Albumin and fibrinogen, two independent plasma proteins are able to produce a relatively stable complex which is present on the surface of multiple cells. Existence of such structure was reported in the 1960s and 1970s by Brzosko and Nowosławski, Groniowski, and confirmed in vitro by Lipiński in 1995. It was believed to provide protection against immunocompetent cells. In 2002, we showed the presence of a structural lining composed of albumin and fibrinogen on the surface of placental villi. Immunohistochemistry and immunoflurescence confirmed presence of this complex on the endothelial surface. We also found complement proteins such as C1q, C4d, C9, and double immunofluorescence confirmed the presence of this complex and complement components in the aortic vasa vasorum. Both membrane-bound (CD46, CD55, CD59) and soluble (H factor) complement inhibitors were present.
Studies indicate that this lining is composed of plasma proteins and complement components and since it is present on the endothelial surface, it can play a role of a natural immune barrier protecting against pathological processes in the blood vessels.