In Leishmania pathogenesis, parasite infection may promote inefficient activation of which cells?

• A. TH2 cells
• B. TH1 cells
• C. B cells
• D. NK cells

Answer: (B)

The key idea is that protection against Leishmania relies on a strong cell-mediated, Th1-driven response. Th1 cells secrete IFN-γ, which activates macrophages to kill intracellular amastigotes. Leishmania infection often shifts the immune response toward a Th2 profile or otherwise dampens Th1 activation, so the activation of Th1 cells becomes inefficient. With insufficient Th1 activity and IFN-γ production, macrophages aren’t properly activated to control the intracellular parasite, allowing the infection to persist and disease to develop.

Th2 cells, by contrast, promote antibody responses which are not effective against intracellular pathogens like Leishmania. B cells produce antibodies that have limited access to parasites inside macrophages, so their role isn’t central to clearing this infection. NK cells can provide early IFN-γ, but the sustained, protective response specifically hinges on Th1 activation of macrophages, which is precisely the process that Leishmania tends to impair.