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

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

3. 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

2. 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)