Immune proteasomes in the development of the rat immune system

Abstract

The dynamics of the expression of LMP7 and LMP2 proteasome subunits in embryonic and early postnatal development of rat spleen and liver is investigated in comparison with the dynamics of chymotrypsin-like and caspase-like proteasome activities and expression of MHC (major histocompatibility complex) class I molecules. The immune subunits LMP7 and LMP2 distribution in spleen and liver cells in the development process is also studied. A mutual for both organs tendency to the increase of the expression of both LMP7 subunit and LMP2 one on P21 (the 21st postnatal day) as compared to the embryonic period is discovered. However, the total proteasome level is shown to be constant. At definite development stages, the dynamics of immune subunits expression in the spleen and liver was different. In the spleen gradual enhancement of both immune subunits level being detected on P1, P18 and P21, in the liver gradual enhancement periods on E16 (the 16th embryonic day) and E18 changed to the stage of the shrink of immune subunits level on P5. This level did not reliably change till P18 and was augmented on P21. The alterations revealed were accompanied by chymotrypsin-like activity raise and caspase-like activity drop in spleen by P21 as compared with the embryonic period, which proves the enlargement of proteasome ability to form antigenic epitopes for MHC class I molecules. In the liver, both activities increased by P21 in comparison with the embryonic period. Such dynamics of caspase-like activity can be explained not only by the change of proteolytic constitutive and immune subunits, but also by additional regulatory mechanisms. Besides, it is discovered that the increment of immune subunits expression in the early spleen development is connected with the process of successive forming the white pulp by B- and T-lymphocytes enriched by immune subunits. In the liver, the growth of immune subunits level by P21 was accompanied by their expression expansion in hepatocytes, while their plunge by P5 may be related to the loss of liver function of a primary lymphoid organ of the immune system by this stage and disappearance of B-lymphocytes enriched by immune proteasomes in it. In the spleen and liver, MHC class I molecules were revealed at the periods of the raise of proteasome immune subunits level. On E21 , the liver was enriched by neuronal NO-synthase, its level decreased after birth and enhanced to P18. This fact indicates the possibility of the induction of the immune subunits LMP7 [character: see text] LMP2 expression in hepatocytes in signal way with neuronal NO-synthase participation. The results obtained prove that T-cell immune response with spleen participation as regards rat liver cells is possible starting with P19-P21 stage. First, at this period, white pulp T-area is formed in the spleen. Second, enhanced immune proteasomes and MHC class I molecules levels in hepatocytes can procure antigenic epitopes formation from foreign proteins and their delivery to cell surface for their subsequent presentation for cytotoxic T-lymphocytes.