Immunoglobulins, commonly referred to as antibodies, are classified into five distinct types: IgG, IgA, IgM, IgD, and IgE. Each type serves a specific function within the immune system.

Immunoglobulins are proteins synthesized by the immune system to combat foreign invaders such as bacteria, viruses, and toxins. They play a vital role in the body’s immune response, with each type of immunoglobulin having a unique function.

• IgG is the most prevalent antibody in the bloodstream, accounting for approximately $75\%$ to $80\%$ of all antibodies in the body. It is highly effective in neutralizing toxins, eliminating bacteria, and enhancing the process of phagocytosis. Notably, IgG can cross the placenta, thereby providing passive immunity to the fetus against infections.

• IgA is predominantly found in various body fluids, including saliva, tears, and mucus within the respiratory and gastrointestinal tracts. It is essential for protecting mucosal surfaces that are exposed to foreign substances. Additionally, IgA is present in colostrum—the first milk produced after childbirth—offering the newborn passive immunity.

• IgM is the first antibody produced in response to an infection. It is primarily located in the blood and lymphatic fluid and is larger in size compared to other antibodies. IgM functions as a collective force to eliminate pathogens, particularly excelling at killing bacteria and agglutinating cells.

• IgD is found in small quantities in the blood and primarily serves to signal B cells for activation. When an antigen binds to the IgD antibody on a B cell, it stimulates the B cell to proliferate and produce more specific antibodies to target the antigen.

• IgE is primarily associated with allergic reactions and mediates the symptoms of allergies. It triggers the release of histamine and other chemicals that lead to allergic responses. Moreover, IgE plays a crucial role in defending the body against parasitic infections.

In summary, each type of immunoglobulin has a distinct role within the immune system, ranging from neutralizing toxins and eradicating bacteria to initiating allergic reactions and providing passive immunity. Understanding the functions of these immunoglobulins is essential for grasping how our immune system protects us from various diseases and infections.