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C Penit

Publications and source records attributed to C Penit.

At least 37 records · Page 2Linked to original sources
PubMed1988

In vivo dynamics of CD4-8- thymocytes. Proliferation, renewal and differentiation of different cell subsets studied by DNA biosynthetic labeling and surface antigen detection.

The proliferative status of CD4-8- thymocyte subsets was determined by in vivo or in vitro labeling with bromodeoxyuridine (BrdUrd), a nonreutilized thymidine analogue detectable with a monoclonal antibody, simultaneously with relevant surface proteins. An actively cycling subset [J11d+, interleukin 2 receptor-positive (IL 2R+)] was defined, besides a relatively resting one (J11d-, Pgp1+, T cell receptor-positive). Continuous per os administration of BrdUrd showed that 85% only of CD4-8- thymocytes were labeled in 6 days confirming the existence of a relatively long-term resting subset. By contrast, CD4+8+ thymocytes were all labeled in 3-4 days. Observation of labeled CD4-8- cells after pulse labeling showed an immediate decrease of their absolute number per thymus, confirming their low autorenewal capacity. However, a small number of labeled cells which were hydroxyurea or colchicine resistant remained CD4-8- for several days and progressively acquired surface expression of IL 2R. IL 2R expression by cycling CD4-8- cells during thymus regeneration after antimitogenic drug treatment was rapid, but very transient. According to these results most CD4-8- thymocytes appear as largely engaged in a proliferation-dependent differentiative process, and do not behave as true stem cells. Consequently, this subset is principally renewed by thymic immigration of exogenously produced resting cells. However, a tenfold expansion of CD4-8- cells was found in the fetal and regenerating thymus, suggesting two proliferative phases during intrathymic CD4-8- cell maturation, the first one yielding to cell expansion and the second to cell differentiation. A tentative evaluation of daily cell immigration is proposed starting with the determination of the number of cells beginning DNA synthesis each day. A global model is finally discussed by confronting our kinetic results with the known reconstitution capacities of CD4-8- thymocyte subsets.

Animals↗
PubMed1988

Localization and phenotype of cycling and post-cycling murine thymocytes studied by simultaneous detection of bromodeoxyuridine and surface antigens.

Bromodeoxyuridine (BrdUrd) was incorporated in vivo or in vitro into the DNA of proliferating murine thymocytes. Surface antigens Thy1, Lyt2 (CD8), L3T4 (CD4), interleukin-2 receptor (IL2-R), and the V beta 8 chain of the T-cell receptor were detected using specific monoclonal antibodies with the biotin-avidin system, and cells were then treated for DNA denaturation. Simultaneous detection of BrdUrd and surface markers was performed on cell smears and frozen sections by double-color immunofluorescence. The phenotype of cycling cells, determined in fetal thymus and in the thymus of mice from birth to one year of age, showed relative stability after the initial growth period, despite severe involution of the gland. Phenotypic evolution of cycling cells and their progeny was also studied in colchicine-treated animals and was shown to reproduce sequential events of T-cell differentiation. On sections, the highest frequency of cycling cells was observed in the outer cortex in normal thymus, but the first cells to start proliferation during regeneration were mostly located in the deep cortex and corticomedullary junction. These results show the high potential of this method, as compared to autoradiography of radiolabeled cells.

Animals↗
PubMed1987

Control of prothymocyte proliferation by thymic accessory cells.

