Immunohistochemical detection of coagulation factor XIIIa in postmortem human brain tissue.

Blood coagulation factor XIII is responsible for stabilizing fibrin clots by catalyzing the formation of covalent bonds between lysine amino groups and glutamine carboxyl groups. A smaller form of factor XIII called factor XIIIa (FXIIIa) occurs intracellularly in platelets, monocytes and peripheral macrophages. Using a specific antibody to FXIIIa, we detected this molecule immunohistochemically in a subpopulation of reactive microglia and macrophages in a number of neurological disease states. These included Alzheimer's disease and other degenerative disorders. FXIIIa was also detected in capillaries and some leukocytes in both control and neurologically diseased tissue. FXIIIa is known to cross-link a variety of proteins in addition to fibrin. Its occurrence in some reactive microglia suggests a possible role in the fundamental pathology.