CHAPTER 5 T Cell-Mediated Immunity and Activation

Vocabulary flashcards covering T cell activation, differentiation, subsets, signaling pathways, and migration mechanisms based on the lecture material.

Helper T cells

Effector CD4 T cells that combat intracellular microbes by enhancing the killing functions of phagocytes through cytokines and the expression of CD40-ligand (CD40L).

Cytotoxic CD8 T cells (CTLs)

Cells of the adaptive immune system that combat viruses, Rickettsiae, and protozoa by killing the infected cells in which these microbes reside.

CD4 Th1 cells

A subset of CD4 cells that activate macrophages for enhanced phagocytosis and killing of microbes while augmenting inflammation.

CD4 Th2 cells

Cells that induce the switch of production of IgE antibodies to activate effector responses against extracellular parasites like helminth worms.

CD4 Th17 cells

Subset of CD4 cells that help recruit neutrophils to sites of infection early in the adaptive immune response against extracellular pathogens.

Tfh cells (Follicular helper T cells)

CD4+ T cells that remain in the lymph node follicles to stimulate B cells for antibody production and class switching.

Regulatory T cells (Treg)

A distinct population of CD4+ T cells that suppress adaptive immune responses to prevent autoimmunity and uncontrolled reactions.

Signal 1

The first signal for T cell activation involving the recognition of a peptide:MHC complex on an APC by a T cell receptor (TCR).

Signal 2

A costimulatory signal provided by the binding of molecules like B7-1 (CD80) or B7-2 (CD86) on an APC to receptors like CD28 on a T cell.

Signal 3

Signals commonly provided by cytokines in the microenvironment that drive the differentiation of CD4 T cells into specific subsets (Th1, Th2, Th17, Tfh, or Treg).

IL-2 (Interleukin-2)

A cytokine secreted by activated T cells that acts in an autocrine fashion to induce blastogenesis and clonal expansion.

LFA-1 (Leukocyte function-associated antigen 1)

An integrin on T cells that, upon TCR signaling, undergoes a conformational change to increase its affinity for ICAM-1 on APCs.

ICOS (Inducible co-stimulator)

A CD28-related protein expressed on T cells in germinal centers that is important for helper T cell function in B cell responses.

CTLA-4 (CD152)

An inhibitory receptor structurally related to CD28 that binds B7 molecules with higher avidity to inhibit T cell activation.

PD-1 (Programmed cell death 1)

An inhibitory receptor that recognizes ligands PD-L1 and PD-L2 to activate the phosphatase SHP2, inhibiting signals from CD28 and the TCR complex.

Checkpoint Blockade

A form of cancer immunotherapy that uses antibodies to block inhibitory receptors like CTLA-4 and PD-1 to treat cancer patients.

Adjuvant

Vaccine ingredients that mimic danger signals (PAMPs), recruit APCs, or create a slow-release depot effect to boost and prolong the immune response.

TCR Complex

A complex composed of the antigen-binding TCR$\alpha\beta$ heterodimer associated with four CD3 signaling chains (two $\epsilon$, one $\delta$, and one $\gamma$) and $\zeta$ chains.

ITAMs (Immunoreceptor tyrosine-based activation motifs)

Motifs on CD3 and $\zeta$ chains that are phosphorylated by Lck when TCRs and co-receptors (CD4 or CD8) bind peptide:MHC complexes.

Superantigens

Bacterial or viral toxins that stimulate a polyclonal activation of T cells by simultaneously binding class II MHC and specific V$\beta$ domains of TCRs.

CD25

The IL-2R $\alpha$ chain which, when combined with $\beta$ and $\gamma$ chains, forms the high-affinity receptor for IL-2 on activated T cells.

Immunological Synapse

The region of contact between an APC and a T cell where signaling molecules like the TCR and CD28 coalesce in the center while integrins form a peripheral ring.

Central Memory Cells

A subset of memory T cells that populate lymphoid organs and provide rapid clonal expansion upon re-exposure to an antigen.

Effector Memory Cells

Memory T cells found in mucosal and peripheral tissues that mediate rapid effector functions on reintroduction of antigens at those sites.

Tissue-resident Memory Cells

Memory T cells that occupy skin and mucosal tissues without recirculating to provide a first response against infections at body surfaces.

Sphingosine 1-phosphate (S1P)

A phospholipid higher in blood and lymph than in lymph nodes; its gradient draws T cells out of the lymph node into circulation.

Diapedesis

The process by which a lymphocyte squeezes between two endothelial cells to leave the blood and enter the lymph node.

Apoptosis

Programmed cell death that eliminates many effector T cells within 1–2 weeks after an infection is eradicated to return the system to homeostasis.