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Biomedical subjects

A Coutinho

Publications and source records attributed to A Coutinho.

At least 91 records · Page 5Linked to original sources
PubMed1994

Skewed V beta TCR repertoire of CD8+ T cells in murine Trypanosoma cruzi infection.

We have followed CD4 and CD8 TCR V beta repertoires during the acute phase of Trypanosoma cruzi infection in a resistant mouse strain (C57BL/6). No major changes were found in the V beta TCR distributions analyzed (covering roughly 40% of the TCR repertoire) in peripheral CD4 T lymphocytes, confirming the polyclonal nature of CD4 T cell responses. In contrast, in most animals, an over-representation of V beta 5 and V beta 14 TCR families was disclosed in the CD8 T cell compartment, superimposed on a predominantly polyclonal response. The preferential expansion of V beta 5+CD8+ T cells was also observed after infection of sensitive (C3H/HeJ, BALB/c) mouse strains. These observations suggest the existence of CD8 T cell-directed superantigenic activities associated with parasites.

Animals↗
PubMed1994

Global analysis of antibody repertoires. 1. An immunoblot method for the quantitative screening of a large number of reactivities.

This paper describes a procedure for analysing multiple antibody reactivities that explores a commercially available immunoblot system, and is based on a double staining of nitrocellulose membranes, revealing both antibody reactivities and the migration position of the blotted proteins in the membrane. Quantification of both stainings by densitometry allowed the accurate superposition of the immunoreactivity and total protein profiles of each lane. Moreover, the protein stainings of the different lanes could be adjusted with a simple-scale transformation algorithm, correcting for possible distortions during electrophoretic migration, and allowing for the precise comparison of the immunoreactivity profiles in different lanes. The procedure is discriminatory enough to identify unique reactivity patterns in random pools of 10(4) activated B cells, and to define strain-specific natural antibody repertoires. The utility of this immunoblot method as an assay for simultaneously scoring multiple reactivities to hundreds of antigens in complex mixtures of antibodies, and thus defining antibody repertoires in a global manner, is discussed.

Animals↗
PubMed1994

VH-gene family dominance in ageing mice.

The cellular composition and VH-gene family repertoire were compared in different B-cell compartments from young adult (8-12 weeks) and old (18-24 months) C57BL/6 and BALB/c mice. Ageing mice were found to have a higher frequency of peripheral mature B cells utilizing genes from a single VH-gene family. While in each individual old C57BL/6 mice cells expressing the VH J558 gene family consistently were over-represented, a marked individual variation was observed in old BALB/c mice with increased frequency of either the VH J558, Q52 or J606 families. Aged mice were found also to have a reduced number of bone-marrow pre-B cells and an augmented number of splenic Ig-secreting cells. These results suggest that old mice express less diversified antibody repertoires possibly as a consequence of reduced input from precursors and increased peripheral selection, which may be responsible for the progressive establishment of immunodeficiency.

Aging↗
PubMed1994

Live adult worms detected by ultrasonography in human Bancroftian filariasis.

Ultrasonographic examination of the scrotal area was performed in 14 asymptomatic individuals with bancroftian filariasis and microfilaremia. While in seven subjects (50%) the ultrasonographic findings were normal, lymphatic dilation and tortuosity were observed in the other seven. In these vessels, structures with peculiar aleatory movements (filaria dance sign) were detected. A segment of the lymphatic tract containing these mobile intraluminal structures that was resected surgically from the left spermatic cord of one individual confirmed that these structures were living Wuchereria bancrofti adult worms (two females and one male). Our study demonstrates for the first time the feasibility of using a low-cost, widely available, noninvasive technique (ultrasonography) to detect and monitor living adult worms and lymphatic dilation in patients with bancroftian filariasis.

Adolescent↗
PubMed1994

Signal antonymy: a mechanism for apoptosis induction.

