Biological Activities of IgA

Immunoglobulin (Ig) A is by far the most abundantly produced Ig in the human body, yet its physiological functions and pathological impact are incompletely understood. In part this is because IgA is the most structurally heterogeneous form of Ig, occurring in multiple molecular forms and subclasses, which are differentially distributed between two largely separate physiological compartments: the systemic circulation and tissues and the mucosal surfaces and their associated secretions. Secretory (S) IgA has evolved as the predominant mucosal Ig in mammals and birds. SIgA possesses a variety of functional properties capable of protecting the body against all types of pathogens and serving also to maintain mutualism with the commensal microbiota. Its mechanisms of protection are distinct from those of other Ig isotypes and are largely noninflammatory in nature. However, derangements in its production or arising from exploitation by microbes can lead to pathological consequences.