Antibody CLS-415 Nada Mohamed Ahmed, MSc, MT (ASCP)i

Structure and function Nada Mohamed Ahmed, MD, MT (ASCP)i

Objectives Introduction Definition to antibody Structure of Ab Sub class of Ab (types) Function

Introduction Soluble glycoproteins found in the γ globulin of serum and sometimes in tissue fluids Ab specific recognition of Ag Immunoglobulin Ig determines biological structure of Ab.(poor Ab) Ab determines the function of Igs All Abs are must be Igs and not vice versa, some Igs are defective or poor Abs. However, both terms are used interchangeably.

Antibodies Proteins that recognize and bind to a particular antigen with very high specificity. Made in response to exposure to the antigen. Each antibody has at least two identical sites that bind antigen: Antigen binding sites. Definition

Definition of Antibodies Belong to a group of serum proteins called immunoglobulins (Igs). Valence of an antibody: Number of antigen binding sites. Most are bivalent.

Immunoglobulins

ANTIBODY STRUCTURE light chains An antibody molecule is composed of two identical Ig heavy chains (H) and two identical light chains (L), each with a variable region (V) & constant region (C).

Antibody Structure Immunoglobulins are glycoproteins made up of: - Four polypeptide chains (IgG): a- Two light (L) polypeptide chains b- Two heavy (H) polypeptide chains - The four chains are linked by disulfide bonds - Terminal portion of L-chain contains part of antigen binding site - H-chains are distinct for each of the five Immunoglobulins - Terminal portion of H-chain participate in antigen binding site - The other (Carboxyl) terminal portion forms Fc fragment

Antibody Structure

Light chain : made of two domains One variable domain VL determine specificity (Epitope) One constant domain CL they are two types of a.a. sequences in their constant domain 1- kapa or 2- lamda but never combined Heavey chain : made up 4 or 5 domains one variable domain VH 4Or 3 constant domain determines diversity CH

Sub class of Ab (types) In the middle of heavy chain there is area “hing region” flexible joint allow two Ag binding. When a.a. sequence in heavy chain ( determine class and subclass of Ab) μ = Μh = IgM γ=γh=IgG α= αIgA δ=δH=IgD ε=εH=IgE

Antibodies or Immunoglobulins * Five classes of Antibodies:  IgG  IgM  IgA  IgD  IgE

1.Opsonization of antigens. 2.Activation of the complement. 3.Neutralization of bacterial and viral toxins. 4.Enhancement or mediated allergic and inflammatory reactions.

Immunoglobulin Classes IgG Structure: Monomer Percentage serum antibodies: 80% Location: Blood, lymph, intestine Half-life in serum: 23 days IgG function : Complement Fixation: Yes Cross Placenta :Yes Enhances phagocytosis, neutralizes toxins and viruses, protects fetus and newborn.

Immunoglobulin Classes. IgM Structure: Pentamer Percentage serum antibodies: 5-10% Location: Blood, lymph, B cell surface (monomer) Functions: Half-life in serum: 5 days Complement Fixation: Yes Placental Transfer: No Known Functions: 1-First antibodies produced during an infection. 2- Effective against microbes and agglutinating antigens.

Immunoglobulin Classes. IgA Structure: Dimer Percentage serum antibodies: 10-15% Location: Secretions (tears, saliva, intestine, milk), blood and lymph. Half-life in serum: 6 days Complement Fixation: No Placental Transfer: No Known Functions Prevent attachment of bacteria and viruses to mucous membrane by secretary peaces Important for maternal immunity in colostrums during breast feeding

Immunoglobulin Classes. IgE Structure: Monomer Percentage serum antibodies: 0.002% Location: Bound to mast cells and basophils throughout body. Blood. Half-life in serum: 2 days Complement Fixation: No Placental Transfer: No Known Functions 1-play important role in Allergic reactions and hypersensitivity. 2- lysis of worms.

Immunoglobulin Classes IgD Structure: Monomer Percentage serum antibodies: 0.2% Location: B-cell surface, blood, and lymph Half-life in serum: 3 days Complement Fixation: No Placental Transfer: No Known Functions: In serum function is unknown. On B cell surface, initiate immune response. Serve as Ag receptor on B cell.