A 40 year old man has chronic cough with fever for several months. The chest radiograph reveals a diffuse reticulondular pattern. Microscopically on transbronchial biopsy there are focal areas of inflammation containing epitheloid cell granuloma, Langhans giant cells, and lymphocytes. These findings are typical for which of the following type of hypersensitivity immunologic responses:

Ans. is 'd' i.e. Type IV Presence of epitheloid cell granuloma, Langhans giant cells and lymphocytes is characteristic of chronic granulomatous inflammationChronic granulomatous inflammation occurs when two conditions are satisfied i.e.When an active T lymphocyte-mediated cellular immune response occurs.Lymphokines produced by activated T lymphocytes inhibit migration of macrophages and cause them to aggregate in the area of injury and form granulomas.This pathological process is characteristic of Type IV hypersensitivity (so one can say that- Type IV hypersensitivity is essential for chronic granulomatous inflammation)When macrophages have successfully phagocytosed the injurious agent but it survives inside them.Some important definitions- * Epitheloid cells - These are activated macrophagesThey are large cells with abundant pale foamy cytoplasmEpitheloid cell granulomaAn epitheloid cell granuloma is an aggregate of these activated macrophages.Granulomas are usually surrounded by lymphocytes, plasma cells fibroblast and collagen.Langhans giant cellsIt is a typical feature of epitheloid cell granuloma. These are formed by fusion of macrophages and characterized by 10-50 nuclei around the periphery.