The unfolding of the developmental programme and the organization of multicellular organisms require that cell numbers in differentiating and differentiated tissues are regulated. This is done by two distinct processes : control of cell proliferation and differentiation to a post-mitotic stage; and control of survival in post-mitotic cells. It is argued that elimination of cells by programmed cell death (PCD), which operates in both cases, is regulated by distinct mechanisms: PCD in post-mitotic cells corresponds to 'death-by-default' of (counter apoptotic) survival signals (Raff, 1992), while apoptosis in cycling cells, or in resting cells submitted to proliferative signals, results from antonymy in signalling pathways, i.e. a situation where a cell simultaneously engages into incompatible pathways of proliferation and cell cycle arrest. Antonymy arises in cells irreversibly committed to either proliferation or arrest and responding to a contradictory signal. In turn, the irreversible commitment arises by uncoupling of signal transduction from co-ordinated pathways (as in transformed cells with constitutive expression of growth-associated genes or in terminally differentiated post-mitotic cells).

Journal Article↗
PubMed1993

Xid-associated resistance to experimental Chagas' disease is IFN-gamma dependent.

In contrast to normal Balb/c, Balb.Xid immunodeficient mice are naturally resistant to Trypanosoma cruzi infection. Thus, Balb.Xid mice control parasitemia, do not show the characteristic wasting in the acute infection and develop no tissue pathology in the skeletal or cardiac muscles in the chronic phase of disease. By in situ hybridization and semiquantitative polymerase chain reaction, the expression of IL genes in spleen cells from Balb/c and Balb.Xid mice were compared after T. cruzi infection. The results showed that Balb.Xid mice produce considerably higher levels of IFN-gamma, IL-2, and IL-4, but lower levels of IL-10, from as early as 4 days after parasite injection. By day 12 of the infection, although IFN-gamma, IL-2, and IL-4 expression was now comparable in both groups, IL-10 levels continue to be lower in Balb.Xid than in control Balb/c animals. The central role of IFN-gamma in the resistance to T. cruzi was confirmed by treatment of Balb.Xid mice with anti-IFN-gamma antibodies that reestablished susceptibility and lead to increased parasitemia and mortality.

Animals↗
PubMed1993

Para-aortic splanchnopleura from early mouse embryos contains B1a cell progenitors.

Definitive erythropoiesis in birds originates from stem cells that emerge in the splanchnopleural mesoderm near the embryonic aorta. The yolk sac is still generally held to be the unique provider of haematopoietic stem cells during mammalian ontogeny, although there may be an alternative intraembryonic source of stem cells in the mouse fetus. Here we search for a possible non-yolk-sac source of stem cells by grafting intraembryonic splanchnopleura from 10- to 18-somite mouse embryos into adult immunodeficient SCID mice. We find significant amounts of donor-derived serum IgM, normal numbers of IgM-secreting plasma cells, and the B1a (IgM(a)brightB220dullCD5+) cell subset to be fully reconstituted by donor progenitors 3 to 6 months after engraftment. The haematogenic capacity revealed in our experiments is present in a previously unrecognized site, the earliest described in the embryo, 12 hours before fetal liver colonization.

Animals↗
PubMed1993

Functional double-negative T cells in the periphery express T cell receptor V beta gene products that cause deletion of single-positive T cells.

A proportion of peripheral T cells lack surface expression of the CD4 or CD8 coreceptor molecules and hence are designated as " double negative" (DN). Most DN T lymphocytes express the gamma/delta T cell receptor (TcR), but a minor fraction of them, in both humans and mice, express the alpha/beta TcR. Whereas alpha/beta+ DN T lymphocytes are infrequent (< 1%) in conventional lymphoid organs (spleen, blood, lymph node), they account for two-thirds of the T cells residing in adult bone marrow. Analysis of the TcR V beta repertoire expressed by peripheral DN T cells revealed a high frequency of cells bearing autoreactive TcR that cause deletion of "single-positive" (SP) (CD4+CD8-or CD4-CD8+) T cells. Peripheral DN cells thus represent a cell type that is relatively resistant to clonal deletion. Furthermore, such cells have not been inactivated (anergized) in vivo since they proliferate and secrete interleukins in response to cross-linking by monoclonal antibodies specific for these V beta gene products that are deleted in SPT cells. These results might help to understand the association of peripheral expansion of DN cells and development of autoimmune diseases.

