Selective binding of biotinylated albumin to the lymphoid microvasculature

Chemically modified albumin binds to the surface of microvascular endothelia lining the vessel wall in several tissues. In this paper, we report that following their biotinylation, ovalbumin (bioOVA) and bovine serum albumin (BSA) [biotinyated albumin (bioAlb)] showed heterogeneous binding to distinct vascular subsets in different lymphoid tissues. The binding of bioAlb could be demonstrated both by fluorescent and enzymohistochemical techniques. In the spleen, the reaction was restricted to the red pulp sinuses whereas the white pulp vessels (including the central arteriole) and the marginal sinus were negative for bioAlb binding. In lymph nodes, the strongest labeling was observed in the medullary sinuses. In the thymus, the most prominent labeling of capillaries was restricted to the corticomedullary area where it was found to be less intense compared with the splenic reaction. The splenic reactivity of bioAlb in the mouse was defined using antibodies against endothelial cell subsets in distinct vascular beds in the red pulp and marginal zone, respectively. The bioAlb-binding elements of the splenic red pulp sinus architecture corresponded to the display of hyaluronan receptor stabilin-2 and subset-specific marker IBL-9/2 while they differed from the expression pattern of both the complementary red pulp sinus subset and the marginal sinus-lining cells expressing MAdCAM-1 antigen, respectively. Similar red pulp sinus-restricted reactivity could be demonstrated in the human, rat, and guinea pig. The use of bioAlb may thus offer a reliable probe for the histological identification of select microvascular endothelia in lymphoid tissues.