Transcription of granzyme A and B genes is differentially regulated during lymphoid ontogeny.
During development, thymocytes express a number of genes typical for activated peripheral T lymphocytes, including granzymes. We have now analyzed by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry, and cytochemistry fetal liver cells and thymocytes at various developmental stages for the expression of granzyme A-G genes. At days 13-17 of gestation, only granzyme B but none of the other granzymes is expressed in fetal liver. In the most immature, Pgp-1+IL2R alpha-, thymocyte subpopulation mRNAs for granzymes A-C but not for granzymes D-G are detectable. Upon further differentiation via Pgp-1-IL-2R alpha + into more mature Pgp-1-IL-2R alpha- thymocytes the level of expression of granzymes A, B, and C gradually declines reaching its lowest level at the CD4+ 8+ double positive stage. In fetal thymic lobes depleted of lymphoid cells by treatment with deoxyguanosine, no transcripts for granzymes A, B, and C were found indicating that the PCR signals are derived exclusively from early precursor T/natural killer (NK) lineage cells rather than from residual stromal elements. In mature CD4+CD8- and CD4-CD8+ thymocytes, granzyme B mRNA is found at similar levels in both subsets whereas granzyme A mRNA is expressed selectively in the CD4-CD8+ subset. Enzymatic activity of granzyme A was only seen in a fraction of CD4-CD8+ thymocytes negative for heat stable antigen (HSA) but not in the more immature HSA+ fraction of CD4-CD8+ thymocytes. The data suggest that (a) granzyme B is a pro-thymocyte marker for all T/NK lineage cells; (b) granzyme A transcripts are associated with thymocytes with the potential to develop into the CD8+ lineage; and (c) granzyme A enzymatic activity is only expressed in the most mature CD4-CD8+ stage, suggesting that granzyme proteins are not involved in early stages of thymocyte development.
Max-Planck-Institute for Immunobiology, Freiburg, Germany.
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Ebnet
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Levelt
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Tran
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Eichmann
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Simon
D000818:Animals; D005260:Female; D018507:Gene Expression Regulation, Developmental; D053804:Granzymes; D008099:Liver / Q000196:embryology / Q000201:enzymology; D051379:Mice; D008807:Mice, Inbred BALB C; D009924:Organ Culture Techniques; D012697:Serine Endopeptidases / Q000235:genetics*; D016176:T-Lymphocyte Subsets; D013950:Thymus Gland / Q000166:cytology / Q000196:embryology / Q000201:enzymology*; D014158:Transcription, Genetic
D053804:Granzymes; C509214:Gzmb protein, mouse; D012697:Serine Endopeptidases