6)A 22-year-old man complains to his family physician of fatigue, night sweats, and a dry unproductive cough. Until the past few
months, he had apparently been in good health. Acomplete blood count (CBC) and differential blood count reveal that he is lymphopenic. X-ray examination reveals an interstitial pneumonia. Skin test reactions to a battery of materials are normal. Which of the
following should be the next step in evaluating this patient’s illness?

A. CH50 complement assay
B. chemotaxis assay
C. identification of the organism that is
causing the pneumonia
D. intracellular killing assay
E. nitroblue tetrazolium reduction assay