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 macropha ges and histiocytes. Thus, besides clot retraction, a possible role of FXIIIa has also been postulated in inflammation. In order to test thi s hypothesis, FXIIIa-expression in granulomatous lesions due to sarcoi dosis and mycobacterial infection was investigated. In the 12 cases (s ix 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 devoi d of these cells. We did not find any difference in the distribution o f FXIIIa-positive cells in both conditions; thus FXIIIa did not improv e the differential diagnosis between sarcoidosis and tuberculosis. How ever, FXIIIa-producing macrophages seemed to contribute to the centrip etal fibrosis in granuloma. These results further suggest that the bas ic pathogenetic mechanisms in granuloma formation are very similar, re gardless of their origin from sarcoidosis or tuberculosis.