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Published May 1, 1997 | public
Journal Article

Different Developmental Arrest Points in RAG-2 -/- and SCID Thymocytes on Two Genetic Backgrounds Developmental Choices and Cell Death Mechanisms before TCR Gene Rearrangement

Abstract

To analyze the early development of T cell precursors in the absence of TCR gene rearrangement, recombinase-activating gene-deficient (RAG-2 -/-) thymocytes were compared with thymocytes from SCID mice on the C.B-17 (BALB) and B6 genetic backgrounds. RAG-2 -/- thymocytes accumulate as quiescent cells with a heat-stable Ag (HSA)-positive CD25+ CD44- c-kit(low) phenotype, resembling normal cells just before selection for functional TCR beta-chain expression. CD44 and c-kit progressively down-regulate in the HSA+ subset, providing a background-independent and TCR-independent developmental clock. On this basis, compared with RAG-2 -/- thymocytes, SCID thymocytes 1) arrest at more heterogeneous, and generally earlier, stages; 2) accumulate to lower overall cell numbers; and 3) maintain higher populations of cycling and activated G1 cells, showing both increased responsiveness and increased cell death. B6-SCID thymocytes appear to die particularly early. Low levels of Fas were observed on "advanced" HSA+ SCID thymocytes but not on any RAG-2 -/- thymocytes, suggesting a potential difference in activation state or mechanism of death. In both RAG-2 -/- and SCID thymocytes, there are also two discrete subsets of HSA(low) CD25- CD44+ c-kit+ cells: a Sca-1+ CD44++ CD122- NK1.1- putative progenitor subset and an NK-like Sca-1- CD44+(+) CD122+ NK1.1+ subset. The absolute cell numbers in these HSA(low) subsets and the extent of NK cell differentiation, measured by perforin expression, are nearly constant in all the mutant strains analyzed, in contrast to the HSA+ CD25+ population, which was expanded in the RAG-2 -/-. Thus, the SCID thymocytes appear to undergo a normal generation but a premature death as compared with the RAG-2 -/- thymocytes.

Additional Information

© 1997 American Association of Immunologists. Received for publication November 12, 1996. Accepted for publication January 24, 1997. This work was supported by U.S. Public Health Service Grants Al34041 and AG 13108, by the State of California Tobacco-Related Disease Research Program, and by the Stowers Institute for Medical Research. H.W. is a scientist of the Stowers Institute for Medical Research. The Caltech Flow Cytometry/Cell Sorting Facility and Biopolymer Synthesis Facility were aided by subsidies from the Beckman Institute. We thank Drs. Yoichi Shinkai and Fred Alt, Harvard Medical School, Boston, MA, for providing the original RAG-2 -/- mice, and Dr. Ken Dorshkind, University of California, Riverside, CA, who initially provided us with C.B-17-SCJD mice, which were in each case the founders of our colonies. We are also indebted to Patrick Koen, whose expert help contributed greatly to the flow cytometry in this work, and to Robin Monson Condie, Heidi Sikonia, and Raymond Hotz, whose dedicated care of the immunodeficient mice over the past two years made all these studies possible. We gratefully acknowledge the Caltech Biopolymer Synthesis Facility for oligonucleotides and the Caltech Flow Cytometry and Cell Sorting Facility, in which most of the work presented here was done. Finally, we express our gratitude particularly to Professor Shigekatsu Tsuji, Department of Physiology, Wakayama Medical College, Wakayama, Japan, for his gracious support of K. Owada-Makabe throughout her participation in this work.

Additional details

Created:
August 19, 2023
Modified:
October 24, 2023