Expression of MHC Antigents in Fetal Rat Thymus

Major histocompatibility complex (MHC)　Class I antigen is known distinct on cell surface of the mature cells including lymphocytes but not detected on early stage of thymocytes. Monoclonal antibody, OX-18 or HAM-2 is the specific antibody to rat MHC Class I antigen and OX-6 is that to MHC Class II. These antibodies are detected immunohistochemically or flow cytofluorometrically by using HRP or FITC conjugated anti-mouse immunoglobulin.　Main findings are as follows : MHC Class I antigen first appeared on thymic epithelial cells at day 15 of gestation and with the progress of fetal stage MHC Class I antigen positive cells appeared to increase in number and its intensity of the staining. MHC Class I antigen on thymocytes at about day 15 of gestation was negative, however at day 19 of gestation was about 36%, which is same as in normal young adult thymus. The degree of total antigen amount expressed in fetal thymus was compared with that in adult thymus, using radioactive binding inhibition assay. The amount of antigen is quite low at days 18 and 20 of gestation compared to that of adult. From these findings it is suspected that MHC Class I antigen first appeared on epithelial cells and a few days later on thymocytes. Thus, the interaction between MHC Class I positive epithelial cells and thymocytes may be important for the differentiation and maturation of thymocytes.

HMC antigen

fetal thymus

Monoclonal antibodies

Thymic epithelial cells