Effector Responses and Lymphocyte Activation

A set of vocabulary flashcards covering T cell and B cell effector responses, CD45 isoforms, CTL killing mechanisms, NK cell recognition, and antibody functions.

Cell-mediated immune response

An immune response effective against virus-infected cells, tumor cells, grafted tissues, fungi, intracellular parasites, and slow-growing intracellular bacteria like tuberculosis.

CD45RA

The isoform of CD45 containing exon 4 but lacking exons 5 and 6, which is expressed on naïve T cells.

CD45RO

The isoform of CD45 containing exons 3, 7, and 8, lacking the RA, RB, and RC exons; it is expressed on effector T cells and associates better with CD4/CD8 and the TCR complex.

Immunological synapse (IS)

A long-lasting cell conjugate formed in the T cell-APC contact zone essential for T-cell activation, where CD45 and Lck are initially recruited to the central supramolecular activation cluster (cSMAC).

IL-2 (Interleukin-2)

A cytokine secreted by activated helper T cells that stimulates cytotoxic T cells, B cells, and helper T cells.

Licensed APC

A dendritic cell that has interacted with an already-activated helper T cell through CD40 and B7, enabling it to activate cytotoxic T cells.

Perforin

A $65\,kDa$ protein released by CTLs that polymerizes in the presence of $Ca^{2+}$ to form cylindrical pores ($5-20\,nm$) in the target cell membrane.

Granzymes

Serine proteases released by CTLs that enter target cells through pores or vesicles to stimulate apoptosis and DNA fragmentation.

DiGeorge Syndrome

A condition where individuals are born without a thymus, resulting in a lack of T-cell mediated immunity and an inability to address intracellular infections.

CTL-Ps

Naïve cytotoxic T cells that require three signals for activation: antigen recognition on MHC I, costimulation (CD28-B7), and IL-2 interaction.

Fas-FasL interaction

A killing mechanism used by some CTLs and NKT cells where Fas ligand on the effector cell binds to Fas on the target cell to induce apoptosis.

Caspases

A family of more than 12 cysteine proteases that cleave aspartic acid and are activated during apoptosis to result in the orderly destruction of the target cell.

Missing self model

A model describing how NK cells recognize targets; NK cells kill cells that lack MHC class I molecules, which are often inhibited by viruses to evade CTL detection.

KIRs (Killer Cell Immunoglobulin-like Receptors)

Inhibitory receptors on NK cells that recognize specific MHC molecules and provide a negative signal to prevent killing.

NKT cells

Cells that bridge innate and adaptive immunity, possessing an invariant TCR that recognizes glycolipids presented by nonpolymorphic CD1d.

ADCC (Antibody Dependent Cell Mediated Cytotoxicity)

A process where cytotoxic cells like NK cells, macrophages, neutrophils, and eosinophils bind to the Fc portion of antibodies already bound to a target cell to trigger killing.

Plasma Cell

An antibody-secreting cell that is a descendant of an activated B lymphocyte.

Neutralization

A mechanism where antibodies combine with an antigen and block an active site, preventing the antigen from binding to receptors on tissue cells.

Agglutination

The process where divalent antibodies bind to more than one cell-bound antigen at a time, forming cross-linked clumps.

Precipitation

The clumping of soluble antigen molecules by antibodies, causing them to fall out of solution.