Microbiology and immunology 22

• Antibodies are also called immunoglobulins
• Antibodies are large y-shaped secreted glycoproteins.
• Antigens can be proteins, polysaccharides, lipids, even nucleic acid
• Basic unit of antibodies: 2 identical heavy chains + 2 identical light chains, joined by non-covalent interactions and disulphide bridges.
• Each chain of an antibody has an N-terminal variable region and a C-terminal constant region.
• Antibody is secreted by mature B cells, but first expressed as a membrane-bound B cell receptor (BCR) in developing B cells.
• Cleavage of antibodies (immunoglobulins) occur at the hinge region
• Fab (Fragmented Antigen Binding) contains antigen-binding region.
• Fc (Fragment Crystalizable) interacts with Fc receptors on cells and with C1q.
• Main functions of antibodies: binds specifically to epitopes on the pathogen/antigen that elicit the immune response, either neutralization or opsonization.
• function of antibodies: recruit cells and molecules to destroy the pathogen/antigen.
• Antibody Fab region binds to epitopes on pathogens/ antigens.
• Epitopes can be linear, conformational components of a protein, or a combination of both.
• Antigens can be macromolecules that are free/secreted.
• The combination of the unique structure of the fab region and a range of non-covalent forces allow antibodies to bind to Antigens with very high affinities.
• Examples of non-covalent forces- electrostatic forces, hydrogen bonds, Van der waals forces, Hydrophobic forces, cation-pi interaction.
• Functions of antibodies: Neutralize, opsonise, agglutinate, activate complement, improve phagocytosis, Antibody-dependent cell cytotoxicity (ADCC), degranulation.
• Antibody's function to neutralize is to bind to bacteria/ virus surface or bacterial toxin, prevent interaction with cell receptors, prevents uptake of pathogen by target cells and rather; uptake and destruction by macrophages.
• opsonization is the process of extracellular proteins (Antibodies) binding to mark pathogen for destruction via phagocytosis.
• Direct opsonization is the binding of antibody contact region (Fc receptors) to phagocytes receptors
• indirect opsonization involves increasing complement (C3b) deposition on pathogen and binding to complement receptors (CR1)
• Degranulation is the immediate response of tissue mast cells to wounding, releasing preformed mediators, release of granules.
• Degranulation occurs via Fc receptors (FcR)
• Antibody can be cultured and produced in the lab by fusing an individual B cell with a B tumour line that grows indefinitely in culture, this generates a hybridoma.
• Use of antibodies- Lateral Flow Strips, Enzyme-linked immunosorbent assay (ELISA).
• We can use antibodies for flow cytometry, western blot, and immunofluorescence.