How Antibodies Work

How Antibodies Work

  • Antibodies (Immunoglobulins) (Igs) – proteins secreted by B cells or plasma cells (clone of B cell) in response to an antigen and are capable of binding to that antigen
  • Antibody Classes – There are 5 Ig classes that are similar in function but have slightly different roles
  1. IgM – found in B lymphocytes; agglutinates antigens
  2. IgA – found in mucus, saliva, tears, and breast milk; protects against pathogens in mucous membranes and provides passive immunity for infants
  3. IgD – found in B cells and functions as receptors
  4. IgG – main antibody of both primary and secondary response, found in blood plasma; crosses the placenta and provides passive immunity for infants; provides long term immunity following vaccinations or infections
  5. IgE – binds to mast cells and basophils; triggers the release of histamines and other chemicals that cause inflammation and allergic responses (these are the “troublemakers”)


  • Once an antibody binds to an antigen, it inactivates the antigen in several ways:


  1. Complement fixation – antibody binds to the antigen and causes lysis, chemotaxis to attract other leukocytes and opsonization


  1. Neutralization – the antibody binds to a site on the bacteria or virus that releases toxins (exotoxins) to block the harmful effects of the toxin


  1. Agglutination – antibody will bind to the cell and cause clumping (occurs in mismatched blood) so they are easily captured by phagocytes


2 types of Immunity:

  1. Active Immunity – immune response is triggered by one’s own body
  • Naturally acquired active immunity – results after a person contracts a disease or illness and recovers leaving behind antibodies and memory cells
  • Artificially acquired active immunity – results after receiving a vaccine; vaccine triggers the primary immune response leaving behind antibodies and memory cells for the second attack


  1. Passive Immunity – immune cells are acquired somewhere other than one’s own body


  • Naturally acquired passive immunity – occurs in infants that receive antibodies from the mother through the placenta in utero and in mother’s milk after birth
  • Artificially acquired passive immunity – injections of antibodies are received from another person or animal (often used to treat snake bites, spider bites, or tetany)