Search PubMed⌕ Search

Biomedical subjects

B Rocha

Publications and source records attributed to B Rocha.

At least 19 recordsLinked to original sources
PubMed1992

Selection of intraepithelial lymphocytes with CD8 alpha/alpha co-receptors by self-antigen in the murine gut.

We have studied T-cell receptor (TCR) and alpha/alpha CD8 expression in thymus-independent intraepithelial lymphocytes (TI IELs) from the gut of mice bearing transgenic (TG) TCR alpha beta specific for the male antigen, presented by H-2Db class I major histocompatibility complex (MHC) molecules. In contrast to TCR+ alpha beta cells differentiating in the thymus (from CD4+CD8+ precursors to CD4+CD8- or CD4-CD8+ progeny), TI IELs are not deleted by self-antigens, nor are they positively selected in the absence of the specific peptide. On the contrary, recognition of the antigen in the context of self-MHC is required for selection and granular differentiation of CD8+ TI IELs. Our results also show that, in contrast to the thymus, expression of the beta TG does not block expression of endogenous TCR gamma delta genes in TI IELs. The size of this gut IEL subpopulation and its difference in mechanisms of repertoire selection demonstrate the existence of a major extrathymic pathway of T-cell differentiation, the role of which remains to be elucidated.

Animals↗
PubMed1992

C-fos immunoreactivity in the brain following unilateral electrical stimulation of the dorsal periaqueductal gray in freely moving rats.

C-fos immunoreactivity was used to reveal brain areas in which neurons were influenced by electrical stimulations applied to the dorsal periaqueductal gray. These stimulations were applied in freely moving rats so that the resulting behaviors could be observed. Shortly afterwards, the brains of the rats were processed for C-fos immunoreactivity. In order to determine the specificity of the brain areas thus labeled, control stimulations were applied to the ventral tegmental area of other rats. Immunoreactive cells were found surrounding the tip of the stimulation electrode within a radius of 0.5 mm. This labeled area extended further along the rostro-caudal axis than along the medio-lateral or dorso-ventral axis in the periaqueductal gray. Distally, clusters of labeled cells were found ipsilaterally in the caudal periaqueductal gray extending to the nucleus cuneiformis, and bilaterally in the locus coeruleus and supramamillary decussation. More widespread labeling was found in most hypothalamic subareas and in the lateral habenula. The labeled brain areas following ventral tegmental area stimulations were totally distinct, and comprised the medial forebrain bundle, the nucleus accumbens, the vertical limb of the diagonal band and the medial septum. The pattern of labeling produced by periaqueductal gray stimulations was therefore specific, and provided information about brain structures involved in the motivational and behavioral effects of such stimulations.

Animals↗
PubMed1992

Conditioned place preference induced by Ro 16-6028, a benzodiazepine receptor partial agonist.

A place conditioning situation was used to assess the putative affective properties of benzodiazepine receptor ligands in the rat. The benzodiazepine receptor partial agonist Ro 16-6028 induced a conditioned place preference, suggesting that this compound has rewarding properties. The benzodiazepine receptor antagonist Ro 15-1788 induced neither place preference nor aversion, but prevented the place preference induced by Ro 16-6028, suggesting that the rewarding effects of Ro 16-6028 are due to its action on the benzodiazepine receptor. The benzodiazepine receptor full agonist diazepam did not induce a conditioned place preference in our hands, in contrast with previous studies. The sensitivity of place conditioning with benzodiazepine ligands to situational factors, such as the existence of a preconditioning preference, is discussed.

Animals↗
PubMed1992

The extrathymic T-cell development pathway.

In normal mice, not all T-lineage cells are generated and selected in the thymus; an alternative, extrathymic, development pathway exists. Extrathymic T cells are rare in the spleen and lymph nodes, but are abundant in some tissues, such as the gut. Here, Benedita Rocha, Pierre Vassalli and Delphine Guy-Grand discuss the rules of selection of extrathymic T cells, assess the possible role of these cells in the defence of epithelial integrity and their potential role in autoimmune disease.

Animals↗
PubMed1991

An unusual lineage of alpha/beta T cells that contains autoreactive cells.

