The significance of the presence of anti-IgA antibodies in individuals with an IgA deficiency

Abstract. Class specific anti-IgA (anti-α) antibodies were found in seven out of sixteen patients in whom serum IgA was not demonstrable by the Mancini method (sensitivity down to 0.02 mg/ml). Allotype specific anti-IgA [anti-A₂m(l)] antibodies were found in an eighth patient. The anti-IgA antibodies proved to be of the IgG class. In the eight patients with anti-IgA antibodies, the presence of these antibodies could not be ascribed to immunization by administration of blood products. Isoimmunization in pregnancy and absorption of colostral IgA or animal IgA were other possible causes of anti-IgA antibodies.–Using a combined IgA/anti-IgA radioimmunoassay very low IgA levels (0.00013-0.020 mg/ml) were demonstrable in patients without anti-IgA antibodies whose serum IgA levels could not be determined by the Mancini method.–IgA metabolism was studied in five IgA-deficient patients. In two patients the rate of degradation of ¹³²I-IgA almost equalled that in individuals with a normal serum IgA level. In three patients, however, the rate of degradation was greatly increased. In their sera, in contrast to the first two, class specific anti-a antibodies were demonstrated.–One of these patients showed an anaphylactic reaction immediately after intravenous injection of ^mI-IgA. Only this patient showed complement fixation by the IgA/anti-IgA complex and IgA stimulation of lymphocytes.–The presence of anti-IgA antibodies has some important practical implications for those patients who need blood products.