Antibodies and Antigens Lecture

Comprehensive vocabulary flashcards covering the structure, types, functions, and enzymatic digestion of antibodies, as well as the characteristics of antigens.

Antibodies

Also called immunoglobulins, these are proteins that form part of the globulin portion of blood and are utilized by the immune system.

Naive cells

Term used to describe B cells and T cells before they have been activated by an encounter with an antigen.

Plasma cells

Differentiated B cells that produce free antibodies.

Gamma globulins

The specific portion of blood proteins in electrophoresis to which antibodies belong.

Heavy chain

The bigger of the two chains forming an antibody, composed of both a constant region and a variable region.

Light chain

The smaller of the two chains forming an antibody, composed of both a constant region and a variable region.

Variable region

The lighter region located at the ends of the antibody arms that serves as the antigen binding site.

Somatic recombination

The process that dictates the initial shape of the variable region before contact with an antigen occurs.

Hinge region

The part of the antibody that allows for flexibility, enabling the molecule to vary the degree to which it is open.

Papain

An enzyme that digests the antibody at the hinge region, resulting in two $Fab$ fragments and one $Fc$ fragment.

Pepsin

An enzyme that digests the antibody below the hinge region, resulting in one $F(ab)_2$ fragment and one $Fc^{\prime}$ fragment.

Fab (antigen binding fragment)

The fragments of an antibody produced by enzymatic digestion that are capable of binding to an antigen.

Fc (crystallizable fragment)

The portion of the antibody responsible for determining biological activity, such as marking antigens for immune cells like phagocytes or natural killer cells.

Isotype

Differences in the heavy chain constant region; examples include $IgA$, $IgG$, and $IgM$.

Allotype

Unique differences within the constant regions of gamma and alpha heavy chains, and kappa light chains, present in different individuals.

IgG

The smallest antibody and the only one that can cross the placenta; it is involved in opsonization, ADCC, and activating the classical complement pathway.

IgM

The first antibody produced during an infection; it exists as a monomer on naive B cells or as a large pentamer in serum.

J chain

The protein component that joins five antibody monomers together to form the pentameric version of $IgM$.

2-mercaptoethanol and Dithiotreitol

Chemical substances used to break the pentameric structure of $IgM$ into individual molecules.

Primary immune response

The body's response to the first encounter with an antigen, characterized by a long lag phase and the initial rise of $IgM$.

Secondary immune response

The subsequent response to an antigen which has little to no lag phase and produces very high levels of $IgG$.

IgA

The antibody found primarily in mucosal secretions including mucus, tears, saliva, and colostrums.

MALT (Mucosa Associated Lymphoid Tissues)

The area where the activation of B cells leading to $IgA$ production primarily occurs.

IgD

An antibody present on the cell surface of naive B cells, though its exact function remains largely undetermined.

IgE

Also known as the reaginic antibody, it is responsible for allergies, anaphylactic reactions, and immune responses to parasites.

Immunogens

Macromolecules that are always capable of triggering an adaptive immune response.

Hapten

Low molecular weight substances that do not evoke an immune response unless bound to a carrier molecule.

Antigen Immunogenicity Rank

Proteins (most immunogenic), followed by Polysaccharides, Nucleic acids, and Lipids (least immunogenic).

Molecular weight threshold

Antigens generally must have a weight of $\text{10,000 daltons}$ or higher to be effective.

Epitope

The specific part of an antigen that is recognized by the immune system.