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Published October 1, 1993 | public
Journal Article

Functional and phenotypic analysis of thymocytes in SCID mice. Evidence for functional response transitions before and after the SCID arrest point

Abstract

Thymocytes from severe combined immune deficient (SCID) mice undergo developmental arrest at an early stage, before most TCR gene rearrangement. They therefore represent a natural test case to assess those aspects of T cell development that are TCR independent. Multiparameter flow cytometry was used to analyze the array of immature phenotypes present in the SCID thymus at steady state, as defined by the markers CD4, CD5, Sca-1, NK1.1, CD44, heat-stable antigen (HSA), and IL-2R alpha. The results suggest a simple developmental block in SCID mice rather than a program of aberrant differentiation. SCID thymocytes displayed efficient, developmentally regulated functional responses. Approximately 20-25% of the cells, mostly within the IL-2R alpha +HSA+CD44low fraction, could be induced to express IL-2. This IL-2 inducibility was highly dependent on IL-1 costimulation, in agreement with the behavior of normal immature thymocytes. These results formally demonstrate that competence to express IL-2 is developed independently of TCR expression or gene rearrangement. Comparison of the response properties of various SCID thymocyte subsets indicated that IL-2 inducibility is first likely to be acquired at an early (Sca-1++CD44++HSAlow) stage. A later functional transition was revealed by comparing patterns of IL-2R alpha regulation in normal and SCID IL-2R alpha +HSA+CD44low thymocytes. The SCID thymocytes uniformly maintained IL-2R alpha expression on in vitro stimulation, whereas only a minority of the normal cells in the corresponding subset could do so unless IL-1 was also added. The SCID arrest point thus appears to separate the IL-2R alpha +HSA+CD44low stage into distinct early (TCR independent) and late phases. Normal cells that progress beyond the SCID arrest point appear to lose, rather than gain, competence to make various responses, even before they leave the IL-2R alpha +HSA+CD44low stage. A model is proposed in which discrete changes in functional competence define novel transitions in early thymocyte development, at least some of which may be linked to TCR-beta gene rearrangement before positive or negative selection.

Additional Information

© 1993 American Association of Immunologists. Received for publication January 4, 1993. Accepted for publication June 20, 1993. This research was supported by US. Public Health Service Grant AI 19752. The Caltech Flow Cytometry/Cell Sorting Facility was supported by funds from the Lucille P. Markey Charitable Trust, the Beckman Institute at Caltech, and a U.S. Public Health Service Cancer Center Core Grant CA 32911. D. C. gratefully acknowledges partial support from a Gordon Ross Memorial Fellowship, and from the Markey Trust Program in Developmental Biology at Caltech. We thank Robin Monson Condie and Steven I. Shen for painstaking and excellent care of the SCID mouse colony, Ken Dorshkind for SCID breeders, Patrick Koen for expert help with flow cytometry, Richard Chizzonite for an initial gift of anti-IL-1 receptor antibody, Ueli Gubler for the murine IL-la cDNA clone, and PharMingen, Inc. for test samples of valuable derivatized antibodies. We are particularly grateful to Drs. Eric Davidson and Laura Lebow for thoughtful and detailed criticism of early drafts of the manuscript, and to two anonymous referees and our colleagues, Paul Boyer, Julia Yang-Snyder, and Lisa Scherer for many useful critical suggestions. We also thank Stephanie Canada, Renee Thorf, and Cathy Blagg for valuable assistance in preparing the manuscript.

Additional details

Created:
August 20, 2023
Modified:
October 24, 2023