immunology and serology review antibody structure and function exam 1

memorize this set

Antibody functions

• Neutralization (binding inhibits activity)

• Opsonization (enhances phagocytosis)

• Complement activation (triggers complement activity)

• Antibody-dependent cell-mediated cytotoxicity (ADCC)

• Cells (NK cells, macrophages, neutrophils) recognize antibody bound to target cell and release substances to destroy target cell.

What is the function of CSFs? Colony stimulating factors?

Induce and control differentiation of cells in bone-marrow.

What are the classes (isotypes) of antibody

IgM, IgG, IgA, IgE, IgD

What is the definition of an antibody

Antibodies (immunoglobulin) are proteins that specifically binds to an antigen and targets its destruction

What band do antibodies normally appear? And what is their serum electrophoresis pH?

gamma (γ) band with serum electrophoresis at pH 8.6

gammaglobulin is enriched with

antibody

Basic structure of an antibody

Two heavy chains and two light chains held together by disulfide bonds, the chains are divided into domains

The variable and constant regions do what?

They function to specify the antibody

Variable region- binds to specific antigen

Constant region- determines Ab immunoglobin class

Types of light chains

Kappa and lambda

Light chains are secreted by what type of cells?

Malignant plasma cells

Type of heavy chains determines

The class of antibody

IgG: γ chain IgM: μ chain IgA: α chain IgD: δ chain IgE: ε chain

Match the immunoglobulin type to their heavy chain

IgG: gamma chain

IgM: mu (ul) chain

IgA: alpha chain

IgD: delta chain

IgE: epsilon chain

Isotype Definition

A unique amino acid sequence that is common to all immunoglobulin molecules of a given class in a given species

Define Allotypes

Minor variations of isotype sequences that are present in some individuals but not others

Idiotype Definition

Variations in variable regions that give individual antibody molecules specificity it is located on the antibody’s variable region or on the T cell receptor

Compare the difference between the different proteolytic cleavages by papain and pepsin

Fab stands for? Location? What does it do

Fragment antigen binding ; variable region; antibody specificity

Fc stands for? Function?

fraction Crystallized, the constant region, confirms the antibody function

Provide two examples of the clinical usefulness of Fab fragments

• Neutralizing antibodies

(Rattlesnake venom, Digoxin overdose)

• Small and pass through the kidneys

(eliminated in urine)

Which antibody classes are found in monomers?

IgG and IgE

Which antibody classes are found in multimers held together by J chain?

IgM and IgA

Which antibody class is found in pentamers and monomers?

IgM

Which antibody is found in multimers made up of dimers and monomers?

IgA

B cell receptor Is _______ with membrane component

monomeric

Predominant immunoglobulin in humans percentages (75% to 80% of the total serum immunoglobulins)

Four subclasses:

IgG1: 66%

IgG2: 23%

IgG3: 7%

IgG4: 4%

Which antibody has the longest half life

IgG has longest half life, 23 days

Major Functions of IgG

Providing immunity for the newborn (because IgG can cross the placenta)

• Fixing complement

• Coating antigen for enhanced

phagocytosis (opsonization)

• Binding to cells for antibody- dependent cellular cytotoxicity (ADCC) by NK and other cells

• Neutralizing toxins and viruses

• Participating in agglutination and precipitation reactions

IgG role with toxins, it’s relationship with blood cells

All subclasses can cross the placenta

• Macrophages, monocytes, and neutrophils have Fc receptors specific to the Fc region of IgG, increasing the efficiency of phagocytosis

• A high diffusion coefficient allows IgG to enter extravascular spaces more readily than other immunoglobulin types

• IgG plays a major role in neutralizing toxins and viruses

What Trait of IgG allows it to enter extravascular spaces more readily than other immunoglobulin types?

It has a high diffusion coefficient

IgM Characteristics

Known as a macroglobulin

Has a molecular weight of about 900,000 d

Accounts for 5% to 10% of all serum immunoglobulins

No memory cells

Synthesized as long as antigen is present

Has half-life of 6 days (much shorter than that of IgG)

Can exist as:

Monomer (on surface of B cells) Pentamer (found in secretions)

what best describes the IgM’s form and structure

Pentamer form

Held together by J chains, which are linkage points for disulfide bonds between two adjacent monomers

Has a star-like shape with 10 antigen-binding sites

Where is IgM mainly found?

