[9] Deficiency of C1-inhibitor permits plasma kallikrein activation, which leads to the production of the vasoactive peptide bradykinin.

In addition to the episodes of facial swelling and/or abdominal pain, it also predisposes to autoimmune diseases, most markedly lupus erythematosus, due to its consumptive effect on complement factors 3 and 4.

[18] It is a highly purified, pasteurized and nanofiltered plasma-derived C1 esterase inhibitor product; it has been approved for routine prophylaxis against angioedema attacks in adolescent and adult patients with HAE.

[19] A recombinant C1-inhibitor obtained from the milk of transgenic rabbits, conestat alfa (brand name Ruconest), is approved for the treatment of acute HAE attacks in adults.

It is also possible to produce it by recombinant technology, but Escherichia coli (the most commonly used organism for this purpose) lacks the eukaryotic ability to glycosylate proteins; as C1-inhibitor is particularly heavily glycosylated, this sialylated recombinant form would have a short circulatory life (the carbohydrates are not relevant to the inhibitor function).

[24] This form of recombinant C1-inhibitor also has been given orphan drug status for delayed graft function following organ transplantation and for capillary leakage syndrome.