In male mice that express a transgenic alpha/beta T cell receptor (TCR) specific for a male-specific peptide presented by class I Db major histocompatibility complex (MHC) molecules, we describe an unusual lineage of alpha/beta T cells that are thymus dependent but do not require selection by Db MHC molecules on thymic epithelium in the absence of the specific peptide (positive selection). These cells express the transgenic alpha/beta TCR and have the CD4-8- or CD4-8low phenotype. Cells with the latter phenotype are only detected when hemopoietic cells express both the male-specific peptide as well as Db MHC molecules. In fact, these cells are autoreactive, as they expand relatively slowly after transfer into male nude mice. Also in male but not female alpha/beta TCR transgenic mice, the CD8+ cells with the transgenic TCR bear the Pgp1 marker characteristic of mature T cells activated by antigen. CD4-8- as well as CD4-8low cells do not respond significantly when cultured with male stimulator cells but proliferate vigorously when stimulated by TCR antibodies. By this latter criterion, cells in the periphery of male alpha/beta TCR transgenic mice differ from mature male-specific T cells from female alpha/beta TCR transgenic, which become intrinsically anergic when transferred into male nude mice and cannot be stimulated significantly by TCR antibodies. Thus, intrathymic deletion does not eliminate all autoreactive T cells and it is possible that cells with an apparently "benign" autoreactivity may be involved in certain forms of autoimmunity.

Animals↗
PubMed1991

Peripheral selection of the T cell repertoire.

T lymphocytes undergo selection events not only in the thymus, but also after they leave the thymus and reside in the periphery. Peripheral selection was found to be dependent on T cell receptor (TCR)-ligand interactions but to differ from thymic selection with regard to specificity and mechanism. Unlike thymic selection, peripheral selection required binding of antigen to the TCR, and it induced expansion of T cell clones. Tolerance to self antigens that are restricted to the periphery occurred through the elimination of self-reactive T cells and by the clonal anergy, which was associated with down-regulation of the alpha beta TCR and CD8.

Animals↗
PubMed1991

The V beta repertoire of mouse gut homodimeric alpha CD8+ intraepithelial T cell receptor alpha/beta + lymphocytes reveals a major extrathymic pathway of T cell differentiation.

Gut intraepithelial lymphocytes (IEL) contain two independent T cell receptor alpha/beta + T cell populations, with different V beta repertoires. In DBA/2 mice (Mlsa, IE+), the CD4+ and heterodimeric alpha/beta CD8+ thymodependent T cell pool shows the same deletion of V beta 6, 8.1, and 11+ cells as found in peripheral lymphoid organs. In contrast, such deletions are not observed in the pool of IEL bearing homodimeric alpha CD8+ chains, in which these V beta families are frequently observed in high amounts. The size of this gut homodimeric alpha CD8+ IEL pool and its different V beta repertoire selection demonstrate the existence of a major extrathymic pathway of T cell differentiation with a gut-restricted localization. The large amount of the thymo-independent, homodimeric alpha CD8+ IEL found in the small bowel may contribute to a first line of defense against exogenous superantigens.

Animals↗
PubMed1991

Post- thymic in vivo expansion of mature alpha beta T cells.

To discriminate whether peripheral T cell expansion is a property of pluripotent T cell precursors or of T lymphocytes precommitted to the expression of a single T cell receptor, we have evaluated the repopulation capacity of T lymphocytes expressing defined V beta gene products after transfer into syngeneic nude mice. The results showed no difference in the expansion potential of cells expressing different V beta s. The frequency of cells bearing different V beta gene products in the donor and the expanded cell populations are very similar, even when sorted populations enriched or deleted in T cells expressing a defined V beta gene product were used as a source of donor cells. These results demonstrate that peripheral T cells expressing alpha beta TCR are fully competent of extensive division in the peripheral pools.

Animals↗
PubMed1990

Characterization of V beta-bearing cells in athymic (nu/nu) mice suggests an extrathymic pathway for T cell differentiation.

In the present article, the expression of the T cell receptor (TcR) beta chain and other T cell molecules was evaluated in surface immunoglobulin-negative spleen cell populations of young and old BALB/c and C57BL/6 nude mice, using a panel of monoclonal antibodies. The results obtained show that in young nude mice, most Thy-1high cells do not express other T cell markers. These mice have, however, a sizable population of Thy-1low cells with the same phenotype of alpha/beta+, CD4-CD8- thymocytes or MRL/lpr peripheral T cells, expressing predominantly genes of the V beta 8 family. The evolution of alpha/beta+ cells in aging nudes is strongly suggestive of an extrathymic pathway of differentiation of these cells since (a) the acquisition of high density TcR and CD3, as well as Thy-1 or CD4CD8 antigens at the cell surface of nude V beta+ T cells is not simultaneous; (b) alpha/beta+ cells in nude mice co-express other T cell markers at random and, even in old mice, they never completely resemble to the predominant high Thy-1+ CD3+ TcR alpha/beta+, CD4+CD8+ cells of euthymic controls; and (c) BALB/c nude T cells express V beta 11 genes, that are deleted in euthymic BALB/c mice. This latter finding may also indicate differences in the mechanisms of selection of T cells specificities in the thymus vs. the peripheral pools.

