Copyright © 2000 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Intrathymic injection of the Abelson murine leukemia virus (A-MuLV) results in transformation of immature T and B lymphoid cells. In this report we demonstrate that the concentration of A-MuLV injected into murine thymi influences the selection of the transformation target. Thus, concentrated A-MuLV gives rise to Thy-1⁺ B220^- thymomas. In contrast, dilute virus induces B220⁺ thymomas that also express low levels of Thy- 1 (Thy-1^lo), a phenotype that is similar to marrow-derived progenitor B-lymphoid cells (pro-B cells) that are highly susceptible to A-MuLV transformation invitro. However, rare B220⁺ lymphoid cells isolated from normal adult thymi were not transformed by A-MuLV invitro, while B220⁺ cells isolated from bone marrow were highly susceptible to transformation by A-MuLV. The Thy-1^lo B220⁺population in the primary thymomas had not rearranged TCRγ, TCRβ, or Igκ genes, but contained subpopulations that assembled Ig DJ_H or VDJ_H genes and were therefore similar to transformed pro- and pre-B cells obtained from A-MuLV infected fetal liver and adult bone marrow, respectively. However, unlike A-MuLV-transformed pro- and pre-B cells, many (40– 70%) of the Thy-1^lo B220⁺ transformed thymoma cells had not rearranged Igh genes, and therefore appear to represent undifferentiated lymphoid cells. We conclude that A-MuLV may transform an undifferentiated lymphoid target in the thymus.