Immunoglobulins, or antibodies, are glycoproteins made up of four polypeptide chains:
- Two identical heavy chains
- Two identical light chains
The variation between different antibodies lies mainly in the heavy chains, which determines the antibody’s specificity and class. The main classes of immunoglobulins include:
- IgG:
- The most abundant antibody in the body.
- Found throughout tissue spaces.
- Directed against a variety of antigens.
- Can cross the placenta, providing immunity to the fetus.
- Responsible for secondary immune responses (after the body has been exposed to the same pathogen before).
- IgM:
- A pentameric antibody (five antibody units joined together).
- Has 10 antigen-binding sites (not “para top,” but likely “paratope” referring to the part of the antibody that binds to an antigen).
- Responsible for the primary immune response to infection.
- IgA:
- A dimeric antibody (two antibody units joined together).
- Found in mucous membranes (respiratory, digestive tract, mouth, gut) and various bodily secretions like tears, sweat, saliva, etc.
- It is the main antibody in breast milk, providing immunity to infants.
- IgE:
- Involved in allergic reactions (e.g., asthma) and hypersensitivity responses.
- Responsible for triggering the release of histamine from mast cells.
- Plays a role in defense against parasites like roundworms and tapeworms.
- IgD:
- Has a lesser-known or less understood function.
- May be important for early life immune responses and might help with antigen trapping.
Types of Immunity
- Innate Immunity:
- The body’s initial, nonspecific defense mechanism against pathogens.
- Includes physical barriers like the skin, as well as immune cells like macrophages and neutrophils that recognize and attack foreign invaders.
- Acquired Immunity:
- Specific immunity developed after exposure to an antigen.
- Involves the activation of lymphocytes, including T-lymphocytes (cell-mediated immunity) and B-lymphocytes (humoral immunity).
Humoral vs. Cell-Mediated Immunity
- Humoral Immunity: Involves B-lymphocytes and the production of antibodies (immunoglobulins) to neutralize pathogens or toxins.
- Cell-Mediated Immunity: Involves T-lymphocytes (T-cells) that directly attack infected or cancerous cells and coordinate other aspects of the immune response.
Leukocytes (White Blood Cells)
- White blood cells that include lymphocytes (T-cells, B-cells) and other immune cells like neutrophils, monocytes, etc.
- Natural Killer Cells (NK cells): Part of the innate immune system and can directly kill infected or abnormal cells.