Exam I - Antigens and Antibodies

Antigen

substance that induces the production of antibodies. Must be recognized as non-self in order to elicit an immune response. Are typically large proteins.

Immunogenicity

ability of an antigen to provoke the production of antibodies

Haptens

small molecules that do not elicit antibodies production unless bound to a carrier protein. Ie) lipids

less

Amino acid homopolymers (polymers that are made up of identical monomers) are (more or less) immunogenic than heteropolymers (polymers that are made up of several difference monomers).

structure

genetic composition of the host

antigen concentration

three factors determining immunogenicity of a substance.

Immunogen

antigen which is a macromolecule (proteins, polysaccharides) that provokes an immune response when introduced into the body.

Tolerogen

antigen that does not typically elicit an immune response due to its molecular form, but can become an immunogen if its molecular form is changed

Allergen

any substance that causes an allergic reaction. Can be eaten, inhaled, injected, or come into contact with skin.

Exogenous antigens

antigens that have entered the body by an external source. Ie) inhalation, ingestion, or injection.

Endogenous antigens

antigens that are generated within the cell as a result of normal cell metabolism or by infection.

T independent antigens

antigens that can directly stimulate B cells to produce antibodies without the help of T cells. Have the same antigenic determinant repeating many times. Ie) Polysaccharides

T dependent antigens

antigens that stimulate the production of antibodies with the help of T cells. Are characterized by a few copies of many different antigenic determinants Ie) proteins

Hapten carrier conjugates

complex of a immunogenic carrier and hapten which are covalently linked. Have native antigenic determinants of the carrier as well as by the hapten.

Autoantigens

a normal protein or complex of proteins recognized by the immune system of patients suffering from autoimmune disease. Under normal conditions, these antigens do not elicit an immune response. This can change due to genetic and environmental factors.

Tumor specific antigens

antigens presented by MHC I or MHC II molecules on the surface of tumor cells. Are recognized by T lymphocytes which then destroy the tumor cells.

Histocompatibility molecule

molecules that present antigens on a cell surface to the surrounding environment. Interact with immune cells to cause an immune response.

Proteins > polysaccharides > nucleic acids > lipids

order these macromolecules from most to least immunogenic

polysaccharides

lipids

Proteins

nucleic acids

complex structure

Proteins are very good immunogens due to...

poor

Nucleic acids are generally (good or poor) immunogens, but become more immunogenic when single stranded or combined with proteins.

no

are lipids immunogenic?

good

Polysaccharides and lipopolysaccharides are generally (good or poor) immunogens. Ie) LPS expressed by some bacteria

Antigenic determinants

limited portion of the antigen created by the primary sequence of the polymer which is presented to B cells and antibodies. Limited to about 4-8 resides, very small.

Antibodies

immunoglobulins that react specifically with the antigen that stimulated their production. Makes up about 20% of plasma proteins.

Polyclonal antibodies

antibodies that are heterogenous because they are formed by different B cell lineages within the body. They arise in response to a single complex antigen and are a collection of immunoglobulin molecules that react against a specific regions (epitopes) of the antigen.

Monoclonal antibodies

antibodies that are homogenous because they arise from a single clone of cells in a plasma cell tumor. They are produced by fusing a myeloma cell with an antibody producing lymphocyte. This produces unlimited quantities of antibodies in vitro that can only react against a single antigenic determinant

25,000

The light polypeptide chains of an antibody are about how many Da?

constant

Kappa or lambda forms of light chains are determined by amino acids differences in their _____ regions. These forms are found in all classes of immunoglobulins

antigen binding

amino terminal of each light an heavy chain participates in the...

one

how many variable domains do light chains of immunoglobulins have?

one

how many constant domains do light chains of immunoglobulins have?

one

how many variable domains do heavy chains of immunoglobulins have?

three or more

how many constant domains do heavy chains of immunoglobulins have?

five (Gamma, mu, alpha, delta, and epsilon)

how many forms do heavy chains of immunoglobulins have? They are variable depending on the antibody.

Fc fragment

fragment of the heavy chain which is a carboxyl terminal that participates in complement fixation and binding to cell surface receptors.

disulfide bridges

Light chains and heavy chains of an antibody are linked by...

Domain

specialized region of protein having a three dimensional shape with a specified function.

110

Each domain of an immunoglobulin is about how many amino acids long?

Variable regions

domain of an immunoglobulin responsible for binding of the antigen

Constant regions

domain of an immunoglobulin responsible for biologic functions. Ie) binding to complement, interacting with immune cells.

Hypervariable region

subregion of an immunoglobulin present within the variable regions of both L and H chains. Consists of extremely variable amino acid sequences that cooperate in space to form the antigen binding site. Only made up of about 5-10 amino acids.

IgG

divalent immunoglobulin made up of two light and two heavy chains. It is the predominant in secondary immune responses during defense against bacteria and viruses. Mediates opsonization of the antigen which allows for phagocytosis.

divalent

describe the structure of igG

IgG

opsonization is the coating antigen with antibody which enhances phagocytosis. Which immunoglobulin mediates this function?

IgG

what is the most abundant immunoglobulin in newborns?

