Granulomatous inflammation is a characteristic feature of Type IV hypersensitivity reaction against tubercle bacilli. When ceain non degradable antigen such as tubercle antigen is present, the initial perivascular mononuclear cell monocyte infiltrate is replaced by macrophages over a period of 2-3 weeks. The accumulated macrophage then undergo morphological transformation into epithelial like cells and are then referred to as epithelioid cells. A microscopic aggregation of epithelioid cells, usually surrounded by a collar of lymphocytes, is referred to as granuloma. And this pattern of inflammation is called granulomatous inflammation.Ref: Robbins Pathologic Basis of Disease, 6th Edition, Pages 204-6