Effector Responses

A comprehensive set of vocabulary flashcards covering cell-mediated effector responses, T-cell and B-cell activation, and cytotoxic mechanisms as described in the lecture.

Cell-mediated immune response targets

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

CD45RA

The CD45 isoform expressed on naïve T cells; it contains exon 4 but lacks exons 5 and 6.

CD45RO

The CD45 isoform expressed on effector T cells; it lacks RA, RB, and RC exons and associates better with the CD4/CD8 and TCR complex to dephosphorylate Lck and Fyn.

CD45

A large ($180-220\,kd$) transmembrane cell surface molecule expressed by all leukocytes with a cytoplasmic domain featuring tyrosine phosphatase activity.

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 recruited to the central supramolecular activation cluster (cSMAC).

Effector T cell adhesion molecules

CD2 and LFA-1, which are expressed $2-4$ fold higher on effector T cells than on naïve cells to adhere to LFA-3 and ICAMs on APCs.

Activated Helper T Cell (CD4+)

Cells that stimulate cytotoxic T cells (via IL-2), B cells (via IL-2, IL-4, IL-5, IL-6), macrophages, and other helper T cells.

Cytotoxic T Lymphocyte (CTL) activation signals

The three signals required are: 1. Recognition of antigen in a MHCI-peptide on a licensed APC, 2. Costimulatory signal (CD28-B7), and 3. IL-2 interaction with the IL-2 receptor.

Licensed APC

A dendritic cell that has interacted with an already-activated helper T cell through B7/CD40 and CD28/CD40 ligand, enabling it to activate cytotoxic T cells.

Perforin

A $65\,kd$ 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 the target cell (such as Granzyme B through the mannose-6-phosphate receptor) to initiate apoptosis.

Fas-FasL Interaction

A killing mechanism where FasL on the CTL binds to the Fas receptor on the target cell, leading to FADD activation and pro-caspase 8 activation to induce apoptosis.

Caspases

A family of more than $12$ cysteine proteases that cleave aspartic acid and are activated during apoptosis for the orderly destruction of a target cell.

DiGeorge Syndrome

A condition where an individual is born without a thymus, resulting in no T-cell mediated immunity, which makes them unable to effectively address intracellular infections.

Conjugate formation ("Kiss of death")

The first phase of CTL killing where LFA-1 on the CTL binds to ICAMs on the target cell, changing to high avidity if the antigen is recognized.

Natural Killer (NK) cells

Circulating lymphocytes ($5-10\%$) that lack specific antigen receptors (no TCR) and destroy infected or tumor cells, particularly those showing an absence of MHC class I.

Missing Self Model

The model explaining how NK cells recognize targets; they kill cells that lack inhibitory MHC class I ligands, which viruses often downregulate to evade CTLs.

NKG2D

A candidate C-type lectin activating receptor on NK cells.

KIRs (Killer-cell Immunoglobulin-like Receptors)

Receptors on NK cells that recognize specific MHC molecules to provide an inhibitory signal, preventing the killing of normal cells.

NK cell "licensing"

The process where NK cells gain killing potential through a prior interaction with a healthy cell via MHC class I/inhibitory receptor interactions.

NKT cells

Cells that possess an invariant TCR recognizing glycolipids presented by nonpolymorphic CD1d; they bridge innate and adaptive immunity and lack memory cell formation.

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)

A process where cytotoxic cells (MF, NK, Neutrophils, Eosinophils) bind to the Fc portion of an antibody that is already bound to a target cell to initiate killing.

Anergy

The state where self-reactive B cells are inactivated in peripheral lymphoid tissues rather than being deleted in the bone marrow.

Plasma Cell

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

Neutralization

An antibody function where the antibody binds to the antigen to block an active site, preventing it from binding to receptors on tissue cells.

Agglutination

The process where divalent antibodies bind to multiple antigens at once, forming cross-linked clumps of antigen/antibody complexes.

Precipitation

An antibody function similar to agglutination but involving soluble molecules, causing them to fall out of solution.

PLAN OP

A mnemonic for antibody functions: Precipitation, Lysis (via complement), Agglutination, Neutralization, Opsonization, and Phagocytosis.