Fc receptors

receptors found on macrophages and other cells which recognize infected cells to initiate phagocytosis.

four

IgG has how many subclasses depending on amino acid sequence differences in the H chain constant region and the number/location of disulfide bonds

IgG1

the most abundantly occurring subclass of IgG.

IgG2

the subclass of IgG which plays an important role in host defense against bacterial infection.

IgG3

the subclass of IgG which is an effective activator of complement.

IgG4

the subclass of IgG which does not activated complement due to its compact structure.

IgM

pentamer immunoglobulin which is made up of five IgG units having ten antigen binding sites total. It is the main immunoglobulin produced early in the primary immune response located on all uncommitted B cells. Functions in agglutination, fixing of complement, and antigen-antibody reactions.

pentamer, five IgG units

describe the structure of IgM

Agglutination

clumping of bacteria in the presence of antibodies mediated by IgM

IgM

Agglutination, the clumping of bacteria in the presence of antibodies is mediated by which immunoglobulin?

intrauterine infection

Evidence of immunoglobulin IgM in a fetus or newborn indicates an...

IgA

dimer immunoglobulin made up of two units (H2L2) joined by a J chain with a surrounding secretory component. Is the main immunoglobulin responsible for mucosal immunity protecting mucous membranes from bacterial and viral infections. Found in secretions such as milk, saliva, tears, etc.

dimer

describe the structure of IgA

IgA

which immunoglobulin functions in the protection of mucous membranes from bacterial and viral infections?

Poly-Ig receptor

receptor which is cleaved to form the secretory component of IgA. Functions in the transport of IgA across mucosal epithelial cells and the joining of IgA dimers to one another.

IgA1 and IgA2

what are the two subclasses of IgA?

protease, antibody mediated resistance

Some bacteria such as Neisseria can destroy IgA1 via production of a ______ or by developing _____

IgE

immunoglobulin whose Fc region binds to mast cells, basophils, and eosinophils acting as a receptor for antigens to trigger an immediate (anaphylactic) allergic response via the release of mediators. Not typically present in high levels.

IgE

what immunoglobulin mediates allergic response?

IgD

immunoglobulin which acts as an antigen receptor present on B lymphocytes although its function is not clear. Only present in trace amounts.

IgA

what is the most abundant immunoglobulin in the tear film?

IgA and igg

what two immunoglobulins are found in the aqueous humor?

igg

what is the most abundant immunoglobulin in the aqueous humor?

anterior chamber

In the eye, there are no antibodies beyond the...

2

what is the valency of IgG?

4

what is the valency of IgA?

10

what is the valency of IgM?

2

what is the valency of IgD?

2

what is the valency of IgE?

IgG

what immunoglobulin has the highest serum concentration?

IgE

what immunoglobulin is found in the serum only in trace amounts?

IgM

what immunoglobulin has the highest complement fixing capacity?

IgG

what is the only immunoglobulin that can cross the placental barrier?

Chromosome 14

chromosome which contains the genetic information for the heavy chain family of immunoglobulins

22 and 2

Multigene families of immunoglobulins are also located on these two chromosomes

VDJ recombinases

enzymes responsible for gene recombination process during B cell differentiation. Remove introns and join the remaining exons.

2

The variable region of each light chain is encoded by how many gene segments?

3

The variable region of each heavy chain is encoded by how many gene segments?

variable gene

The gene segments derived from each heavy and light chain is brought together to form a single functional...

constant gene

Variable gene is transcribed with the appropriate...

light chains

which chains of the immunoglobulin are synthesized first?

disulfide bonds

Light and heavy chains are joined by these bonds

Carbohydrate moiety

is added by the golgi apparatus and then released by the cell

Somatic recombination

the genetic rearrangement which helps in the production of many different antibodies.

Clonal Selection

the formation of B cell clones binding to a specific antigen. They differentiate into plasma cells to secrete antibodies that correspond to that antigen.

major histocompatibility complex

proteins found on the surfaces of antigen presenting cells that help the immune system recognize foreign materials.

Antigen presenting cells

cell that present antigens via a major histocompatibility complex to helper T cells or B cells directly.

Helper T cells

cells that transport antigens from antigen presenting cells to the receptors found on B cells.

B cells

cells that display a single homogenous clonal molecule on their surface which then serves as a receptor for specific antigens. These cells can only respond to a single antigen or a closely related group of antigens.

IgM, IgD, Fc, complement

All immature B cells carry this immunoglobulin on their surface, and sometimes ____ as well. They also have receptors for the ___ portion of the antibody as well as several _____ components.

Opsonization

process by which an organism is coating in antibodies to enhance phagocytosis by making the organism susceptible to ingestion and destruction by phagocytic cells. Especially useful against organisms which have a polysaccharide capsule which are otherwise difficult to phagocytize

Complement mediated lysis

binding of antibodies to viral proteins on virus infected cells resulting in complement fixation and cell lysis.

Antibody dependent cell cytotoxicity

the attachment of antibodies to viral proteins on a virus infected cell which leads to interaction with a killer cell and lysis of the virus infected cell.

non-covalent forces

Antigen antibody reactions involve what type of forces?

B cells and T cells

Antibodies are found on the surface of these two cell types