antibodies

Examples of antibodies in the following topics:

• Monoclonal Antibodies

  • Monoclonal antibodies are monospecific antibodies that recognize one specific epitope on a pathogen.
  • Monoclonal antibodies (mAb or moAb) are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell.
  • Monoclonal antibody therapy is the use of monoclonal antibodies (or mAb) to specifically bind to target cells or proteins.
  • This allows the transformation of murine antibodies in vitro into fully human antibodies.
  • Schematic diagram of an antibody and antigens.

• Antibodies: Classes and Affinity Maturation

  • Virtually any microbe can trigger an antibody response.
  • Several complex genetic mechanisms have evolved allowing vertebrate B cells to generate a diverse pool of antibodies from a relatively small number of antibody genes.
  • One of these domains, the variable domain, is present in the heavy and light chain of every antibody, but is differentiated in antibodies generated from distinct B cells.
  • Combining these genes with an assortment of genes for other antibody domains generates a large cavalry of antibodies (i.e., a high degree of variability).
  • Some point mutations result in the production of antibodies having a weaker interaction (low affinity) with their antigen than the original antibody, and some generate antibodies with a stronger interaction (high affinity).

• Structure and Function of Antibodies

  • The antibody recognizes a unique part of an antigen (foreign object).
  • Most antibodies exist as a monomer, in which they have a single "Y" shaped sub-unit, but some antibodies can exist as dimers (two subunits) or pentamers (five subunits).
  • There are five different isotypes of antibodies.
  • IgG: Has four different forms,  and provides the majority of antibody-based immunity against invading pathogens, because it is the best opsonin of any type of antibody.
  • Each antibody binds to a specific antigen; an interaction similar to a lock and key.

• Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)

  • Among these antibodies are some which attack the red blood cells in the fetal circulation.
  • Antibodies are produced when the body is exposed to an antigen foreign to the make-up of the body.
  • In other words, if a mother has anti-RhD (D being the major Rhesus antigen) IgG antibodies as a result of previously carrying a RhD-positive fetus, this antibody will only affect a fetus with RhD-positive blood.
  • On rare occasions, IgG antibodies are produced.
  • In contrast, Rhesus antibodies are generally not produced from exposure to environmental antigens.

• Active and Passive Humoral Immunity

  • The humoral immune response is the aspect of immunity that is mediated by secreted antibodies.
  • The humoral immune response (HIR) is the aspect of immunity that is mediated by secreted antibodies produced by B cells.
  • Secreted antibodies bind to antigens on the surfaces of invading pathogens, which flag them for destruction.
  • Passive immunity is the transfer of active humoral immunity in the form of ready-made antibodies from one individual to another.
  • IgG is passed through the placenta to the developing fetus, and is the only antibody isotype that can pass through the placenta.

• Types of Adaptive Immunity

  • Its name comes from the idea that blood is one of the humors of the body, because antibodies will provide passive or active immunity through circulation in the blood stream.
  • The B-cells then rapidly produce a large number of antibodies which circulate through the plasma of the body.
  • Antibodies to provide a number of functions in humoral immunity.
  • There are 6 different classes of antibodies that provide similar but different functions and interact with different cells in the immune system.
  • The overall functions of antibodies are to bind to pathogens to opsonize them, which makes it easier for phagocytic cells to bind and destroy the pathogen.

• Antigens and Antigen Receptors

  • Antigens are molecules that initiate the immune response and can be bound by antibodies.
  • In immunology, an antigen is a substance that evokes the production of one or more antibodies.
  • At the molecular level, an antigen is characterized by its ability to be "bound" at the antigen-binding site of an antibody.
  • Note also that antibodies tend to discriminate between the specific molecular structures presented on the surface of the antigen.
  • The distinct molecular surface features of an antigen capable of being bound by an antibody (a.k.a. antigenic determinant).

• Blood Groups and Blood Types

  • This will cause the immune system to make specific antibodies to a particular blood group antigen and form an immunological memory against that antigen.
  • There are four blood types that differ based on the antigen expressed by the red blood cell and by the type of associated antibody found in the plasma.
  • Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen.
  • Blood group B individuals have the B antigen on their surface of their RBCs, and blood serum containing IgM antibodies against the A antigen.
  • Rh positive individuals do not have the antibodies for the Rh factor, but can make them if exposed to Rh.

• Complete Antigens and Haptens

  • Once the body has generated antibodies to a hapten-carrier adduct, the small-molecule hapten may also be able to bind to the antibody, but it will usually not initiate an immune response; usually, only the hapten-carrier adduct, which is the completed antigen, can do this.
  • Sometimes the small-molecule hapten can even block immune response to the complete antigen by preventing the adduct from binding to the antibody, a process called hapten inhibition.
  • In this case, the hapten acts as the epitope for the antigen, which binds to the antibodies without causing a response.
  • If this happens with enough haptens, there will not be enough antibodies left to bind to the complete antigen, so the antibody response is then inhibited.

• Maturation of B Cells

  • B cell development occurs through several stages, each stage representing a change in the genome content at the antibody loci.
  • They do not produce antibodies until they become fully activated.
  • Most of such B cells differentiate into plasma cells that secrete antibodies into blood that bind the same epitope that elicited proliferation in the first place.
  • B cells are the cells of the immune system that make antibodies to invading pathogens like viruses.
  • They form memory cells that remember the same pathogen for faster antibody production in future infections.