“Learning without thinking is useless; thinking without learning is dangerous.” THE COMPLEMENT SYSTEM. ANTIBODIES – CLASSIFICATION AND STRUCTURE. MAJOR CLASSES Professor Victoria Sarafian, MD, PhD, DMSc Complement - a complex of plasma proteins (30) with enzymatic function, which are activated consecutively in a cascade manner. Proteases! Main factor – C3 lectins - sugar-binding proteins in plants, animals and bacteria; some bacteria use lectins to attach themselves to the cells of the host organism. Classical pathway Lectin Alternative pathway Аg-Аb-complexes pathway Bacterial products (IgM, IgG) Adaptive Innate immunity immunity 4. inflammation ANTIBODIES Аbs - Immunoglobulins, proteins – serum gamma-globulins They are secreted by Pl after Ag-stimulus. Molecular weight – 150-900 кDa STRUCTURE – the 4-chain basic unit composed of 4 polypeptide chains 1 2 2 epitopes paratope V-domain С-domain Structure 2 light chains (L) Variable - domain 2 heavy chains (H) Constant - domain Hypervariable domains Disulphide bridges Hinge region Paratope = N-end Аg-binding site V-domain hypervariable disulphide Complementary chain hinge interaction С-fragment epitope – paratope С-end Fab-fragment – binds the Ag; builds the paratope. Fc-fragment – determines the biological activity of the Ab. papain pepsin ► heavy chains - , , , , - they determine the Ab class! Each Ab molecule contains just one type of heavy chain! IgG - IgM - IgA - IgE - IgD - ►light chains - , Each Ab molecule contains just one type of light chain! Each Ab molecule contains 2 identical H- chains and 2 identical L-chains! Antibody classes IgG monomer participates mainly in the secondary immune response crosses the placenta activates the complement acts as an opsonin IgA – serum and secretory monomer; dimer; trimer participates mainly in the secondary immune response is secreted in colostrum and in mother’s milk defends the mucosa opsonin J-chain IgM J-chain participates mainly in the primary immune response appears first in evolution and in ontogenesis strongest agglutinating ➢ Pentameric form - capacity secretory IgM opsonin ➢ Monomeric form – activates the complement membrane-bound IgM – receptor on В- cells IgE monomer binds to Fc- receptors on basophils and mast cells – allergic reactions opsonin IgD monomer Receptor for the Ag on В-cells Functions Аbs do not destroy directly the Ag! They only help its elimination! MECHANISM OF ANTIBODY ACTION Do not destroy directly the Ag! 1. Agglutination - IgM J-chain 2. Precipitation 3. Neutralization - Bacterial toxins Maf 4. Opsonization Compl. 5. Complement activation 6. ADCC – Ab-dependent cellular cytotoxicity 7. Allergic reactions – IgE, IgG4 Nobel Prize -1984 Hybridoma technology Georges Kohler Cesar Milstein Production of monoclonal antibodies (Mabs) (hybridoma technology) Polyclonal Abs Monoclonal relatively nonspecific antibodies (МAbs) • Released in the serum of highly specific humans or animals, • Produced by the injected with an Ag. hybridoma technology. • They are a mixture of • They are a mixture of Abs, produced due to the Abs produced due to the differentiation of differentiation of a different B-cell clones. single B-cell clone. • Recognize different • Recognize a single epitopes of the Ag epitope of the Ag molecule. molecule. • Used for diagnostics, • Used for diagnostics and prophylactics and therapy? therapy. • Humanized • MAbs are produced by antibodies - Abs from recombinant DNA non-human species technology, then the with modified AA construct is expressed sequences in order to in mammalian cells increase their similarity to Abs mouse chimeric produced naturally in humans human Cetuximab - EGFR inhibitor used treatment of Chimeric/ metastatic CRC humanized.