In Leishmania pathogenesis, which cells can activate infected macrophages?

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

Answer: (A)

Leishmania hides inside macrophages, so turning those cells into parasite killers is essential. The key signal that activates infected macrophages is IFN-γ, which pushes macrophages to a microbicidal state, producing nitric oxide and reactive species to kill the intracellular amastigotes. Natural killer cells provide an early source of IFN-γ in response to IL-12 from other immune cells, rapidly activating macrophages before a full Th1 response develops. This early activation helps control the infection, with Th1 cells later contributing more IFN-γ for sustained macrophage activation. Neutrophils and B cells don’t deliver this activating signal to macrophages in the same way.