An 18-year-old girl comes to the physician for a 3-day history of low-grade fever, dry cough, and mild wheezing. She has been treated for several bacterial pneumonias since childhood and occasional sinusitis. Vitals are: temperature 100 F, RR 16, HR 74, BP 120/80. She has a history of atopic dermatitis. Her older brother has autoimmune gastritis. Which of the following best describes the deficient immunologic species in this patient?
A) Binds complement
B) Component of B cell receptor
C) Highest affinity
D) Highest avidity
E) Secreted as dimer with J-chain via transcytosis
