• Granuloma is defined as a circumscribed tiny lesion and it’s about 1 mm in diameter. Granuloma is derived from word granule means granule like lesion and oma suffix generally refers to tumour but here it refers to collection of macrophages.
• Granuloma is type 4 hypersensitivity reaction. It’s protective but sometimes leads to tissue destruction because of poorly digestible antigen.
• Macrophages and monocyte engulf the antigen and tries to destroy it since the antigen is poorly degradable these cells fail to destroy antigen and macrophages undergoes morphological changes and transform into epitheloid cells.
• As macrophages have failed to destroy antigen they present it to CD 4 T lymphocytes. Lymphocytes get activated and releases interleukin 1 and interleukin 2 that stimulate more T cells, interferon gamma activates macrophages.
• And also TNF alpha that promotes proliferation of fibroblasts and activates the endothelium to secrete prostaglandin and growth factors which stimulate fibroblast growth.
Composition of granuloma
• Epitheloid cells are nothing but modified macrophages these are elongated cells and have slipper shaped nucleus . Nuclear chromatin is vesicular and lightly stained and cytoplasm is abundant and pale staining with hazy outlines.
• Multinucleate giant cells formed by the fusion of adjacent epitheloid cells containing more than 20 nuclei. The nuclei may be arranged like horseshoe or ring or may be clustered at 2 poles ( langhans gaint cell seen in tuberculosis ) or may be present centrally ( foreign body giant cell seen in foreign body tissue reaction).
• lymphoid cells as response to cell mediated immunity to antigen lymphocytes are the integral composition of granuloma. In some granulomas presence of plasma cells is indicative of humoral immune response.
• Necrosis is a feature of some granulomataous conditions like TB.
• Fibrosis is a feature of healing formed by fibroblast at the periphery.
So, Granuloma is having epitheloid cells at centre with interspersed gaint cells , surrounded peripherally lymphocytes and healing by fibroblast. Granuloma is a microscopic finding and it indicates chronic inflammation.
Reference :- Harsh mohan