T cell activation, and protecting against intracellular pathogens.

How are CD4+ T helper cell subsets differentiated?

By polarizing cytokines that interact with T-cell receptors, leading to master gene regulators determining their fate.

What are the four broad subsets of memory T cells?

Stem cell memory T cells (TSCM), central memory T cells (TCM), effector memory T cells (TEM), and resident memory T cells (TRM).

What happens to most effector T cells after an immune response is resolved?

At least 90% undergo apoptosis, leaving a population of memory T cells.

What is the difference in activation requirements between naïve T cells and memory T cells?

Memory T cells have less stringent activation requirements and can be activated by various APCs, not just dendritic cells.

What cytokines regulate the differentiation of TH2 cells?

TH2 cells are regulated by IL-4 and other cytokines released during allergic and parasitic responses.

What is the role of T follicular helper (TFH) cells?

TFH cells provide help to B cells, enhance germinal center formation, and drive affinity maturation.

What are the effects of IL-4 as a TH2 effector cytokine?

Induces eosinophil differentiation and activation, and promotes B-cell activation and class switching to IgE.

What defines the outcome of an immune response related to T helper cell subsets?

The balance of activity among TH1, TH2, and other T cell subsets influences the type of immune response.

What factors influence the durability and function of memory T cells?

The self-renewing potential and life span of memory T cells decrease as they differentiate from TSCM to TEM.