Antibodies and Antigens

• There are two pathways of complement activation: classic and alternative.
• Autoantigens are self antigens; the body should recognize these, but if it doesn't, auto-immune disease occurs.
• Immunogens are different from antigens in that they are large macromolecules, while antigens can be very small.
• An immune response is more likely to be triggered if the molecular weight is higher.
• The more complex the molecule, the more antigenic it is.
• Small molecules can be antigenic if they are attached to a larger carrier molecule, known as haptens.
• There are five distinct classes of immunoglobulin, each with subgroups such as IgG, IgM, IgA, IgD, IgE.
• Each antibody molecule consists of two heavy chains (H) and two light chains (L).
• Heavy chains consist of about 440 aa and 50-70k D.
• Light chains consist of about 220 aa and 20-25k D.
• Chains are held together covalently via molecular bonds, disulfide bonds, and noncovalent bonds
• Antibodies are bifunctional, each with two identical Fab pieces.
• The crystallizable fragment (Fc) consists of two ends of the heavy chain.
• Antibodies can be split into Fc and Fab in the hinge region by proteolytic enzymes.
• Affinity indicates higher specificity than avidity.
• Pepsin is used to help determine the function of the chain parts.
• IgE binds to mast cells and basophils; it has allergy and antiparasitic activity.
• IgE is made up of 2 kappa or lambda light chains and 2 epsilon heavy chains
• Avidity refers to the strength of all interactions combined; IgM typically has high avidity as it has ten binding sites.
• IgG can cross the placenta and has a long half-life.
• The strength, which an antigen-antibody immune complex possesses at that epitope is referred to as avidity.
• Affinity refers to the strength of a single antibody-antigen interaction; each IgG antigen binding site typically has high affinity for its target.
• IgG binds to phagocytes; it is the main blood antibody for secondary responses and crosses the placenta.
• Many complement proteins are enzymes or proteinases.
• Foreign blood antigens and recipient antibodies are allogenic.
• Immunoglobulins are positively charged, so when they coat a cell or particle, they change the zeta potential so cells can bind and agglutinate.
• On re-exposure, the secondary response predominates and IgG antibodies are formed within 1-2 days
• Some IgM will be formed in the secondary response as well.
• The reaction between the antigens on RBCs and antibodies is called hemagglutination.
• Allogenic antigens are introduced to someone via transfusion or pregnancy, this is called sensitization or immunization.
• ABO antibodies; IgG, IgE, IgD are examples of affinity.
• There are 18 plasma proteins in complement.
• Not all cells are complement sensitive, but susceptible cells to complement include RBCs, WBCs, platelets, GNB.
• Complement proteins are destroyed by heat, they are labile proteins.
• Only IgG and IgM immunoglobulin types can activate complement.
• The secondary response is also known as the memory response or anamnestic memory.
• The major antibody produced in primary immune response is usually in low concentrations and is detectable in 3-4 weeks, this antibody is IgM.
• Antibodies made in response to foreign blood products may be IgG or IgM.
• Carbohydrates and lipoproteins act as antigens in transfusion situations.
• Ab are important in blood banking as the body's antibodies will bind to antigens on transfused RBC surfaces if it is recognized as foreign.