Immunoglobulin A (IgA): The Guardian of Mucosal Immunity

Structure and Forms

IgA is one of the five main classes of antibodies that are found in the human body and there are two major types of IgA, namely the secretory IgA (sIgA) and the serum IgA. The basic unit of it is made of two heavy chains and two light chains and it has the shape of a “Y” like the other immunoglobulins. However, IgA has the capacity to be dimer and even higher polymers especially in its secretory form. Secretory IgA is further subdivided into two categories namely the J chain which serves in connecting two IgA molecules and the secretory component which acts in shielding the antibody from being hydrolysed in the harsh mucosal environments. There are two types of IgA in human being, IgA1 and IgA2, which differ in their structure and the distribution in the tissues. The majority of IgA1 is found in the blood while IgA2 is more abundant in the secretions of the mucosal surfaces indicating their specific function in the various body folds.

Production and Distribution

IgA is the most abundantly produced immunoglobulin in the body, with daily production exceeding that of all other antibody classes combined. The majority of IgA is synthesized by plasma cells located in mucosal tissues, particularly in the gastrointestinal tract, respiratory system, and genitourinary tract. These plasma cells are derived from B lymphocytes that have undergone class switching in response to various signals, including cytokines and T cell help. The production of secretory IgA involves a complex process where dimeric IgA is transported across epithelial cells via the polymeric immunoglobulin receptor (pIgR). During this transport, the secretory component is added, resulting in the complete sIgA molecule. The distribution of IgA varies significantly across body fluids and tissues, with high concentrations found in mucosal secretions, breast milk, and to a lesser extent, in serum.

Functions in Immune Defence

IgA is the most important antibody which is present in the mucosal surfaces as the first layer of protection. The main function of IgA is immune exclusion, where it acts as a barrier to prevent adhesion and penetration of pathogens and antigens through the mucosal epithelium. Some of the functions that are carried out include agglutination of microorganisms, neutralization of toxins and interference with microbial motility. Secretory IgA is also involved in the control and regulation of the microbial flora and in establishing the symbiosis with the microorganisms that are beneficial to the host. IgA is the only immunoglobulin that can be secreted into the serum, and when it is there, it can bring about some immune reactions such as complement-dependent inflammation, although this role is not as important as other immunoglobulins. Furthermore, IgA is also essential in maternal infant transmission of immunity where it is transmitted through breast milk to protect the newborn while their own immune system is still developing.

Clinical Significance and Disorders

IgA deficiency is the commonest of the primary immunodeficiency disorders affecting 1 in 500 people of European descent. Although most people with this disorder have no problems at all, some may develop repeated respiratory and gastrointestinal infections, allergies, and autoimmune diseases. On the other hand, increased levels of IgA has been found to be linked with certain diseases such as IgA nephropathy which is the most common type of glomerulonephritis. IgA immune complexes are trapped in the kidneys thereby causing inflammation and may result in kidney failure. IgA is also used in celiac disease where anti-tissue transglutaminase IgA antibodies are used as markers. IgA has been found to be important in mucosal immunity thus making it a focus in vaccine development especially for pathogens that infect through mucosal routes.

Therapeutic Applications and Future Perspectives

New mucosal vaccines that design for inducing IgA is being created with an aim of IgA-based enhancing therapeutics the involve protection the against generation respiratory of and monoclonal gastrointestinal antibodies infections. The role of IgA in cancer immunotherapy considered, is but also mainly being for cancers that affect the mucosal surfaces. Future research may also focus on enhancing the knowledge on the part played by IgA in the regulation of microbiota and the creation of new strategies for the design of mucosal vaccines as well as the identification of new therapeutic targets in autoimmune diseases and cancer. Also, in the future, the technological progress in the biotechnology field will help to create more stable and efficient IgA-based therapeutics to solve the problems appeared during the development of the molecule with the complex structure and high sensitivity to proteolysis.

It is imperative to note that the role of IgA in mucosal immunity is crucial since it offers protection against a huge number of potential invaders while at the same time promoting harmony with the friendly flora.

Suitable ELISA Kits

• Immunoglobulin A ELISA Kit
• IgA ELISA Kit