Animals↗
PubMed1993

Suppression of B cell differentiation by ligation of membrane-bound IgM.

Using B cells from the transgenic mouse line B6-Sp6 and control littermates, stimulated by lipopolysaccharide (LPS) under novel culture conditions that provide for the response of all B cells, we show here that specific ligation of the surface IgM molecules always results in inhibition of terminal differentiation and immunoglobulin secretion by activated cells, regardless of the ligand. Thus, monoclonal antibodies to (a) the CH region of Ig (anti-mu and anti-allotype), (b) the C kappa region, (c) the V region (anti-idiotype) of surface IgM, as well as (d) multivalent antigen (2,4,6-trinitrophenyl-bovine serum albumin), all show similar effects and dose-response curves. IgD-negative transgenic B cells are equally sensitive to IgM ligation-dependent inhibition, as control (IgD-positive) B cells. The allotype specificity of this inhibition, assessed by using anti-mu allotype reagents to inhibit and assay the responses, suggests that B cells expressing transgenic or endogenous IgM in transgenic B6-Sp6 mice are largely independent populations. These observations establish that anti-IgM antibodies in conjunction with appropriate LPS stimulation, provide a universal model system for functional characterization of B cell responses.

Animals↗
PubMed1993

Evidence for selective pressure in the appearance of monoclonal immunoglobulins during aging: studies in M54 mu-transgenic mice.

Serum monoclonal immunoglobulins (M-Ig) appear during aging but little is known about the immunological factors which lead to their development. We have investigated whether such M-Ig occur as a clonally random process or result from V-region-directed selective pressures. We have analyzed a mu-transgenic mouse strain in which over 95% of all splenic B cells express the transgenic mu chain. All endogenous repertoire and mu-chain diversity are generated from the 5% of the B cells which express endogenous mu chains. Not one of the M-Ig detected in these mice were of transgene origin alone; 11 of the 14 M-Ig did not express a mu chain and none of the mu chain containing M-Ig expressed the transgene allotype alone. This observation suggests that the B cells giving rise to M-Ig are heavily selected from among the small number of B cells which express endogenous Ig. The selective factors that might act on the endogenous B cell pools are discussed.

Aging↗
PubMed1993

Global analysis of antibody repertoires. II. Evidence for specificity, self-selection and the immunological "homunculus" of antibodies in normal serum.

The serum IgM repertoires of C57BL/6, DBA/2 and BALB/c mouse strains were analyzed using a recently developed global and quantitative assay that measures antibody reactivities to a very large number of antigens. A characteristic repertoire could be assigned to each strain. The different repertoires could be successfully classified with multivariate statistics. Many common reactivities were also observed among the different strains, which allows the definition of a mouse-specific repertoire. Analysis of human sera support this notion. To investigate the impact of minor genetic differences on the serum IgM repertoire, the congenic strains B10.D2/oSn and B10.D2/nSn, which differ in the expression of the C5 component of complement, were analyzed. The two strains could be separated based on the reactivity profiles obtained. The analysis of the results reveals that many antigenic proteins are not recognized at all by natural antibodies, while others are disproportionately reactive, the resulting patterns giving rise to what could be the definition of an "immunological homunculus". The relevance of this type of analysis for clinical applications is discussed.

Adult↗
PubMed1993

Are lymphocytes concerned with our definition of idiotypes?

For some, idiotypes are interesting as markers of individual molecules, providing the basis for a taxonomy of B- and T-cell clones. For us, idiotypes are components of a larger network structure of variable regions, and their shapes are of significance because they establish connectivity. Each unique specificity per se is less interesting, for it is interchangeable without altering network organization. These issues are critical for delineating concepts of autoimmunity and for choosing between 'nonspecific' and 'targeted' approaches of immunoglobulin therapy in autoimmune diseases.

Animals↗
PubMed1993

V region dependent selection of persistent resting peripheral B cells in normal mice.

