Thy-1 antigen on rat bone marrow cells: immunochemical and fine morphological studies.

Immunochemical and fine morphological studies were conducted to clarify molecular characteristics of Thy-1 antigen on rat bone marrow cells and cell types expressing Thy-1 in rat bone marrow. For this purpose, a xenoantiserum highly specific for Thy-1 was prepared by immunizing rabbits with partially purified Thy-1 glycoprotein from rat brains. This antiserum reacted with approximately 90% of thymocytes, 10% of spleen cells, 30% of bone marrow cells and less than 2% of lymph node cells in normal rats, and the similar reactivity of this serum was also observed with spleen, lymph node and bone marrow cells obtained from congenitally athymic (rnu/rnu) rats. The anti-Thy-1 serum used in this study, as well as anti-asialo GM1, showed cytotoxic effect on natural killer (NK) cells in rats, suggesting that the NK cells, unlike those cells in mice, express both Thy-1 and asialo GM1. Immunoelectron microscopic observation performed on Thy-1 positive rat bone marrow cells showed that Thy-1 was expressed on immature cells ancestral to erythrocytes or granulocytes and on possible pluripotent hemopoietic stem cells as well as on bone marrow lymphocytes. It seems likely that an inverse relationship exists between Thy-1 expression and maturation of rat bone marrow cells including erythrocytic, granulocytic and lymphocytic cell series. Thy-1 antigen defined by our antiserum on rat bone marrow cells appears to be a sialoglycoprotein with 24 K molecular weight, which could be labeled by periodate-tritiated borohydride. The same antiserum precipitated a 27 K molecular weight sialoglycoprotein from rat thymocytes, which was regarded as the same molecular species as the 24 K molecular weight glycoprotein on rat bone marrow cells on the basis of data obtained from absorption studies.