All thymocyte subpopulations derive from intrathymic precursors which are double negative (DN) for Lyt-2 and L3T4 differentiation antigens. Although nearly half of DN cells express a receptor for interleukin 2 (IL 2R), they respond poorly to IL 2. DN cell proliferation can be obtained in the presence of various exogenous stimuli, but the in vivo signal for DN cell response to IL 2 remains unclear. We show in the present report that phagocytic cells of the thymic reticulum are able to induce the proliferation of DN thymocytes in the presence of recombinant IL 2 (rIL 2). Cell-to-cell contact is needed for this effect. Antibodies directed against class I MHC antigens but not against class II can inhibit DN cell proliferation. DNA-synthetizing cells were labeled by incubation with 10 microM bromodeoxyuridine either before or at various times during the culture period. Bromodeoxyuridine was then detected in the DNA of proliferating cells and/or their progeny already stained with anti-Lyt-2 and L3T4 antibodies. During the initial 16 h and independently of culture conditions, 16-25% of the cells expressed surface antigens and 50-65% of them derived from DN cells which were in S phase just before culture; these differentiated cells had a very short life span. In the second culture period, the presence of both rIL 2 and thymic accessory cells was necessary for cell survival. In these conditions, DN cell number and proliferation rate were constant and a low number of Lyt-2+ and/or L3T4+ cells was continuously generated. Thymic accessory cells therefore appear to provide the signal(s) necessary for IL 2-induced proliferation of thymocyte precursors. Implications of these findings for normal in vivo intrathymic proliferation and differentiation are discussed.

Animals↗
PubMed1986

In vivo thymocyte maturation. BUdR labeling of cycling thymocytes and phenotypic analysis of their progeny support the single lineage model.

Spontaneously cycling thymocytes have been labeled in vitro and in vivo by bromodeoxyuridine (BUdR), a non-reutilized precursor of DNA that is detectable by a monoclonal antibody. Studies of BUdR-labeled cells have included the determination of their anatomical location, size, and nuclear aspects and of their cell surface phenotype. Dividing blasts were initially located in the cortex (mainly but not exclusively in the subcapsular region) and expressed the double-negative (Lyt-2- L3T4-) and double-positive (Lyt-2+ L3T4+) phenotypes. The fate of these cells have been determined in days after BUdR administration, and we observed an initial double-negative to double-positive transition that was followed by the death of the majority of labeled cells in the cortex. As of day 3, the few surviving cells acquired a mature helper phenotype (Lyt-2- L3T4+) and began migrating into the thymic medulla. The exclusive medullary location of blast cell progeny was observed between days 5 and 10 post-BUdR administration. These results suggest a direct precursor-product relationship between dividing cortical cells and mature medullary thymocytes, and therefore support the single lineage model of intrathymic differentiation.

Animals↗
PubMed1986

A trans-acting mechanism represses the expression of the major transplantation antigens in mouse hybrid thymoma cell lines.

We have fused an H-2- thymoma (BM5R.9) with an H-2+ thymoma (BW5147) and have found that many of the resulting hybrids exhibit an H-2- phenotype. In several hybrids that were analyzed in detail, this phenotype is related to the absence of steady-state H-2 mRNA and shows some instability, possibly related to the loss of chromosomes in segregants. We conclude from our studies that BM5R.9 cells display a trans-acting mechanism that can repress the expression of H-2 antigens, and that the gene(s) causing the repression are not located on chromosome 17. This mechanism is not sufficient to explain the H-2- phenotype of BM5R.9, for which an additional, cis-acting process, must be postulated. We discuss these results in the context of the regulation of expression of the major class I transplantation antigens.

Animals↗
PubMed1986

Regulation of thymocyte proliferation and survival by deoxynucleosides. Deoxycytidine produced by thymic accessory cells protects thymocytes from deoxyguanosine toxicity and stimulates their spontaneous proliferation.

Deoxyguanosine (dGuo) inhibits thymic blast DNA synthesis and then induces thymocyte cell death. The dGuo inhibitory action, measured with four different assays (spontaneous thymidine incorporation, immunofluorescent detection of 5-bromodeoxyuridine incorporation, dye exclusion, tetrazolium salt cleavage), was suppressed in the presence of supernatants from cultures containing phagocytic cells. In particular, we studied the anti-dGuo activity in supernatants from thymic reticulum cultures (TRS) and in those from phagocytic cells isolated from TR cultures (P-TR). The anti-dGuo substance was identified as deoxycytidine (dCyd) by high performance liquid chromatography and other physicochemical studies. Secretion of dCyd by P-TR is accompanied by thymidine but not by purine nucleoside secretion. A dual mechanism of thymocyte rescue by dCyd was demonstrated by a study of the dose-dependencies of dCyd-mediated prevention and reversal, respectively, of the dGuo inhibition. In addition to this exogenously added anti-dGuo action, dCyd and dCyd-containing TRS induced significant stimulation of spontaneous thymic blast proliferation, and the kinetics of both effects were identical. These findings might suggest that a major role of thymic phagocytic cells is the supply of pyrimidine nucleosides to thymocytes resulting in the maintenance of proliferation and protection of at least some thymic blasts from the toxic effects of dGTP accumulation. The role of this system in the intrathymic selection process is discussed.

