Why would there be no immune response to gangrene?

Gngrene: Gangrene comes from dead tissue damaged from lack of proper blood supply or injury. Secondary bacterial infection can form in the dead tissue. There would be a marked inflammatory response. The immune system would try to stop the bacterial invasion into the healthy tissue but likely would be overwhelmed by the bacteria & toxins. Surgery may be used to debride the dead tissue.

Infection: There is an immune reaction .Gangrene is an infection that severely affects blood flow, and tissue death. Once blood flow stops, there is tissue death, and necrosis.