Question | Answer |
IgM | The first antibody produced in response to an antigen. Fixes complement. Does not cross the placenta. |
IgG | The primary antibody in the secondary response (second-exposure). Opsonizes (coats) bacteria, fixes complement, thereby destroying the bacteria. Crosses the placenta. |
IgA | Found in mucosal secretions (upper respiratory tract, genitourinary tract). Engages pathogens outside the body. Aggregated form activates the alternative pathway of complement activation only. |
IgE | Mediates Type I hypersensitivity reaction by binding to antigens and the surface of mast cells and basophils, stimulating the release of histamine. Levels often elevated in helminth infections. |
IgD | Membrane IgD is part of the functional B cell receptor on mature B cells. |
Type I hypersensitivity reaction | Results from IgE-mediated release of inflammatory molecules such as histamine from mast cells and basophils, can manifest as an asthma attack, a local wheal-and-flare, or anaphylaxis. |
Type 2 hypersensitivity reaction | Antibody and complement mediated, is cytotoxic in nature and occurs in autoimmune hemolytic anemia, Graves' disease, and myasthenia gravis. |
Type 3 hypersensitivity reaction | Caused by immune complex deposition and subsequent complement activation, may be a complication of IV administration of antigenic medications (penicillin). |
Type 4 hypersensitivity reaction | Cell mediated, results in a delayed (24 to 48 hour) response. It is mediated by T cells. Examples include transplant rejection, TB skin test, and contact dermatitis (poison ivy). |
Tc cells (cytotoxic cells) | Executors of the cell-mediated arm of the acquired immune system. |
Th cells (T-helper cells) | Coordinators of the acquired immune system. They decide whether to attack an invader with a predominantly cell-mediated or humoral (antibody-mediated) attack. |
Th1 cells | Stimulate the cell-mediated arm of the acquired immune system by secreting IL-2 and λ-interferon, which stimulate the action of macrophages and Tc cells. |
Th2 cells | Stimulate the humoral (antibody-mediated) arm of the acquired immune system by secreting IL-4 and IL-5, which stimulate B cells to make antibodies. |