Pathogenesis of hypofibrinogenemia in familial hemophagocytic lymphohistiocytosis.

In order to investigate the cause of hypofibrinogenemia in familial hemophagocytic lymphohistiocytosis (FHL), formalin-fixed and paraffin-embedded tissue sections of the spleen obtained at autopsy were examined by using immunohistochemical methods for the presence of fibrinogen antigens, and such antigens were detected in approximately 10% of the histiocytes in a diffuse staining pattern. This finding indicates uptake of fibrin and/or fibrinogen molecules by activated histiocytes and suggests that hypofibrinogenemia of FHL is caused by the direct action of activated histiocytes on factor X through Mac-1 receptors, subsequent activation of the common pathway of the coagulation protease cascade, and uptake of fibrin and/or fibrinogen molecules by such cells.