An 8-year-old boy is brought to the emergency department for a 2-hour history of increasingly severe nausea and confusion. His temperature is 103.5 F (39.7 C). Blood pressure is 85/50. Leukocyte count is 24,000/μL. Physical examination shows a rash on his legs and feet that does not demonstrate reduced coloration when pressure is applied. Cervical lymphadenopathy is present. The patient has an older brother who had a similar condition at the age of 10. Deficiency of which of the following is the most likely explanations for these findings?
Adenosine deaminase
CD18/LFA-1 integrin
CD40 ligand
C8 complement protein
IL-2 receptor common gamma chain
