Chronic urticaria sera increase basophil CD203c surface expression

Chronic idiopathic urticaria with functional autoantibodies: 12 years on

It is now recognized that approximately one-third of patients with chronic idiopathic urticaria (CIU) have histamine-releasing autoantibodies directed against either the high-affinity IgE receptor or, less frequently, against IgE. However, there are several unsolved problems relating to the role of such autoantibodies in the disease. Additionally, it is not clear whether CIU with autoantibodies can be classified as an autoimmune disease. The detection of patients with autoantibodies also poses challenges. Firstly, the only in vivo method, the autologous serum skin test, is at best 80% sensitive and specific using in vitro basophil histamine release assays as the verum. Secondly, in vitro tests are only done in a small number of research laboratories, and are not widely commercially available, and thirdly, there is some divergence between results obtained by different methods (functional and immunoassays) used to detect patients with autoantibodies. The presence of autoantibodies may be important clinically in a small group of severely affected, treatment-resistant patients, where immunomodulatory treatments may be helpful.

Autoantibodies to the high-affinity IgE receptor in chronic urticaria: how important are they?

PURPOSE OF REVIEW

Eighty to 90% of patients with chronic urticaria have no specific external cause for their disease, which is therefore labeled 'chronic idiopathic urticaria'. We now know, however, that as many as 30-50% of patients have evidence of an autoantibody to the high-affinity receptor for IgE (FcepsilonRI), which may be pathogenic. The exact prevalence and role of these autoantibodies is still under investigation.

RECENT FINDINGS

The frequency of autoantibodies to FcepsilonRI in chronic urticaria has been estimated at 30-50%, but extensive epidemiological studies have not been done. Recent work has confirmed that autoantibodies to FcepsilonRI can be functional, meaning that they can cause histamine release from basophils in vitro. Evidence increasingly suggests that such autoantibodies are also functional in vivo, but conclusive evidence is still lacking. Approximately 50% of cases of urticaria still have no known cause, but recent studies have demonstrated that some of these patients may have intrinsic abnormalities of basophils or mast cells.

SUMMARY

The recent evidence that is discussed in this review helps to clarify the role of autoantibodies in some cases of urticaria, but also points towards other non-autoimmune mechanisms that might be pathogenic. Further investigation in these areas will help us to understand the cause of urticaria in cases that are still classified as 'idiopathic'.