Immunodeficiencies Quiz: Ace Your Exams

A 2-year-old boy is brought to his primary care physician’s office for evaluation of recurrent pulmonary infections and failure to thrive. Since birth, the parents report the patient has had two episodes of pneumococcal pneumonia and five episodes of otitis media. He recently recovered from a diarrheal illness caused by Cryptosporidium parvum. His vaccinations are up to date, and he does not take any medications. Family history is significant for similar symptoms in the patient’s brother, who died from pneumococcal pneumonia last year. Temperature is 37.2 C (99 F), pulse is 80/min, respirations are 20/min and blood pressure is 90/55 mmHg. Physical examination reveals a child who is small for his age. Laboratory results are shown below.

 

Laboratory value	Result
Complete blood count
Hemoglobin	12  g/dL
Leukocyte count	10,100 /mm3
Platelet count	200,000/mm3
Immunoglobulins
IgG	250 mg/dL
IgA	24 mg/dL
IgM	700 mg/dL
IgE	undetectable
CD4/CD8 ratio	2 (normal, 1-4)

This patient’s condition is most likely caused by a failure of which of the following processes?