PLE-3679

A 35-year-old man who immigrated to the United States 15 years ago and lived in a crowded resettlement camp before coming to the United States presents with a cough that has been bothering him for several weeks. He has also lost 10 pounds. A gamma interferon release blood test is positive. Which of the following factors is known to be most important in triggering the granulomatous reaction to wall off and contain the infection?