Which immune cell type is primarily responsible for the positive reaction observed in a PPD (purified protein derivative) skin test, indicating prior exposure to Mycobacterium tuberculosis?

✓ Correct Answer: Option D

The PPD skin test is a classic example of a Type IV (delayed-type) hypersensitivity reaction, which is primarily mediated by Helper T lymphocytes (CD4+ T cells), specifically Th1 cells, that recruit macrophages to the site.