Animals↗
PubMed1986

Increased Con-A-induced thymocyte proliferation and de novo Qa-2 antigen expression in Qa-2-depleted thymocyte cultures.

We have recently shown that thymocyte activation is associated with a strong increase of Qa-2 antigen expression. Contrary to what could be predicted from these results, the initial depletion of Qa-2+ cells from PNA- thymocytes increases the Con-A-induced proliferation. Qa-2+ cells not only reappeared after activation, but were enhanced in Qa-2-depleted PNA- cells compared to the control. The newly formed Qa-2+ population contained a higher percentage of Lyt 1+2- cells and thus seems to be different from the Qa-2+ pool initially present.

Animals↗
PubMed1985

Multiple marker analysis of resting and activated murine thymocytes.

The expression of differentiation antigens and terminal deoxynucleotidyl transferase (TdT) were studied with cultured murine thymocytes using the immunofluorescent technique. Four different culture conditions were used: i) medium alone; ii) addition of Con A; iii) addition of Con A stimulated splenocyte supernatant (CSS); iv) addition of both Con A and CSS. The percentages of viable cells and their absolute numbers were evaluated. TL expression was strongly decreased in all four cases, with the almost total disappearance of TL+ cells in Con A + CSS-stimulated cultures. In contrast, TdT+ cells remained well represented. The distribution of cells expressing or not expressing Lyt antigens varied according to the different culture conditions. The only cell type to exceed its initial number was the TdT+ Lyt- one, in cultures performed in the presence of Con A + CSS. The absolute number of Qa-2+ cells was initially reduced by 50% after 2 h in culture, and was then maintained for 3 days. This number was increased only in the presence of Con A + CSS. Therefore, Qa-2+ cells appear much more resistant than the other thymocyte subpopulations in culture, and even proliferate under stimulating conditions. The proliferating Qa-2+ cells also expressed TdT, as detected by the immunofluorescent technique, but enzymatic detection of the enzyme gave unsignificant results. Proliferating Qa-2+ cells presented either Lyt1 or both Lyt1 and Lyt2 antigens. The expression of H-2K antigen was also strongly increased in stimulated cultures, but Qa-4 and Qa-5 antigens could not be detected. These results suggest that Con A and CSS stimulated both mature cells and precursor cells (as shown by TdT expression). The possible relevance of these findings for the theories of thymocyte ontogeny is discussed.

Animals↗
PubMed1985

Relationships between terminal transferase expression, stem cell colonization, and thymic maturation in the avian embryo: studies in thymic chimeras resulting from homospecific and heterospecific grafts.

Terminal deoxynucleotidyl transferase (TdT) can be detected in 11- to 12-day-old embryonic chick thymuses 5 to 6 days after the first influx of lymphoid stem cells into the thymic rudiment. To identify the main factors of TdT induction, grafting experiments were devised in such a way that the age of the grafted thymus and that of the host were different. Uncolonized embryonic chick thymuses were grafted into chick hosts of different ages. Under these conditions, lymphoid differentiation arose from host lymphoid stem cells (LSC) invading the thymic rudiment. TdT immunofluorescent detection in the first wave of thymocytes showed that the percentages of TdT+ cells were related to the total age of the explant and not to the age of the host (11 to 17 days). Similar results were obtained when the chick thymic rudiment was transplanted into quail embryos, showing that quail LSC have TdT inducibility similar to that of chick LSC while developing in a chick thymic environment. Colonized chick thymuses were also grafted into quail embryos to compare the TdT inducibility of the first lymphoid generation (of chick type) and of the second (of quail origin), taking advantage of the different chromatin structure of quail and chick cells. In these experiments, the majority of chick cells remained TdT negative for as long as 10 days, whereas most lymphocytes of the second generation became TdT+ soon after their arrival in the grafted thymus. Therefore, during embryonic life, most TdT+ cells were derived from the second wave of stem cells, but some early stem cells were also able to acquire the enzyme. In a final series of experiments, early thymic rudiments were cultured in vitro with 14- to 16-day-old bone marrow and then grafted into 3-day-old host embryos. Under these conditions, bone marrow LSC contributed to a variable proportion of the first generation of thymocytes. The percentage of TdT+ cells among the progeny of these bone marrow stem cells was found to be two times higher than that of thymocytes derived from host LSC. These results suggest that, in addition to intrathymic environmental factors, the origin of LSC influences the frequency of TdT expression in their progeny.

