Immunohistochemical studies of human tissues with antibody to factor Xa

Factor Xa is a serine proteinase which functions principally at coagulation cascades. Factor Xa-like immunoreactivity has been examined in several human organs. Antibodies to the Factor stained macrophages in some tissues examined, including microglia in the brain white matter. They also stained epithelial cells in the nose, bronchus and duodenum. Some brainstem neurons, such as those in the oculomotor nucleus, substantia nigra and pontine nucleus, were also positive for the Factor. As reported by others, these results suggest that factor Xa may have pleiotrophic functions. Furthermore, the prefential localization to epithelium in the nose and bronchus is interesting in view of the previous notion that several viruses targeting the respiratory tract require factor Xa-like cellular proteinases for their replication and spread.