Factor XIIIa expression in granulomatous lesions due to sarcoidosis or mycobacterial infection

The a-subunit of the clotting factor XIII (FXIIIa) has previously been shown to be synthesized by cells of monocyte lineage such as macrophages and histiocytes. Thus, besides clot retraction, a possible role of FXIIIa has also been postulated in inflammation. In order to test this hypothesis, FXIIIa-expression in granulomatous lesions due to sarcoidosis and mycobacterial infection was investigated. In the 12 cases (six cases each) examined, FXIIIa-positive macrophages were consistently detected by immunohistochemistry. They were predominantly observed in the periphery of granulomas, whereas the centers were generally devoid of these cells. We did not find any difference in the distribution of FXIIIa-positive cells in both conditions; thus FXIIIa did not improve the differential diagnosis between sarcoidosis and tuberculosis. However, FXIIIa-producing macrophages seemed to contribute to the centripetal fibrosis in granuloma. These results further suggest that the basic pathogenetic mechanisms in granuloma formation are very similar, regardless of their origin from sarcoidosis or tuberculosis.