The analysis of lymphoid cell differention by using cell lines transformed with a ts mutant of Abelson murine leukemia viurs.

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We have succeeded in obtaining a ts mutant of Abelson murine leukemia viurs(A-MuLV) through a biologikal assay relying on changes in the differentiation state of B lymphomas at permissive and nonpermissive temperatures.The viral activity was further analysed by bone marrow colony assay, focus assay,and gene transfection assay using proviral DNA of ts virrus. The results confiem that the virus carries theproperty of a ts mutat virus.By using this ts mutant,designated as ts-49,we have established several immature B lymphomas to analyse the mechanism of immunoglobulin(Ig) expression during differentiation. We observed 2)the usage of a VH gene to join toa D@j segment was predetemined prior to the Ig rearrangement,2) u chains, synthesized at the stage of pre-B cells,were expressd on the cell surface as an associated from with unknown molecule(s).It is not known whether the phenomena are only peculiar to established lymphomas,however,the analysis provides new information about the programming of Ig gene expression,in contrast to the esteblished view that VH genes are rendomely selected and used for VDJ joining at the stage of Ig gene rearrangement.On the other hand,we have established a new system to transform lymphoid cells in fetal thymus by transforming viruses including a ts mutant.By using this new system,we observed that B precursors were stored at high frequency in fetal thymus.Fetal thymus carries activity. to store B precursors of fetal liver origin and to support the generation and survivals of pre-B lymphomas of thymic and fetal liver origin.This result leads new insight about the role of thymic stromas on B cell development.In addition,we have establishd immature T cell lines;one is "double negative",CD3+,and]positive cell and antogher is Thy-1+,AA4.1+, IL2R+.The latter may belong toimmature T lineage cells which are nou known in the literature.