Animals↗
PubMed1980

Terminal deoxynucleotidyl transferase during the development of chicken thymus.

Antibodies specific for chicken terminal deoxynucleotidyl transferase (TdT) were used to develop immunoperoxidase and immunofluorescence assays. The cellular distribution and localisation of TdT during the development of chicken thymus were studied. TdT began to appear in the embryonic thymus in the cytoplasm of large cells, between 11 and 12 days of incubation. Thereafter, the proportion of TdT-positive cells increased and TdT was detected in both nucleus and cytoplasm. The first appearance of TdT positive cells, their increasing proportion and the intracellular localisation of TdT will be discussed in correlation with the developmental stages of the thymus.

Animals↗
PubMed1979

Acute lymphoblastic leukemia with pre-B-cell characteristics.

Blast cells from 6 of 50 patients with acute lymphoblastic leukemia (ALL) displayed intracytoplasmic mu chains in the absence of detectable light chains and surface immunoglobulins. These cells also expressed lalike and common ALL antigens. Terminal deoxynucleotidyltransferase was detectable in 2 of 5 cases tested. These blast cells are probably related to early B-cell precursors (pre-B cells). In 4 of 6 cases the disease had a tumoral presentation; the prognostic significance of this new subgroup, which accounts for 20% of patients with non-T non-B ALL, remains to be established.

Antigens, Neoplasm↗
PubMed1979

Human T cell differentiation antigens and correlation of their expression with various markers of T cell maturation.

Two sets of differentiation antigens are demonstrated on human T cells by using 11 heterologous anti-human antisera raised against various normal and malignant T cells. The two antigenic determinants from the first set of differentiation antigens are expressed only on thymus cells and on T lymphoblasts, whereas the two antigenic determinants from the second set are expressed on blood T cells, Sezary cells, T.CLL cells, and thymus cells. Four T cell phenotypes are thus defined; two phenotypes are expressed only by T lymphoblasts, whereas the other two phenotypes are expressed both by normal and malignant T cells. Moreover, a clear-cut relationship exists between the four T cell antigenic phenotypes and two other markers of T cell differentiation: terminal deoxynucleotidyl transferase and peanut agglutinin. Two phenotypes are linked with the presence of TdT, one phenotype is linked with the affinity for PNA, and the fourth phenotype is correlated with the absence of both markers.

Acute Disease↗
PubMed1979

Subsets of malignant lymphomas in children related to the cell phenotype.

We studied the lymphomatous cells of 39 children presenting with the classical features of malignant lymphoma. Twenty-two had T lymphoblasts. We could classify these patients into three subsets: The T lymphoblasts from children group 1 displayed antigen(s) shared by a thymocyte subpopulation, had terminal deoxynucleotidyl transferase (TDT), but no affinity for peanut agglutinin (PNA). The T lymphoblasts from children group 2 lacked the thymocyte antigen(s), had no TDT, but showed affinity for PNA. The T lymphoblasts from children group 3 displayed mature T-cell antigens, had no TDT, and no affinity for PNA. Children from the three groups were similar in terms of clinical presentation, age and sex distribution, and cell morphology; however patients from the three groups might have a different prognosis. Fourteen children had B lymphoblasts that, in half of the cases, had affinity for Helix pomatia agglutinin. Three patients had lymphoblasts lacking specific marker. Two of them had cells displaying an antigen found on common acute lymphoblastic leukemia cells and had TDT.

Adolescent↗