Granuloma?is an?inflammation?found in many diseases. It is a collection of?immune cells?known as?histiocytes?(macrophages).?Granulomas form when the?immune system?attempts to wall off substances it perceives as foreign but is unable to eliminate. Such substances include?infectious organisms?including?bacteria?and?fungi, as well as other materials such as?keratin?and?suture?fragments.
肉芽腫是一種常見(jiàn)的炎性反應(yīng)，由組織球細(xì)胞（巨噬細(xì)胞）聚集而成。當(dāng)免疫系統(tǒng)無(wú)法清除體內(nèi)的異物時(shí)，便會(huì)形成肉芽腫來(lái)阻隔。異物包括細(xì)菌、真菌等微生物，和角化物、縫合碎片等。
Macrophages?(specifically?histiocytes) are the cells that define a granuloma. They often, but not invariably, fuse to form multinucleated giant cells (Langhans giant cell).?The macrophages in granulomas are often referred to as "epithelioid". This term refers to the vague resemblance of these macrophages to?epithelial cells. Epithelioid macrophages differ from ordinary macrophages in that they have elongated nuclei that often resemble the sole of a slipper or shoe. They also have larger nuclei than ordinary macrophages and their cytoplasm is typically more pink when stained with?eosin. These changes are thought to be a consequence of "activation" of the macrophage by the offending antigen.
The other key term in the above definition is the word "organized" that refers to a tight, ball-like formation. The macrophages in these formations are typically so tightly clustered that the borders of individual cells are difficult to appreciate. Loosely dispersed macrophages are not considered to be granulomas.
All granulomas, regardless of cause, may contain additional cells and?matrix. These include?lymphocytes,?neutrophils,?eosinophils,?multinucleated giant cells,?fibroblasts?and?collagen?(fibrosis). The additional cells are sometimes a clue to the cause of the granuloma. For example, granulomas with numerous eosinophils may be a clue to?coccidioidomycosis?or allergic?bronchopulmonary?fungal disease, and granulomas with numerous neutrophils suggest?blastomycosis,?granulomatosis with polyangiitis,?aspiration pneumonia?or?cat-scratch disease.
