Kinetics in the regions around lymphatic sinuses caused by antigenetic stimulation.

In this experiment, we examined the structure and the cellular reaction in lymphatic sinuses and the surrounding regions caused by T-independent (LPS) and T-dependent (SRBC) antigens administration in rats and SMA mice (LPS high responder strain).Lymphatic sinuses are incompletely lined by smooth lymphatic endothelial cells, and a distinctive basement membrane is lacking. Reticulum cells form a loose meshwork not only the regions around the lymphatic sinuses but also in the lumen of the sinuses. On days 1 and 3 after intraperitoneal injections of either LPS or SRBC, the lymphatic sinuses were dilated, and many macrophages, which bear LPS antigens immunostained by IC6H or EO9, were found in and out of the marginal and trabecular sinuses. After the carbon solution was injected into footpad subcutis, carbon laden-macrophages were also found there in a few minutes. That is to say, antigens reached LN via lymphatics, and spreaded around lymphatic sinuses easily in short time. The structure of lymphatic sinuses allows easy passage of antigens in and out of the sinuses, and the meshwork of reticulum cells causes the stasis of lymphatic flow.We also found in lymph node (LN) that B-lymphocytes (B-lys), which have the same phenotypes as marginal zone B-lys (MZB), were induced by LPS injection. These B-lys infiltlated around marginal and trabecular lymphatic sinuses on days 1 and 3 after LPS injection. Moreover, plasmacytic B-lys and plasma cells were found in the same regions as the B-lys infiltlated preceding the formation of activated germinal centers (GC) in SMA mice. These findings suggested that the B-lys mature into plasma cells around the lymphatic sinuses independent of B-lys differentiation in GC. Although marginal zone (MZ) do not exist in LN anatomically, it is also suggested that the regions around marginal and trabecular lymphatic sinuses are functionally identical to MZ.