Human IgG anti-IgA that reacts with purified IgA1 and IgA2 subclasses is known as “class-specific” anti-IgA. This type of anti-IgA in recipients has been associated with very severe complement-mediated anaphylaxis when they are transfused with components containing plasma. An earlier theory that anaphylaxis was mediated by IgE anti-IgA antibodies has been refuted by research data
To prevent anaphylaxis, patients with high-titer IgG class specific anti-IgA antibodies must receive either components in which plasma has been removed (such as Saline Washed Red Blood Cells or Frozen-Deglycerolized Red Blood Cells) or plasma-containing products (such as FFP and Apheresis Platelets) from IgA-deficient (IgA-D) donors. The American Red Cross maintains a registry of rare donors including IgA-D donors.
Anti-IgA antibodies that only react with either IgA1 or IgA2 are termed "limited specificity." These antibodies have been implicated in ATRs but the reactions are less severe.
Both IgG and IgE antibodies to haptoglobin have been associated with anaphylactic reactions; seven such reactions were observed in Japan. As with anti-IgA, patients with anti-haptoglobin antibodies must receive components in which plasma has been removed (such as Saline Washed Red Blood Cells or Frozen-Deglycerolized Red Blood Cells).
It has also been hypothesized that food allergies may result in ATRs and at least one case of anaphylaxis has been reported from the passive administration of peanut allergen to a recipient with the corresponding food allergy. Reactions to food allergens appear to be less frequent and less severe, although the etiology of these reactions is difficult to determine.