In this study, we compare the VH gene family repertoire of persistent long-lived splenic B cells with that of the whole splenic B cell compartment. Persistent long-lived B cells were obtained by two independent strategies. Firstly, we studied cells that persist in the peripheral pools with or without cell division. We have transferred mature lipopolysaccharide (LPS)-reactive splenic B cells into LPS non-responder recipients and studied the donor population that could be recovered in host mice at differing time intervals after cell transfer. Secondly, we studied non-cycling resting long-lived B cells. These cells were obtained in normal mice after cytostatic treatment with hydroxyurea and in mice transgenic for the HSV-1 thymidine kinase gene after treatment with the anti-herpetic ganciclovir. Studying the VH gene family usage at the single level by in situ hybridization, we found that persistent B cells show an increased expression of the VHJ558 family and a diminished representation of the VH7183 family. These results demonstrate that in a normal non-immunized mouse, B cell survival and persistence in the resting state results from V region dependent selection.

Animals↗
PubMed1993

Development of B cells secreting endogenous or transgene-encoded immunoglobulins in H-chain transgenic mice.

The development of splenic B cells secreting transgene-encoded or endogenous immunoglobulin (Ig) was analysed in the mu heavy (H-)chain transgenic mouse line M54. The results show that cells secreting endogenous Ig are not detectable during the perinatal period, even after lipopolysaccharide stimulation in vitro. At this time, transgene-secreting cells are readily detectable and keep increasing with age of the animals. After a few weeks of age cells secreting endogenous Ig appear in the spleen and keep increasing with age, reaching numbers comparable to non-transgenic littermates by 5 weeks of age. Thereafter, the proportion of transgene-secreting B cells decreases. We conclude that the preferential expression of endogenous Igs by secreting B cells in the adult does not result from peculiar genetic features of those cells, but from age-dependent cellular selection operating on all B cells.

Age Factors↗
PubMed1993

The role of thymic epithelium in the establishment of transplantation tolerance.

From experimental observations on induction of transplantation tolerance, we discuss a model that accounts for tissue-specific tolerance to antigens not expressed inside the thymus. It is postulated that antigens presented to differentiating T cells by thymic epithelium (or at large within the thymic environment) positively select and activate self-reactive T cells. A developmental program and/or prevalent conditions in the thymic environment restrict the proliferative potential and the class of effector functions that can be exerted by differentiating T cells activated in the thymus. These do not mediate inflammatory or cytolytic activities, but instead will produce the appropriate mediators to inhibit aggressive effector activities by other T cells activated in their proximity. Such "regulatory" functions will be locally expressed at the periphery upon recognition of tissue antigens shared with the thymus, towards newly formed thymic emigrants directed at tissue-specific antigens expressed by the same "target" cells. This mechanism imposes "dominant tolerance", based on specific self-recognition and predominantly established in the embryonic and neonatal period. Throughout life, the process of thymic positive selection results in all newly-formed T cells being susceptible to such suppressive mechanisms, but becoming increasingly refractory with time in the resting, post-differentiative stage. Absence of antigen (nonself) in the embryonic and neonatal life therefore allows for the accumulation of such "suppression-resistant" antigen-reactive T cells that will mount aggressive responses upon antigenic exposure. Tolerance or immunity thus represent two classes of specific immune responses, the relative predominance of which is determined by the frequency of each type of effector T cell, representing the antigenic overlap between thymic and peripheral tissues, as well as the frequency of tissue-specific T-cell generation, and the kinetics of peripheral antigenic exposure. Tolerance induced by hemopoietic cells to all other tissues is also "dominant" and based on thymic colonization and persistence of antigenic cells, with the consequent positive selection of regulatory T cells and peripheral conditions for the establishment of suppression. Upon this simple model, that ensures "interclonal class regulation" by "bridging" regulatory and effector T cells through the recognition of different antigens on the same target cell, other mechanisms which are based on V-region interactions among T cells (Ben-Nun et al. 1981, Pereira et al. 1989, Webb & Sprent 1990, Gaur et al. 1993) might well operate to ensure "dominant tolerance" by self-reactivity and class regulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