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Biomedical subjects

A Coutinho

Publications and source records attributed to A Coutinho.

At least 253 records · Page 14Linked to original sources
PubMed1983

Differential requirements for activation and growth of unprimed cytotoxic and helper T lymphocytes.

The requirements for activation and growth of T lymphocytes capable of mediating either cytolytic activity or help to B lymphocytes were studied in unprimed splenic T cell populations. The selectivity of expression of Lyt-2 antigens, the reactivity to soluble concanavalin A (Con A), to partially purified interleukin 2 (IL 2, T cell growth factor[s]) and to lectin-pulsed macrophages (M phi) were used in this analysis. Lectin-dependent cytotoxicity assays and a novel method that allows for the detection of all effector helper cells, regardless of their clonal specificities, were used for the functional identification of the responding T cells. The results show a marked contrast between cytolytic and helper T cells in their growth and activation requirements. Thus, while Lyt-2+ cytotoxic T lymphocyte precursors grow exponentially in IL 2 after a short pulse with soluble Con A in the absence of accessory cells, Lyt-2- helper cell precursors completely fail to proliferate under the same conditions and require the continuous presence of lectin-pulsed M phi for significant growth. Furthermore, addition of IL 2 to M phi-stimulated cultures of Lyt-2- cells has no effect. T cells which produce IL 2 have the same growth characteristics as helper cells. In both cases, effector helper functions could be expanded more than 10-fold on a per cell basis by a 5-day-culture period under those growth supporting conditions. The development of effector helper functions, however, was strongly inhibited by the presence of Lyt-2+ T cells.

Animals↗
PubMed1983

The immune response to bacterial dextrans. I. Genetic control of responsiveness.

The in vivo antibody response to the thymus-independent (TI) antigen dextran B512 (Dex) was studied in various mouse strains. We found no non-responder strains but rather that the magnitude of Dex-specific plaque-forming cell and serum antibody responses varied markedly among individual mice, even if these were of the same age and litter and kept in the same environment. This was the case both for mouse strains previously described genetically as high (IgCHb,j) and for those described as low (IgCHa) responders to Dex [14]. In 'low'-responder BALB/c mice, the responsiveness to Dex increased with age, such that a large fraction of these mice responded as well as 'high'-responder C57BL/6 mice. Analysis of aged back-cross populations derived from IgCHb and IgCHa parental strains further substantiated these findings. Thus, all backcross mice, irrespective of IgCH haplotype, responded on the average equally well to Dex. According to our studies, therefore, the assignation of high or low responsiveness to IgCH locus-linked genes cannot be done unequivocally.

Aging↗
PubMed1983

Activation of helper T cells for B lymphocytes in primary mixed lymphocyte cultures.

Normal B10.BR (H-2k, C57B1/6 background) spleen cells, enriched in primary mixed lymphocyte culture (MLC) for antigens of C3H/Tif mice (H-2k, C3H background), induced normal C3H/Tif but not B10.BR B lymphocytes to proliferate and produce Ig. In contrast, normal B10.BR spleen cells enriched in parallel B10.BR anti-C57B1/6 (H-2b) MLC were not able to activate either B10.BR or C57B1/6 B lymphocytes. However, normal B10.BR spleen cells depleted of Lyt2+ cells before initiation of the MLC, and subsequently enriched either for C3H/Tif or C57B1/6 antigens, activated B lymphocytes of the respective mouse strains specifically and equally well. These experiments show that primary MLC gives rise to effector T helper cells that, on recognition of specific alloantigens, activate normal B lymphocytes of the 'stimulator' strain. In response to major histocompatibility complex (MHC) alloantigens, this help is not revealed because of interference by Lyt 2+ lymphocytes. MHC-reactive T helper cells for B lymphocytes, however, participate in these reactions and constitute the predominant population in long-term cultures that are maintained by consecutive in vitro restimulations.

Animals↗
PubMed1982

The production of membrane or secretory forms immunoglobulins is regulated by C-gene-specific signals.

Selective patterns of antibody isotypes are produced in response to thymus-dependent and thymus-independent antigens and mitogens. Together with information on the organization of immunoglobulin CH genes in myelomas, various models on the control of C-gene expression and switch in normal B cells have been proposed but only secreted products or secretory cells have been considered. We report here a dissociation between expression of membrane-bound immunoglobulins and secretion of the same isotype, and in this case describe C-gene specific signals which regulate the production of membrane versus secretory forms of immunoglobulin. These results indicate that regulation of isotypic patterns operate at levels other than immunoglobulin gene structure, and suggest that the secretory phenotype alone is inadequate as the measure of C-gene expression.

Animals↗
PubMed1982

Isotype commitment in the in vivo immune responses. I. Antigen-dependent specific and polyclonal plaque-forming cell responses by B lymphocytes induced to extensive proliferation.

