What happens when there is defective Th1 responses or a Th2-dominant response?

• A. Tuberculoid leprosy due to strong macrophage activation
• B. Lepromatous leprosy due to poor macrophage activation from weak Th1 response
• C. Autoimmune disease due to Th2 skewing
• D. Severe viral infections due to lack of Th17

Answer: (B)

This question tests how the balance between Th1 and Th2 responses affects macrophage activation and control of intracellular pathogens. A strong Th1 response drives IFN-γ–mediated activation of macrophages, enabling them to kill intracellular bacteria. If the Th1 response is weak or if a Th2-dominant pattern prevails, macrophage activation is insufficient, allowing widespread intracellular infection to persist.

That’s why the scenario described aligns with lepromatous leprosy: poor macrophage activation due to a weak Th1 response (or a Th2-skewed response) leads to extensive bacterial proliferation and disseminated disease. By contrast, a robust Th1 response would produce tuberculoid leprosy, with strong macrophage activation and limited bacteria. The other options don’t fit because Th17 isn’t the main driver for viral defense in this context, and Th2 skewing is not typically associated with autoimmune disease as the primary outcome here.