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  Director : CUMANO Ana (cumano@pasteur.fr)


  abstract

 

In the Unité du Développement des Lymphocytes we study the major events implicated in the establishment of a functional immune system: 1.Establishment of the hematopoietic system, during embryonic development; 2. Development and physiology of a sub-population of T cells, the gd T cells; 3.Ontogeny, repertoire analysis and physiology of regulatory T cells, involved in the homeostatic regulation of the immune system.



  report

cale

Generation of hematopoietic stem cells, in the mouse embryo. A. Cumano.

Hematopoietic stem cells (HSC) guaranty the production of blood cells throughout life. HSC are not generated in the hematopoietic organs but are produced exogenously.

The aorta develops from the intra-embryonic mesoderm, called the Splanchnopleura (Sp), the anlage of the mesonephros, mesentery, and gonads develop in this site after the 10th day of gestation and this region is then called AGM (Aorta, Gonads, Mesonephros).

We have previously established that hematopoietic precursors in the intra-embryonic mesoderm are the only ones capable of long-term reconstitution of the hematopoietic compartment of adult NK-deficient hosts. They can thus be called HSC. The yolk sac-derived precursors are unable of long-term engraftment of recipient mice. We identified surface markers that allowed the isolation of a population of multipotent hematopoietic precursors, in the AGM, represented at a frequency of one in three cells. We sorted these precursors and analyzed the pattern of expression of genes involved in hematopoietic differentiation. This analysis allowed us to postulate that HSC are generated in the sub-aortic mesenchymal patches.

B cell development in the absence of interleukine 7. P. Vieira and A. Cumano.

In the absence of interleukin 7 (IL-7), the numbers of T and B lymphocytes are ten fold reduced in the peripheral lymphoid organs. This chronic lymphopenia results in a massive activation of peripheral T and B cells. Our analysis showed that B lymphopoiesis is completely abrogated in the bone marrow of adult IL-7-/- mice starting at the 7th week of age, illustrating the essential role of IL-7 in bone marrow lymphopoiesis. This blockage explains the chronicity of the lymphopenic status in these mice. We showed that the majority of B lymphocytes in these mice were of fetal or neonatal origin. Fetal B cell production is therefore active and partially independent from interleukin 7.

TLR4 gene expression during B cell ontogeny. P. Vieira.

We showed that TLR4, a gene product involved in the innate response to bacterial products such as LPS, is monoallelic expressed in B cells from the stage of pre-B cells, and in bone marrow granulocytes. The pattern of expression resembles the inactivation of the X chromosome.

Physiology of gd T cells: allelic specific negative selection of I-IELs Vg1/Vd4-P. Pereira

In the intestinal epithelium, gd T cells are the major population of peripheral gd T cells and represent half of the intra-epithelial lymphocytes (I-IELs). Isolation of I-IELs is an easy procedure and it is therefore an ideal population to study TCRgd-ligand interactions in vivo in non-immunized mice. We showed that there is an allele-specific cellular selection involved in the different representation of Vg1+Vd4+ in B6 and B10 mice. This selective mechanism could be due to an expansion (positive selection) of Vg1+Vd4+ cells in B10 mice or to the deletion of this population in B6 mice. To distinguish between these two possibilities we studied the junctional diversity of the g and the d chains expressed in I-IELs in these two mouse strains. Our results show that there is a reduced junctional diversity in the Vg1-Jg4 chains expressed in B6 I-IELs. This result suggests that the majority of I-IELs Vg1+ Vd4+ in B6 are deleted.

Ontogeny and physiology of CD4+ regulatory T cells. A. Bandeira.

Regulatory T cells protect tissue and organ integrity. This was shown for peripheral tolerance to self-antigens and in the case of the regulation of immune responses against exogenous antigens and in tolerance to transplantation antigens.

Thymic epithelium (TE) is capable of inducing stable tolerance to several tissues By a mechanism dependent on CD4+ regulatory T cells. Our studies revealed a major event in the development of T lymphocytes, the generation, in the thymus, of the first regulatory T cells selected by high avidity interactions between TCR and its ligand presented by the TE. The analysis of the TCR repertoire of CD4+CD25+ thymic and peripheral T cells in the C57BL/6 mouse revealed a repertoire as diverse as that found in naive T cells. These results suggest that 1. the clone size of regulatory T cells is small; 2. these cells recognize a diverse repertoire of natural ligands. This analysis confirms the idea that CD4+ regulatory T cells do not belong to a distinct developmental pathway from that of conventional T cells.

Independent Attached Group. R. Girard

The knowledge of the first steps of interactions of LPS with cells of the immune system, or from other tissues, represents a major step for understanding several pleiotropic effects triggered by these amphiphilic molecules. We have shown previously that LPSs from many bacterial strains, and among others from Salmonella enterica and Bordetella pertussis, could induce at the surface of human and mouse bone marrow granulocytes the expression of receptors with high affinity for lipid A, identified as CD14. This induction phenomenon is under the control of a lps locus on mouse chromosome 4, and depends on the expression of the transmembrane protein TLR4. We showed that these two types of LPS can also induce on these granulocytes a down—regulation of TNF-receptor 2 (CD120b). This effect is also TLR4-dependent. These results are the object of a paper submitted for publication.

We also asked whether other Toll molecules can be involved in the recognition of different types of LPSs, with lipid structures distinct from those of the two LPSs mentioned above. We demonstrated that LPSs from Legionella and Rhizobium can induce the expression of CD14 by a TLR4-independent mechanism. TLR2, possibly in association with other TLRs, was involved in the responses to these LPSs.

Keywords: hematopoiesis, lymphocyte development, gd T cells, regulatory T cells, grafts



  publications

puce Publications of the unit on Pasteur's references database


  personnel

  Office staff Researchers Scientific trainees Other personnel
  VOUGNY Marie-Christine (mcvougny@pasteur.fr) CUMANO Ana, Inserm, IP (DR Inserm, chef de labo IP,cumano@pasteur.fr)

BANDEIRA Antonio, CNRS (DR,bandeira@pasteur.fr)

PEREIRA Pablo, IP (chef de labo,ppereira@pasteur.fr)

GIRARD Robert, Paris VII (maitre de conf,rgirard@pasteur.fr)

GOLUB Rachel, Paris VII (maitre de conf,rgolub@pasteur.fr)

VIEIRA Paulo, CNRS (chercheur associé,pvieira@pasteur.fr)

LAABI Yacine, post-doc

BERTRAND Julien, PhD student

DIAS Sheila, PhD student

GRIGORIADOU Kalliopi, PhD student (departure 7/2002)

ZUBER Julien, PhD student

PEREIRA Joao, PhD student

DA SILVA Jr Hamilton, PhD student

DUJARDIN Hélène, DEA student

BURLEN-DEFRANOUX Odile (ingénieur IP,oburlen@pasteur.fr)

BOUCONTET Laurent (tech sup labo IP,bouconte@pasteur.fr)

DARDENNE Pascal (ITA IP)

VOUGNY Marie-Christine (sec directionmcvougny@pasteur.fr)


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