Age Factors↗
PubMed1990

Accumulation of bromodeoxyuridine-labeled cells in central and peripheral lymphoid organs: minimal estimates of production and turnover rates of mature lymphocytes.

Daily lymphocyte production in both central and peripheral lymphoid organs was evaluated by associating in vivo incorporation of bromodeoxyuridine (BrdUrd) with cell surface labeling and multi-parameter flow analysis. At least 10% of mature T and B lymphocytes are generated every 24 h. The kinetic behavior of these cell populations differs, however, in that mature B cells are generated predominantly in the precursor compartments of the bone marrow, while most mature T cell generation occurs at the periphery. Therefore, peripheral expansion is the major mechanism of mature T cell production in the adult mouse. By following the accumulation of BrdUrd-labeled cells in peripheral lymphoid organs we found that the progeny of the daily lymphocyte production was sufficient to renew 30%-40% of all peripheral T and B cells every 48 h, demonstrating a high turnover rate of mature lymphocytes. We also examined the conditions of BrdUrd labeling of cycling cells in vivo. We found that while greater than 90% of bone marrow and thymus cells in S phase were labeled with a single injection of BrdUrd, in peripheral lymphoid compartments 70% of T and B cells in S failed to incorporate BrdUrd. Particular schedules of BrdUrd administration were required to overcome the low labeling efficiency of mature cells in vivo. Prolonged BrdUrd administration, however, had toxic effects on resident cells. The low labeling efficiency of BrdUrd incorporation by mature cells, as well as its potential toxicity during prolonged administration, may explain controversial results obtained by the different strategies used to study lymphocyte population dynamics.

Animals↗
PubMed1989

Peripheral T lymphocytes: expansion potential and homeostatic regulation of pool sizes and CD4/CD8 ratios in vivo.

Peripheral T lymphocytes are self-renewable cell populations since, when transferred into syngeneic T cell-deficient athymic mice, they expand in the absence of exogenous antigen stimulation. Quantification of the expansion potential of CD4+ cells by transfer of the same population into successive host mice shows that these cells are able to divide up to 56 times in vivo. Therefore, as a population, CD4+ cells can increase in size 8 x 10(5)-fold, an expansion potential of similar magnitude to that previously reported for colony-forming units. Injection of different numbers of T cells at different CD4/CD8 ratios is followed by T cell accumulation to a similar plateau in recipient nude mice. This indicates that peripheral T lymphocytes are tightly regulated by homeostatic mechanisms that control pool sizes and CD4/CD8 ratios, in a manner independent of the cell input into the peripheral compartment. This kinetic behavior of mature T cells permits the maintenance at the periphery of any T cell specificity previously selected in the thymus. The expansion capacity of peripheral T cells may also allow extensive modulation of peripheral T cell specificities, which would confer a major role to post-thymic selection of mature peripheral T cell repertoires.

Animals↗
PubMed1989

Interleukin 2 receptor expression and interleukin 2 production in exponentially growing T cells: major differences between in vivo and in vitro proliferating T lymphocytes.

In the present study we have assessed the growth requirements for in vivo proliferating mature T cells. For that purpose we have selected experimental approaches which allow the study of exponential growth in vivo of a major fraction of T cells, and make it possible to obtain large numbers of T cells in cycle. Two types of growing T cell populations were used: peripheral T lymphocytes, proliferating exponentially after transfer into syngeneic athymic nude mice, and activated T cells in lymph nodes of normal mice draining the site of oxazolone administration. The results obtained show that mature T cell growth in vivo is not accompanied by expression of high-affinity interleukin 2 (IL2) receptor in the majority of activated cells, is not abrogated by in vivo administration of anti-IL2 receptor antibodies or enhanced by the in vivo injection of recombinant IL2, and that in vivo growing T cells do not produce detectable amounts of IL2, as evaluated functionally by limiting dilution assays or the presence of IL2 mRNA, detected by Northern blots or in situ hybridization. The presented data thus indicate that the rules known to apply to T cell activation and proliferation in vitro differ from those used by in vivo growing T lymphocytes, at least in the two systems studied.

Animals↗
PubMed1989

Selection of antibody repertories: transfer of mature T lymphocytes modifies VH gene family usage in the actual and available B cell repertories of athymic mice.