Intravascular pool

Can IgM cross the placenta?

No

Which immunoglobulin appears first after antigenic stimulation?

IgM

Which antibody is also known as the primary response antibody?

IgM

Can IgM cross placenta? Does it have memory cells?

No bc it’s too large, no memory cells

Known as the primary response antibody

IgM, Appears first after antigenic stimulation and in the maturing infant

Synthesized only as long as antigen remains present due to lack of memory cells so it cannot make a secondary response

Functions of IgM

• Complement fixation

• Helps with opsonization due to it’s ability to activate complement.

• Some complement components are opsonins, e.g. C3b

• Agglutination

• Toxin neutralization

IgA characteristics in serum

Accounts for 10% to 15% of all circulating immunoglobulins in serum

One variable and three constant regions

Serum IgA: Appears as a monomer with a molecular weight of approximately 160,000

Secretory IgA (sIgA)

Is synthesized in plasma cells found mainly in mucosal-associated lymphoid tissue and beneath mucosal epithelium.

Is released in dimeric form

Is captured by poly-Ig receptor which transports it across epithelial cells.

When released, the IgA has part of the poly-Ig receptor still attached.

The part derived from receptor remaining is called secretory component (SC)

Function of IgA

• Patrols and acts as the first line of defense in mucosal surfaces

• Neutralizes toxins produced by microorganisms

• Prevents bacterial adherence to mucosal surfaces

• Found in breast milk and passively transfers immunity to newborn during breastfeeding

What antibody is found in breast milk?

IgA

IgD Characteristics in serum

Extremely scarce in the serum

Found on the surface of immunocompetent but unstimulated B lymphocytes

Appears second (after IgM)

May play a role in B-cell activation

Plays a role in regulating B-cell maturation and differentiation

Secreted form in serum does not appear to serve a protective function

Does not bind complement

Does not bind to neutrophils or macrophages Does not cross the placenta

IgE characteristics

0.0005 % of total serum immunoglobulins

• Produced by plasma cells that are located

primarily in the lungs, gut and skin

• Does not participate in complement fixation, agglutination, or opsonization

• Is incapable of crossing the placenta

• Attaches to basophils, eosinophils and tissue mast cells through high-affinity Fc ε RI

receptors

IgE Function: Allergic Reactions

Two adjacent IgE molecules on a mast cell bind a specific antigen

Cascade of cellular events results in degranulation of mast cells and release of vasoactive amines (such as histamine and heparin)

Induce allergic type reactions Helps expel parasites

Type I immediate hypersensitivity results in what conditions

Hay fever, asthma, vomiting and diarrhea, hives, life-threatening anaphylactic shock

IgE Involvement in Parasitic Infections

Eosinophils play a major part in the destruction of large antigens, such as parasitic worms, that cannot be easily phagocytized. Eosinophils recognize IgE bound to parasite

Which immunoglobulin is involved in type I immediate hypersensitivity reactions?

IgE

B cell receptor

• Antibody monomer has transmembrane anchor

• Igβ & Igα transmit signal

• Can have heavy chains from any of the antibody classes.

• Doesn’t matter what the class, B cell receptor is still a monomer

Affinity Definition

binding strength between an antibody and a single antigenic determinant (epitope)

Avidity Definition

number of antibody-combining sites and the number of epitopes in a single antigen

Monoclonal Antibodies

Mainly used for diagnostic testing and therapeutic purposes

In vitro diagnostic testing

Delivery of therapeutic agents in diseases

Developed based on knowledge that B cells are genetically preprogrammed to synthesize very specific antibody

Are derived from a single parent antibody- producing cell that has reproduced many times

Hybridoma

Fusion of plasma cell with a laboratory-grown myeloma cell deficient in Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)

The myeloma cells require special medium to grow, but the plasma cells have a functional HGPRT gene.

Hybridoma will be immortal and will not need special medium

Hybridoma produces antibody with the specificity of the plasma cells indefinitely

Hybridoma Production involves

Immunizing a mouse with a certain antigen

Harvesting spleen cells

Spleen cells are fused with myeloma cells using polyethylene glycol (PEG)

Selecting fused cells and screening for presence of desired antibody

High affinity Vs Low affinity:

• High affinity: tightly bind antigen at lower concentration

• Low affinity: better when a large amount of antigen is present)