Antibodies are crucial in our immune system as they serve as effector molecules that aid in mediating fluid immunity. These immunoglobulins are produced by plasma cells, which are differentiated and proliferated by B cells in response to antigens. The antibodies, specifically IgG and IgM, are specialized molecules that bind specifically to the corresponding antigen. Ig stands for immunoglobulin and refers to a class of proteins that includes antibodies. IgG and IgM are two different types of immunoglobulins that differ in several ways.
The concentration of immunoglobulins in vivo varies depending on the fluid compartment. In serum and extracellular fluid, IgG is the most abundant, making up approximately 75% to 80% of total serum Ig. On the other hand, IgM only accounts for 5% to 10% of the total serum Ig.
The synthesis of IgG begins around 3 months after birth, and by the age of 3-5, it reaches levels close to that of adults. This antibody is widely distributed throughout the body and possesses a high affinity. During the secondary immune response, IgG is the primary antibody produced. On the other hand, IgM is synthesized and secreted at an earlier stage in ontogeny. It has the ability to activate complement more easily than IgG. Even during late embryonic development, the fetus can produce IgM.
Both IgG and IgM have distinct clinical significance. IgG is the sole immunoglobulin capable of crossing the placenta, thereby transferring to trophoblast cells and entering the fetal bloodstream. This plays a crucial role in protecting neonates against infections. On the other hand, IgM is the earliest antibody in the initial humoral immune response. Detecting pathogen-specific IgM in serum indicates recent infection, allowing for early diagnosis. An increase in IgM levels in umbilical cord blood suggests intrauterine infection, such as rubella virus or cytomegalovirus. The differential implications of IgG and IgM provide valuable insights into fetal health and infection diagnosis.
