Different expression of the recombination activity gene RAG-1 in various populations of thymocytes, peripheral T cells and gut thymus-independent intraepithelial lymphocytes suggests two pathways of T cell receptor rearrangement.
The presence of transcripts of the recombination activating gene RAG-1 was studied by in situ hybridization on selected populations of murine thymocytes, peripheral lymphocytes and gut intraepithelial lymphocytes (IEL), obtained by cell sorting. RAG-1 mRNA was found in a majority of "double-positive" (DP) thymocytes, but was absent in "single-positive" thymocytes and peripheral T lymphocytes. The only other T lineages in which about 10%-20% of the cells contained RAG-1 mRNA, and in smaller amounts, were "double-negative" (DN), T cell receptor (TcR) gamma delta- cortical thymocytes and gut CD3- IEL. These observations suggest that (a) the high expression of RAG-1 transcripts in DP thymocytes is related to the process of expansion-selection of these cells, probably accompanied by repeated TcR rearrangements, and that (b) in contrast, CD3- IEL from the gut (which are thymus independent) as well as some DN thymocytes undergo limited TcR rearrangement giving rise locally to TcR+ T cells without prior extensive process of local expansion-selection. A small percentage of peripheral B cells also contained RAG-1 mRNA, raising the possibility that this protein may also be involved in immunoglobulin class switching.
Guy-Grand
D
D
INSERM U.132, Hôpital Necker-Enfants Malades, Paris, France.
Vanden Broecke
C
C
Briottet
C
C
Malassis-Seris
M
M
Selz
F
F
Vassalli
P
P
D000818:Animals; D015870:Gene Expression; D015329:Gene Rearrangement, T-Lymphocyte; D016654:Genes, RAG-1; D018398:Homeodomain Proteins; D007422:Intestines / Q000166:cytology / Q000276:immunology; D051379:Mice; D008815:Mice, Inbred Strains; D009693:Nucleic Acid Hybridization; D011506:Proteins / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D011995:Recombination, Genetic; D013601:T-Lymphocytes / Q000166:cytology / Q000502:physiology*; D013950:Thymus Gland / Q000166:cytology
D018398:Homeodomain Proteins; D011506:Proteins; D012333:RNA, Messenger; C064658:RAG-1 protein