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Abstract Background Autoantibodies against C1-inhibitor (C1-INH-Ab) have a diagnostic value in acquired angioedema due to C1-inhibitor deficiency (C1-INH-AAE), even though antibodies can circulate in complexes, which can be undetectable by proven methods. Our aim was to measure C1-INH/C1-INH-Ab complexes (CAC) and investigate their connection to C1-INH-Ab and the changes in their titer over time. Results 19 patients were diagnosed with C1-INH-AAE in the Hungarian Angioedema Center of Reference and Excellence; 79% of them had an underlying disease. Samples were examined with a newly developed in-house complex ELISA method. Patients with high C1-INH-Ab titer had a CAC titer which did not exceed the normal level and the ones with high CAC titer had a C1-INH-Ab titer which did not exceed the normal level. In case of those patients who had C1-INH-Ab and CAC of the same type of immunoglobulin, the increasing titer of C1-INH-Ab went together with the decreasing level of CAC and vice versa. CAC titer was already increased before the diagnosis of the underlying disease. Conclusions Free circulating and complex antibodies are in a dynamically changing equilibrium. CAC measurements can help to predict the development of an underlying disease. The efficiency of the treatment for underlying disease can be monitored by the decreasing CAC titers. Our results show that the CAC can be of important additional information besides the complement panel examination in case of C1-INH-AAE. Measurement of CAC is recommended to be done parallelly with C1-INH-Ab, so as to detect both free and bound antibodies.

Background: Autoantibodies against C1-inhibitor (C1-INH-Ab) have a diagnostic value in acquired angioedema due to C1-inhibitor deficiency (C1-INH-AAE), even though antibodies can circulate in complexes, which can be undetectable by proven methods. Our aim was to measure C1-INH/C1-INH-Ab complexes (CAC) and investigate their connection to C1-INH-Ab and the changes in their titer over time. Results: 19 patients were diagnosed with C1-INH-AAE in the Hungarian Angioedema Center of Reference and Excellence; 79% of them had an underlying disease. Samples were examined with a newly developed in-house complex ELISA method. Patients with high C1-INH-Ab titer had a CAC titer which did not exceed the normal level and the ones with high CAC titer had a C1-INH-Ab titer which did not exceed the normal level. In case of those patients who had C1-INH-Ab and CAC of the same type of immunoglobulin, the increasing titer of C1-INH-Ab went together with the decreasing level of CAC and vice versa. CAC titer was already increased before the diagnosis of the underlying disease. Conclusions: Free circulating and complex antibodies are in a dynamically changing equilibrium. CAC measurements can help to predict the development of an underlying disease. The efficiency of the treatment for underlying disease can be monitored by the decreasing CAC titers. Our results show that the CAC can be of important additional information besides the complement panel examination in case of C1-INH-AAE. Measurement of CAC is recommended to be done parallelly with C1-INH-Ab, so as to detect both free and bound antibodies. [ABSTRACT FROM AUTHOR]

Acquired angioedema due to C1-inhibitor deficiency (C1-INH-AAE) is a rare disease, which often appears with hematological underlying diseases. It can be diagnosed by complement testing and its treatment consists of the management of the underlying disease and angioedema attacks.The patient (59 year-old male) who was taking angiotensin-converting-enzyme inhibitor, was referred to the Hungarian Angioedema Center of Reference and Excellence due to an upper airway edema which did not respond to conventional treatment and required tracheotomy. At our Center, C1-INH-AAE was diagnosed, and myeloma multiplex was found as an underlying disease. He have been followed up for the past 15 years.After the first treatment series (chemotherapy and stem cell transplantation), his complement parameters returned to normal, but 5 years later they started to deteriorate, and the angioedema attacks recurred. To avoid the recurrence of myeloma multiplex, and due to the frequent and serious angioedema attacks, the patient got another series of rituximab treatment. It resulted in the normalization of complement values, and he had no further angioedema attacks.Angiotensin-convertase-enzyme inhibitors can trigger C1-INH-AAE.The recurrence of the underlying disease or the angioedema attacks can be predicted by the regular follow up of the complement parameters. Thus, the treatment of the underlying disease can be started in time, before the onset of severe symptoms.

Acquired angioedema due to C1-inhibitor deficiency (C1–INH-AAE) is a rare disease that can be diagnosed via complement testing. It often accompanies lymphoproliferative underlying diseases. Our study aimed to examine if there is a connection between complement parameters and the clinical symptoms of C1–INH-AAE, and, in case of a known underlying disease, its activity. The other question is how a connection, if proven, could help in the development of the therapeutic strategy of C1–INH-AAE patients.In the past 30 years, out of the 3938 patients sent to the Angioedema Center with angioedema symptoms, we have diagnosed C1–INH-AAE in 19 cases. An underlying disease was diagnosed in 15 patients. Most often lymphoma (6/19 patients) and monoclonal gammopathy of undetermined significance (6/19 patients) were found.Angioedema specific long-term prophylaxis did not result in an improvement in neither the frequency of the attacks nor in the complement parameters.A connection has been found between the presence and activity of any underlying disease, the frequency of the angioedema attacks and the decreased level of proteins of the complement system. Decreasing complement parameters warn about the appearance or the worsening of the underlying disease. The treatment of the underlying disease brings improvement in the complement parameters.Rituximab treatment reduced the number of attacks or completely made them disappear, and we experienced positive changes in complement parameters. Complement parameters supported the long-term efficacy of rituximab treatment for C1–INH-AAE.The change in complement parameters predict the relapse of the underlying disease, and it is a good indicator for the prediction of angioedematous attacks. In C1–INH-AAE, it is essential to examine the patients for underlying diseases, and to regularly follow up the patient's complement parameters.