This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
[{'content': 'Which of the following is caused by C1 inhibitor deficiency? \nSelect and explain. \nA. Hereditary angioneurotic edema, B. SLE, C. Severe recurrent pyogenic infection, D. Collagen vascular disease', 'role': 'user'}, {'content': 'Answer: A \nExplanation: C1 esterase inhibitor is the main regulator of the activation steps of the classical complement pathway, and its genetic deficiency results in unregulated activity of vasoactive mediators and is the cause of hereditary angioedema (HAE). Suspect the diagnosis in patients with a history of recurrent peripheral angioedema and abdominal pain. C3 deficiency is associated with severe recurrent pyogenic infection. Deficiency of C1 to C4 is associated with SLE. Ref: Textbook of microbiology by Ananthanarayanan edition 6, page 108', 'role': 'assistant'}]