What are the different classes of antibodies and where are they found?

The five classes of antibodies are IgG, IgM, IgA, IgD, and IgE, found in various body fluids and cells.

Antibodies, also known as immunoglobulins, are proteins produced by the immune system to fight off foreign substances like bacteria and viruses. They are categorised into five classes: IgG, IgM, IgA, IgD, and IgE, each with unique roles and locations in the body.

IgG is the most common type of antibody found in the blood and extracellular fluid, protecting the body from infection by binding to many kinds of pathogens, such as viruses, bacteria, and fungi. It's also the only antibody that can cross the placenta, providing passive immunity to the foetus.

IgM is the first antibody the immune system makes to fight a new infection. It's primarily found in the blood and lymph fluid. It's larger than IgG and its structure allows it to effectively kill bacteria. It also triggers the complement system, an immune response that kills pathogens by forming a membrane attack complex.

IgA is found in areas of the body such as the nose, breathing passages, digestive tract, ears, eyes, and vagina. It's also present in saliva, tears, and breast milk. It protects body surfaces that are exposed to foreign substances from outside the body.

IgD is mainly found on the surface of B cells, a type of white blood cell. It's crucial in initiating early stages of the immune response. Its exact function is not fully understood, but it's believed to play a role in allergic reactions and the regulation of other immune cells.

IgE is found in the lungs, skin, and mucous membranes. It plays a key role in allergic reactions by triggering histamine release from mast cells and basophils when it encounters an allergen. It also protects against parasitic infections.

In summary, each class of antibodies has a unique role and location in the body, contributing to the body's overall immune response. Understanding these classes and their functions is fundamental to understanding how our immune system protects us from various pathogens and foreign substances.