Review Question - QID 210741

A 3-year-old boy is brought to his pediatrician by his mother for a productive cough. His symptoms began approximately 3 days prior to presentation and have not improved. His mother also reports that he developed diarrhea recently and denies any sick contacts or recent travel. He has received all of his vaccinations. Medical history is significant for pneumonia and a lung abscess of staphylococcal origin, and osteomyelitis caused by Serratia marcescens. Physical examination demonstrates growth failure and dermatitis. Laboratory testing is remarkable for hypergammaglobulinemia and a non-hemolytic and normocytic anemia. Work-up of his productive cough reveals that it is pneumonia caused by Aspergillus fumigatus. Which of the following is most likely the immune system defect that will be found in this patient?