Which class of antibodies is the most abundant in the bloodstream?

The most abundant class of antibodies in the bloodstream is IgG. This class of antibodies plays a crucial role in the immune system by providing the majority of antibody-based immunity against invading pathogens. IgG makes up approximately 75-80% of the antibodies found in human serum.

One of the key functions of IgG is its ability to neutralize toxins and viruses, enhance phagocytosis through opsonization, and activate the complement system, which helps in the destruction of pathogens. Additionally, IgG is the only antibody class that can cross the placental barrier, providing passive immunity to the fetus.

The other classes of antibodies, such as IgA, IgM, and IgE, have important functions but are present in lower concentrations in the bloodstream compared to IgG. IgA is primarily found in mucosal areas and secretions, IgM is the first antibody produced in response to an infection, and IgE is associated with allergic reactions and responses to parasitic infections.