Physiology of IgA and IgA deficiency

Although secretory immunoglobulin A (IgA) is important in mucosal immunity, selective IgA deficiency is the most common primary immunodeficiency of hu mans. In most cases this defect is not associated with any illness. The rea sons for this are unknown, but other immunological compensations might prov ide sufficient or complete restitution. Alternatively, it is possible that IgA deficiency alone may not predispose to disease, but additional immunolo gical abnormalities might be present in symptomatic individuals. Some IgA-d eficient individuals have a reduced antibody response to immunizations (eve n with normal IgG and IgM levels) and others have deficient responses to ba cterial polysaccharides when IgG subclass levels are normal. The physiologi cal role of IgA. the frequency and causes of IgA deficiency, the diseases a ssociated with its absence, and current limited understanding of the pathog enesis of selective IgA deficiency will be reviewed.