RAPID DEVELOPMENT OF INFANTS POLYMERIC IgA IN THE SERUM OF INFANTS

Abstract

Three molecular forms of IgA, monomeric (mIgA), polymeric (pIgA), and secretory (sIgA) make up approximately 85,15, and 1% of the IgA in adult serum. IgA concentration in secretions (sIgA) increases with age more rapidly than serum IgA. To evaluate the development of the IgA system, we measured total IgA, pIgA, and sIgA in the serum of infants 3-54 weeks of age. PIgA was measured by an enzyme-linked immunoassay based on the binding of pIgA to solid phase free secretory component. Total IgA and sIgA were measured by immunofluorescent assays. PIgA measurements in 10 normal adults sera (13±4mg/dl or 7%±2 of the total IgA) were similar to those reported using assays based on prior separation of the IgA forms. The pIgA concentration in infants' sera ranged from 3.2 to 27.9mg/dl. They increased from ½ to full adult levels over the first year of life. The pIgA was 10 to 75% of the total IgA in the infants' sera. The proportion of pIgA decreased with age due to an increase in mIgA. SIgA concentration ranged from 0 to 5.3mg/dl (0 to 28.9% of the total IgA) and did not correlate with age. These studies suggest that the various forms of serum IgA develop from pathway which mature at different rates. This is in keeping with the predominance of pIgA in the serum of many lower animal species. Alternatively, the relative predominance of high molecular forms of IgA in infants' sera may be due to immaturity of the mechanisms for removal of these forms of IgA.