Shedding of gangliosides from calf thymocytes.

In the course of our work on calf thymus gangliosides [Dyatlovitskaya, Zablotskaya, Azizov & Bergelson (1980) Eur. J. Biochem. 110, 475-483] we studied the gangliosides exfoliated from the cell surface of thymocytes. It was shown that calf thymocytes shed gangliosides both in vivo and in vitro. Various gangliosides were found to be present in high amounts both in extracellular plasma membrane vesicles and in the 64000 X g supernatant. The extracellular membrane fragments were comparatively higher in disialosyllactosylceramide and the 64000 X g supernatant was higher in sialosyllactosylceramide than the cells. Comparison of the ganglioside composition of extracellular membrane fragments, thymocytes and lymphocytes led us to suggest that the shedding of gangliosides from the surface of thymocytes may be involved in the transformation of immunologically incompetent cortical thymocytes into immunocompetent virgin T-cells.

Gangliosides of calf thymus and of normal and leukemic bovine lymphocytes.

The gangliosides of calf thymus and of lymphocytes from blood, lymph nodes, lymph and spleen of normal and leukemic cows were investigated in an attempt to determine whether there exists a relation between the ganglioside composition and the maturity of the lymphocytes. With all normal peripheral lymphocytes studied the largely prevailing (up to 97%) ganglioside component was found to be N-glycoloylneuraminosyllactosylceramide. The ganglioside spectrum of calf thymus was much more complex and included at least six different components. By thin-layer chromatography, methylation analysis and neuraminidase treatment they were identified as N-glycoloylneuraminosyl and N-acetylneuraminosyl lactosylceramides, N-glycoloylneuraminosylneolactotetraosylceramide, di-(N-glycoloylneuraminosyl), di-(N-acetylneuraminosyl) lactosylceramides and N-glycoloylneuraminosyl-N-acetylneuraminosyllactosylceramide. The ganglioside spectra of leukemic peripheral lymphocytes were different from those of normal peripheral lymphocytes and resembled the ganglioside profile of the thymus. The data obtained indicate that, in the normal animal, the development of thymocytes into mature peripheral lymphocytes is accompanied by loss of disialosyl-gangliosides and sialosylneolactotetraosylceramide. It is concluded that both the structure and the composition of the lymphocyte ganglioside become more simple during maturation and ageing of the lymphocyte.

DNA polymerase activity of lymphocyte nuclei of cattle lymph in the normal state and in lympholeukemia.

A comparative study wad made of the DNA polymerase activity of lymphocyte nuclei of cattle lymph in the normal state and in lympholeukemia. No significant differences were found in the specific DNA polymerase activity of the nuclei of normal and leukemic lymphocytes, both in the absence and in the presence of exogenous "activated" DNAs. The DNA polymerase activity of both types of nuclei was a maximum at pH 7.8 and a Mg2+ concentration of 4--6 mM. The DNA polymerase activities of lymphocyte nuclei of the lymph of healthy and leukemic animals did not differ in sensitivity to the inhibiting action of actinomycin D and in thermal stability. It was concluded that in cattle lympholeukemia, there are no significant changes in the DNA polymerase system of lymph lymphocyte nuclei.