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

Presence of epithelioid cell granuloma, Langhans giant cells and lymphocytes is characteristic of chronic granulomatous inflammation Chronic granulomatous inflammation occurs when two conditions are satisfied i.e. a. 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) b. When macrophages have successfully phagocytosed the injurious agent but it survives inside them. Some important definitions- • Epithelioid cells - These are activated macrophages They are large cells with abundant pale foamy cytoplasm Epithelioid cell granuloma An epitheloid cell granuloma is an aggregate of these activated macrophages. Granulomas are usually surrounded by lymphocytes, plasma cells fibroblast and collagen. Langhans giant cells It is a typical feature of epithelioid cell granuloma. These are formed by the fusion of macrophages and characterized by 10-50 nuclei around the periphery.