A 35-year-old man with prior tuberculosis exposure undergoes a tuberculin skin test. At 48 hours, a 12 mm indurated, erythematous nodule appears at the injection site. The effector cells primarily responsible for this reaction are:
- A Mast cells and basophils
- B CD4+ Th1 cells and macrophages ✓
- C Neutrophils and complement C5a
- D IgG-producing plasma cells
Correct answer: B. CD4+ Th1 cells and macrophages
Explanation
The tuberculin (Mantoux) test is the classic example of Type IV delayed-type hypersensitivity. Antigen-presenting cells activate CD4+ Th1 cells, which secrete IFN-γ, activating macrophages and causing induration. The 48-72 hour peak response is T-cell dependent. Options A, C, and D describe antibody or innate mechanisms not involved in DTH.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.