The possible role of T lymphocytes in the selection of antibody repertories was investigated by comparing VH family usage in different B cell compartments of euthymic and athymic B6 mice. Analysis of VH gene family representation at the single cell level by in situ hybridization shows a diminished utilization of the VH J558 family in the effector compartment of the spleen and in small B cells of the lymph nodes of nude mice when compared to euthymic age-matched controls. Transfer of mature T cells from syngeneic donors increases expression of the VH J558 family in these two B cell compartments, not only abrogating the decreased utilization of the VH J558 family found in nude mice but further reinforcing the dominance of this family to levels of expression above those observed in euthymic controls. These changes are already evident by 5 days after T cell transfer and represent a permanent alteration of B cell repertoires as they persist for up to 1 year after T cell injection. Reconstitution of athymic mice with isolated T cell subsets induces different patterns of VH gene repertoires. Thus, while CD4+ cells enhance the expression of the VH J558 family, in CD8+ repopulated mice the utilization of the VH X-24 family increases in the splenic Ig-secreting cell pool. The present findings demonstrate that T lymphocytes modulate the selection of antibody repertoires in normal, non-immunized mice.

Animals↗
PubMed1988

Immature, double negative (CD4-,CD8-) rat thymocytes do not express IL-2 receptors.

IL-2R alpha-chain is expressed on a subset of mouse CD4- and CD8-, double negative (DN) thymocytes. This expression of IL-2R alpha-chain on some DN thymocytes in the mouse has led to the proposal that IL-2 might serve as a principal growth and/or differentiation factor for immature thymocytes. However, previous histologic observations have indicated that IL-2R alpha-chain is not expressed on the subcapsular thymic blasts (an area rich in DN cells) in either huma or rat thymus, whereas all three species display IL-2R expression on a few cells in the thymic medulla. Therefore, we characterized rat DN thymocytes to determine whether they contained an IL-2R+ population. The results show that rat thymic DN cells share several characteristics with mouse DN cells. However, most of the rat strains do not express the IL-2R on DN cells as shown either by immunofluorescence or by IL-2 binding and receptor cross-linking. Thus, the rare medullary IL-2R+ cells were not found in the DN cells. Only in the exceptional F344 rat strain is the IL-2R alpha-chain expressed on a major proportion of thymocytes, including both DN cells and small cortical-type thymocytes. Furthermore, rat DN cells do not contain detectable IL-2 mRNA or cytoplasmic IL-2 activity, thus supporting the conclusion that it is unlikely that IL-2 and IL-2R serve to maintain the proliferation of rat DN thymocytes in vivo. The possible significance of in vivo expression of IL-2R alpha-chain on immature thymocytes in the mouse and in a single rat strain is discussed.

Aging↗
PubMed1988

IL-2-dependent proliferation of thymic accessory cells.

Phagocytic cells of the thymic reticulum are Ia-positive accessory cells continuously produced in long term thymic stroma cultures. We show in the present paper that phagocytic cells of the thymic reticulum have R for IL-2. They share this property with splenic accessory cells produced in vitro by the same technique but have the unique property of proliferating in the presence of rIL-2. This proliferation is not enhanced by Con-A, is not linked to a lymphoid contaminant, and is specifically inhibited by an anti-IL-2R mAb.

Animals↗
PubMed1988

Limiting dilution analysis of interleukin-2-producing mature T cells. Interleukin 2 secretion is an exclusive property of L3T4+ lymphocytes.

Evaluation of lymphokine production by individual activated T cells is necessary to characterize their growth requirements. We have studied interleukin 2 (IL-2) secretion by mature T lymphocytes using a high resolution assay system with the following characteristics: (a) a threshold of IL-2 detection 25 times lower than classic IL-2 titration; (b) the ability to discriminate between IL-2 and IL-4 activities; (c) absence of 'in situ' IL-2 absorption; (d) IL-2 production revealed at the single cell level. By this method an average of 10% of spleen cells, and 75% of L3T4+ cells were detected as producers in a concanavalin A (Con A)-dependent T cell activation system. Our results also suggest the complete restriction of IL-2 secretion to cells with this phenotype. Therefore, factors other than IL-2 must play a major role in Lyt 2+ mitogen-driven, helper-independent T cell proliferation.

Animals↗
PubMed1986

Lymphocyte population kinetics in the mouse.

In a normal dynamic equilibrium, at least half of the peripheral T-cell pool is constituted by lymphocytes which have divided 24-48 h previously, and are therefore rapidly renewed. The renewal of peripheral T cells occurs partly by influx of cells from the thymus and, more importantly, by cell division at the periphery. The cyclic pattern of decay observed for T cells after HU treatment suggests the presence of progenitor-descendent relationships within the peripheral T-cell pool. Peripheral progenitors must contain both cycling and non-cycling cells to account for cell recovery after HU administration in ATx mice. T-cell production at the periphery involves both organized (spleen or lymph nodes) as well as non-organized lymphoid tissue (GALT). The latter may in fact provide the major contribution. Expansion of mature T lymphocytes contributes to clonal persistence at the periphery and to the choice of T-cell repertoires. The importance of post-thymic selection of T-cell repertoires is suggested by the considerable expansion potential revealed by peripheral T cells.

Animals↗