Claude Penit

Naive T cells proliferate strongly in neonatal mice in response to self-peptide/self-MHC complexes

Adult naive T cells, which are at rest in normal conditions, proliferate strongly when transferred to lymphopenic hosts. In neonates, the first mature thymocytes to migrate to the periphery reach a compartment devoid of preexisting T cells. We have extensively analyzed the proliferation rate and phenotype of peripheral T cells from normal C57BL/6 and T cell antigen receptor transgenic mice as a function of age. We show that, like adult naive T cells transferred to lymphopenic mice, neonatal naive T cells proliferate strongly. By using bone-marrow transfer and thymic-graft models, we demonstrate that the proliferation of the first thymic emigrants reaching the periphery requires T cell antigen receptor-self-peptide/self-MHC interactions and is regulated by the size of the peripheral T cell pool.

Kinetics of Lymphocyte Proliferation during Primary Immune Response in Macaques Infected with Pathogenic Simian Immunodeficiency Virus SIVmac251: Preliminary Report of the Effect of Early Antiviral Therapy

ABSTRACT The aim of this study was to evaluate the kinetics of lymphocyte proliferation during primary infection of macaques with pathogenic simian immunodeficiency virus (SIV) and to study the impact of short-term postexposure highly active antiretroviral therapy (HAART) prophylaxis. Twelve macaques were infected by intravenous route with SIVmac251 and given treatment for 28 days starting 4 h postexposure. Group 1 received a placebo, and groups 2 and 3 received combinations of zidovudine (AZT), lamivudine (3TC), and indinavir. Macaques in group 2 received AZT (4.5 mg/kg of body weight), 3TC (2.5 mg/kg), and indinavir (20 mg/kg) twice per day by the oral route whereas macaques in group 3 were given AZT (4.5 mg/kg) and 3TC (2.5 mg/kg) subcutaneously twice per day, to improve the pharmacokinetic action of these drugs, and a higher dose of indinavir (60 mg/kg). The kinetics of lymphocyte proliferation were analyzed by monitoring 5-bromo-2′-deoxyuridine (BrdU) uptake ex vivo and by fluorescence-activated cell sorting analysis. HAART did not protect against SIV infection but did strongly impact on virus loads: viremia was delayed and lowered during antiviral therapy in group 2, with better control after treatment was stopped, and in group 3, viremia was maintained at lower levels during treatment, with virus even undetectable in the blood of some macaques, but there was no evidence of improved control of the virus after treatment. We provide direct evidence that dividing NK cells are detected earlier than dividing T cells in the blood (mostly in CD45RA− T cells), mirroring plasma viremia. Dividing CD8+ T cells were detected earlier than dividing CD4+ T cells, and the highest percentages of proliferating T cells coincided with the first evidence of partial control of peak viremia and with an increase in the percentage of circulating gamma interferon-positive CD8+ T cells. The level of cell proliferation in the blood during SIV primary infection was clearly associated with viral replication levels because the inhibition of viral replication by postexposure HAART strongly reduced lymphocyte proliferation. The results and conclusions in this study are based on experiments in a small numbers of animals and are thus preliminary.

Terminal deoxynucleotidyl transferase in acute lymphoblastic leukemias and chronic T cell proliferations

Abstract Cells from patients with acute lymphoblastic leukemias (ALL) (28 cases), T-derived chronic lymphocytic leukemias (CLL) (6 cases), Sezary syndrome (3 cases) and thymomas (3 cases) were studied for both immunological membrane phenotype and terminal deoxynucleotidyl transferase (TdT) content (using chromatography of cell extracts on phosphocellulose). Cells from 25 cases of ALL contained TdT. T-derived ALL had relatively homogenous TdT values whereas a wider range of TdT activity was found in non-T non-B ALL. Cells from 3 ALL cases had no detectable enzyme; two were B-derived ALL, one T-derived ALL. Cells from the three thymomas and from one case each of Sezary syndrome and T-CLL had TdT activity. The significance of TdT in neoplastic disorders is discussed in the light of the known distribution of TdT in various subpopulations of normal mature T-cells and T-cell precursors.

Developmental changes in terminal deoxynucleotidyl transferase of the chicken thymus.

Abstract Terminal deoxynucleotidyl transferase activity begins to be detectable in the thymus of 14-day old chicken embryos. It reaches a maximum 3 weeks after hatching, and persits at a fairly high level in 21-weeks old chickens. Multiple chromatographic forms of TdT are detected, and the relative proportions of these forms change during the development of the chicken.

Effect of “facteur thymique sérique” (FTS) on TdT expression in murine thymocytes

Abstract Normal murine thymocytes were incubated in the presence of FTS (facteur thymique serique) or of retinoic acid. FTS induced a partial decrease of TdT activity (measured by a biochemical assay) and of the percentage of TdT-positive cells (measured by an immunofluorescent assay). This action was rapid (a plateau was reached after 2 hr) and specific (no inhibition of α DNA polymerase was observed, and vasopressin has no effect). Double immunofluorescence labeling experiments using Thy 1.2 and TdT antibodies showed that the targets of FTS action comprised mainly cortical thymocytes which were transformed into Thy 1.2+, TdT- cells. Retinoic acid also induced a decrease of TdT activity, but this effect needed a longer time than FTS. Murine lymphoma cells were also studied in this system, but a decrease in TdT activity was only obtained with retinoic acid.

Ribonuclease-sensitive DNA polymerase activity associated with particles distinct from A type and C type viral particles in murine myeloma tumor cells

Murine myeloma tumor cells in culture produce intracisternal, A-type, virus-like particles, as well as C-type particles [l-3]. Wilson and Kuff [4] have shown that A-type particles contain an enzymatic activity responsible for the polymerization of dTMP in the presence of the synthetic hybrid poly rA*oligo dT, but they did not find any endo~~no~s ~bonuclea~sensitive DNA polymerase activity similar to that of oncornaviruses [S-S], In this paper we report studies on two DNA pdymerase activities present in particulate extracts of mym the other is responsible for the poly rA*oligo dT-directed dTMP polymerization. In order to characte~ze the particles bearing the endogenous activity and to compare them with virus-like particles, fractionation experiments of the MF cell extracts were carried out. In addition, the two DNA polymerase activities were studied in extracts from MF cell-induced solid mice tumors, which produce mostly A-type particles, and in extracts of an epithelioid cell variant (referred to as ME cells, [9, 101) which produces neither Anor Cstype particles.

Purification and Properties of Chick Terminal Deoxynucleotidyl Transferase (TdT)

The thymus is made up of two anatomical parts: the stroma, containing the epithelium, and the thymocytes which belong to the lymphoid series of the hematopoietic cells. The embryonic origins of these two populations are different: the thymocytes derive from stem cells which colonize the thymic rudiment (which is initially purely epithelial). This facts were suggested by Moore and Owen (1) and the timing of the lymphoid colonization of the embryonic thymus was established by Le Douarin and Jotereau (2) using a technique based on the production of interspecific chimeras. Such chimeras are obtained by grafting the thymic rudiments of chick embryos in the somatopleure of quail embryos (or vice-versa). Quail cells are easily distinguished from chick cells using the Feulgen-Rossenbeck staining of chromatin: the quail chromatin is condensed in a large mass in the center of the nucleus whereas the chick chromatin is finely dispersed (3). By an appropriate choice of the respective ages of the grafted rudiments and of the host embryos, it could be shown that the epithelial thymus is colonized by stem cells during two receptive periods : from 6 1/2 days to 8 days and from 12 to 13 days.