Immunopathology: Antigen Receptors of Lymphocytes

Vocabulary-style flashcards covering the properties, structures, and functions of B and T cell receptors, antibody isotypes, and monoclonal antibody therapy as presented in the Immunopathology lecture.

B cell receptor (BCR)

A complex consisting of membrane-bound antibodies and Ig\text{̑}\text{̑} and Ig\text{̑}\text{̒} signaling chains that recognizes shapes or conformations of free or bound macromolecules.

T cell receptor (TCR)

A membrane-bound heterodimeric protein composed of an \text{̑} chain and a \text{̒} chain that recognizes peptides bound to major histocompatibility complex (MHC) molecules.

Immune repertoire

The total number of distinct lymphocyte clones within an individual.

Variable (V) region

The portion of antigen receptors that contains highly variable sequences responsible for antigen recognition.

Constant (C) region

The conserved portion of antigen receptors; in antibodies, the C regions of the heavy chain determine the isotype and effector function.

Hypervariable regions (CDRs)

Three short segments within the V regions of both antibodies and TCRs, also known as complementarity-determining regions, that provide the greatest variability for antigen binding.

CDR3

The most variable of the three hypervariable regions, located at the junction of the V and C regions, which contributes most to antigen binding.

Fab (Fragment, antigen-binding)

The portion of an antibody containing a whole light chain and the V and first C domains of a heavy chain; it is required for antigen recognition.

Fc (Fragment, crystallizable)

The portion of an antibody containing the remaining heavy-chain C domains responsible for biologic activity and effector functions.

Hinge region

A flexible segment linking the Fab and Fc regions, enabling the antibody to simultaneously bind antigen epitopes separated by varying distances.

Antibody Isotypes

The five classes of antibodies determined by their heavy (H) chains: IgM (\text{̓}), IgD (\text{̔}), IgG (\text{̕}), IgE (\text{̖}), and IgA (\text{̑}).

Light (L) chains

The two types of polypeptide chains in an antibody, called \text{̚} and \text{̛}, which differ in their C regions; an antibody has either two \text{̚} or two \text{̛} chains, but never one of each.

Epitopes

The specific parts of antigens that are recognized by antibodies; also called determinants.

Linear epitopes

Epitopes of proteins that form a contiguous stretch of amino acids recognized by an antibody.

Conformational epitopes

Epitopes formed by the distinct shape of a folded protein recognized by an antibody.

Affinity

The strength at which an antibody binds to a single epitope, commonly measured by the dissociation constant ($K_d$).

Affinity maturation

The process by which the affinity of antibodies increases with repeated stimulation, typically moving from a $K_d$ of $10^{-6}$ to $10^{-9}\text{ }M$ to a $K_d$ of $10^{-8}$ to $10^{-11}\text{ }M$.

Avidity

The total strength of binding by an antibody to an antigen, which is greater than the affinity of a single antigen-antibody bond.

Cross-reactivity

The phenomenon where an antibody produced against one antigen binds to other, structurally similar antigens.

Hybridomas

Fused cells created from spleen B cells and immortal myeloma cells that are cultured in selection medium to produce monoclonal antibodies.

CD3 and ̙ proteins

A group of proteins associated with the TCR that initiate biochemical signaling upon antigen recognition.

Monoclonal antibodies (mAbs)

Pure antibodies with a single specificity produced by a single clone of hybridoma cells.

Rituximab (Target: CD20)

A monoclonal antibody used for B cell depletion in diseases such as Rheumatoid arthritis, multiple sclerosis, and B cell lymphoma.

Trastuzumab (Target: HER2/Neu)

A monoclonal antibody used to inhibit growth signaling in HER2-positive breast cancer.

Bevacizumab (Target: VEGF)

A monoclonal antibody that blocks tumor angiogenesis, used in treating breast cancer and colon cancer.