Definition: Immunochemistry is the branch of biochemistry that studies the chemical properties of immune reactions, particularly antigen-antibody interactions at a molecular level. It combines principles from immunology and biochemistry to explore and utilize the interactions between antigens and antibodies for diagnostic, therapeutic, and research purposes.
Key Components in Immunochemistry:
1. Antigens (Ag):
Definition: Substances (proteins, polysaccharides, lipids, nucleic acids) that provoke an immune response.
Types:
Exogenous (foreign antigens)
Endogenous (from body’s own tissues, sometimes auto-antigens)
Epitope: Specific part of antigen recognized by antibodies.
2. Antibodies (Immunoglobulins, Ig):
Structure: Y-shaped proteins produced by plasma cells (activated B cells).
Structure:
Two heavy chains and two light chains.
Variable region (Fab region) binds specifically to antigen.
Constant region (Fc region) mediates effector functions.
Types: IgG, IgM, IgA, IgE, IgD.
2. Antigen-Antibody Interaction:
Highly specific binding occurs through non-covalent interactions:
Hydrogen bonds, electrostatic interactions, hydrophobic interactions, Van der Waals forces.
Affinity: Strength of interaction between a single antigenic determinant and a single antibody binding site.
Avidity: Overall binding strength between antibody and antigen (multiple binding sites).
Biochemical Principles in Immunochemistry:
1. Specificity:
Antibody-antigen interactions are highly specific, relying on complementary shapes and biochemical interactions (hydrogen bonds, electrostatic interactions, hydrophobic interactions).
2. Affinity and Kinetics:
Affinity: Measured by the equilibrium dissociation constant (Kd).
Strong affinity: Leads to stronger and longer-lasting immune responses.
2. Non-Covalent Interactions:
Hydrogen bonds, ionic interactions, Van der Waals forces, and hydrophobic interactions facilitate antibody-antigen binding.
3. Epitope (Antigenic Determinant):
The precise region on the antigen recognized by antibodies.
Methods and Techniques in Immunochemistry:
1. Immunoassays:
ELISA (Enzyme-linked Immunosorbent Assay):
Detects antigens or antibodies using enzyme-labeled antibodies.
Used for disease diagnosis, hormone measurement, drug screening, etc.
2. Immunofluorescence (IF):
Antibodies tagged with fluorescent molecules detect antigens in tissues or cells under a fluorescence microscope.
Direct IF: Fluorophore-labeled antibody binds directly to antigen.
Secondary antibodies: Bind to primary antibodies; conjugated with detection molecules (enzymes, fluorophores).
Conjugates: Antibodies linked chemically to enzymes or fluorescent dyes for visualization.
Biochemical Importance in Nursing and Medical Field:
Disease Diagnosis: Immunochemistry techniques (ELISA, IF, western blotting) used in diagnosis of infectious diseases, autoimmune disorders, and cancer biomarkers.
Therapeutic Monitoring: Measuring drug concentrations, hormones, tumor markers.
Research Applications: Studying pathogenesis, drug discovery, and vaccine development.
Clinical Applications:
Immunohistochemistry: Identification of tumor markers (e.g., HER2, ER, PR in breast cancer).
Western Blotting: Confirmatory test in HIV diagnosis.
ELISA: Screening tests for infectious diseases (HIV, Hepatitis).
Applications in Nursing and Health Sciences:
Understanding disease pathology and management.
Drug monitoring (therapeutic drug monitoring).
Vaccine evaluation and immunogenicity testing.
Research on immune system disorders.
Future Perspectives in Immunochemistry:
Advanced biosensor technologies.
Development of monoclonal antibodies and targeted immunotherapies.
Personalized medicine based on immunochemical markers.
Immunochemistry: Structure, Functions, and Biochemistry of Immunoglobulins (Antibodies)
What are Immunoglobulins?
Immunoglobulins (Ig), commonly known as antibodies, are specialized glycoproteins produced by plasma cells (activated B-lymphocytes). They play a critical role in the immune response by recognizing and neutralizing pathogens such as bacteria and viruses.
Biochemical Structure of Immunoglobulins
Each immunoglobulin molecule is composed of four polypeptide chains:
Two Heavy (H) chains: (~50-75 kDa each)
Two Light chains: (Kappa κ or Lambda λ; about 25 kDa each)
The heavy and light chains are linked by disulfide bonds.
Basic Structure:
Y-shaped molecule:
Two identical antigen-binding sites (Fab regions).
A constant region (Fc region) responsible for biological functions.
Domains:
Variable (V) region: Contains antigen-binding sites; varies between antibodies.
Constant region (C region): Responsible for mediating biological functions.
Heavy Chains (5 types/classes):
Each immunoglobulin type is named according to the heavy chain type:
Immunoglobulin
Heavy Chain
Subtypes
IgG
Gamma (γ)
γ1, γ2, γ3, γ4
IgM
Mu (μ)
–
IgA
Alpha (α)
α1, α2
IgD
Delta (δ)
–
IgE
Epsilon (ε)
–
Classes and Functions of Immunoglobulins:
1. IgG (Gamma globulin)
Structure: Monomer (single Y-shaped unit)
Concentration: Most abundant antibody in plasma (~75% of serum antibodies).
Function:
Main antibody in secondary immune response.
Opsonization (enhances phagocytosis).
Neutralization of toxins and viruses.
Crosses placenta providing passive immunity to the fetus.
Activates complement system.
2. IgM (Macroglobulin)
Structure: Pentamer (5 Y-shaped units linked by J-chain)
Concentration: ~10% of serum antibodies.
Function:
Primary immune response antibody.
First antibody produced during infection.
Strongly activates complement system.
Indicator of recent infection.
3. IgA (Secretory antibody)
Structure:
Monomer in serum, Dimer in secretions (tears, saliva, breast milk, mucus).