Visualization of CD4/CD8 T cell commitment.
A system to innocuously visualize T cell lineage commitment is described. Using a "knock-in" approach, we have generated mice expressing a beta-galactosidase reporter in place of CD4; expression of beta-galactosidase in these animals appears to be an accurate and early indicator of CD4 gene transcription. We have exploited this knock-in line to trace CD4/CD8 lineage commitment in the thymus, avoiding important pitfalls of past experimental approaches. Our results argue in favor of a selective model of thymocyte commitment, demonstrating a fundamentally symmetrical process: engagement of either class of major histocompatibility complex (MHC) molecule by a differentiating CD4(+)CD8(+) cell can give rise to T cell antigen receptor (TCR)hi thymocytes of either lineage. Key findings include (a) direct demonstration of a substantial number of CD4-committed, receptor/coreceptor-mismatched cells in MHC class II- deficient mice, a critical prediction of the selective model; (b) highly efficient rescue of such "mismatched" intermediates by forced expression of CD8 in a TCR transgenic line, and an explanation of why previous experiments of this nature were less successful-a major past criticism of the selective model; (c) direct demonstration of an analogous, though smaller, population of CD8-committed mismatched intermediates in class I-deficient animals. Finally, we found no evidence of a CD4 default pathway.
Chan
S
S
Institut de Génétique et de Biologie Moléculaire et Cellulaire (CNRS/INSERM/ULP), Strasbourg, 67404 Illkirch Cedex, France.
Correia-Neves
M
M
Dierich
A
A
Benoist
C
C
Mathis
D
D
D000818:Animals; D015703:Antigens, CD / Q000032:analysis / Q000235:genetics; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation; D019070:Cell Lineage / Q000235:genetics / Q000276:immunology; D002478:Cells, Cultured; D015536:Down-Regulation; D017930:Genes, Reporter; D006579:Heterozygote; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010641:Phenotype; D012333:RNA, Messenger / Q000032:analysis; D011995:Recombination, Genetic; D013950:Thymus Gland / Q000166:cytology*; D001613:beta 2-Microglobulin / Q000235:genetics / Q000378:metabolism; D001616:beta-Galactosidase / Q000032:analysis / Q000235:genetics
D015703:Antigens, CD; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D012333:RNA, Messenger; D001613:beta 2-Microglobulin; D001616:beta-Galactosidase