The random recombination and deletion hypothesis for the control of isotype commitment in antibody responses was directly tested in a serial transfer system in vivo. Normal or hyperimmune spleen cells were used in weekly serial transfers with antigen into irradiated recipients until clonal senescence was observed. Antigen-specific and -nonspecific plaque-forming cells of all isotypes were determined at each transfer time. No major changes in the isotypes of specific antibodies were observed for the whole life-span of the transferred cells (9-10 wk), and no indication was obtained for the accumulation of cells transcribing the most 3' members of the C-gene cluster with sustained proliferation. Rather, the dominant isotypes were found throughout the response to be IgG1, IgG2b, and IgG2a. The results imply isotype-specific regulatory mechanisms in the control of Ig class production. These appear to operate as well in the antigen-nonspecific component of the immune response.

Animals↗
PubMed1982

Antigen-independent, IgM-induced antibody responses: requirement for "recurrent" idiotypes.

Anti-idiotypic antibodies (a-Id) were produced in syngeneic mice against two monoclonal IgM antibodies of BALB/c origin, TNP. 11 and SP/603. In plaque inhibition tests, using IgM-secreting hybridoma cells and anti-idiotypic antibodies, these two IgM proteins, as well as the anti-TNP myeloma protein MOPC 460 (IgA) were found to carry non-cross-reactive idiotypes. Analysis of the anti-trinitrophenyl (TNP) plaque-forming cells (PFC) in BALB/c mice, either normal or immunized with TNP-horse red blood cells, revealed that in addition to the MOPC 460 Id, also the SP/603 Id is recurrent and expressed by a fraction of the anti-TNP antibody-secreting cells in all individuals tested. In contrast, the TNP. 11 Id could not be detected in any BALB/c mouse studied. TNP. 11 and SP/603 antibodies were then characterized by their ability to induce an antigen-independent anti-TNP response in normal BALB/c mice. While TNP. 11 was found to be inactive, the same titers of SP/603 IgM induced antigen-specific PFC all of which expressed the SP/603 Id, and increased titers of circulating IgM molecules carrying the same Id, suggesting that "recurrent" but not "nonrecurrent" Id are competent in this respect. A fraction of these SP/603-induced, SP/603-positive anti-TNP antibodies also carried MOPC 460 Id, suggesting expression on the same molecule of idiotypic determinants found on independent non-cross-reactive "recurrent" idiotypes.

Animals↗
PubMed1982

Immunoglobulin C-gene expression. III. Possible induction of specific genetic events in activated B lymphocytes by the polyclonal stimuli driving clonal expansion.

Polyclonal activation of resting B lymphocytes by either lipopolysaccharide or specific helper cells recognizing antigens on B cell membranes results in selective patterns of IgG subclass expression among plaque-forming cells. We have studied the IgG subclasses of plaque-forming cells generated in cultures of purified B cell blasts selected for reactivity to either LPS or helper cells, and restimulated by either lipopolysaccharide, specific helper cells, or as "bystanders", by nonspecific B cell growth factors. Development of IgG1 plaque-forming cells is observed only when clonal expansion is maintained by specific helper cells, whereas IgG3 secretion specifically requires stimulation by lipopolysaccharide and the absence of helper cell activity. Furthermore, exposure of resting B lymphocytes to specific helper cell induces, in 48 h, an irreversible loss of the potential to produce IgG3. Other than showing that helper cell-dependent B cell growth and maturation is more complex than previously suspected, these results suggest that differentiation signals or factors induce specific DNA recombination and deletion events.

Animals↗
PubMed1982

Ontogenic development of B cell reactivities to cooperative cell signals: dissociation between proliferation and antibody secretion.

Cloned helper T cell lines, with specificity for "minor" antigens expressed on all B lymphocyte (and macrophage) surfaces were used to study the postnatal development of B cell reactivity to helper T cell cooperative signals. Such helper T cell populations, upon physiologic interactions with "target" B lymphocytes, activate them polyclonally, allowing for the analysis of functional ontogeny independent of V gene repertoires. Due to the high frequency of responding cells, these methods also offer a high level of sensitivity and permit measurement of B cell proliferation in the absence of antibody production. The results demonstrate that neonatal spleen cells are fully competent to stimulate adult helper T cell responses and that neonatal and adult B cells are comparable in their proliferative responses to cooperative cell interactions. In contrast, a marked deficiency in the ability of neonatal cells to mature to immunoglobulin secretion was observed in the same responses. Since the presence of suppressive activities in neonatal spleen cells could not be demonstrated, it was concluded that "early" B lymphocytes are intrinsically defective in their ability to secrete immunoglobulin upon cooperative induction, whereas they show full competence to expand clonally.

Aging↗
PubMed1982

Intraclonal diversification in immunoglobulin isotype secretion: an analysis of switch probabilities.

The production of all immunoglobulin isotypes except IgD was studied in a large number of single lipopolysaccharide (LPS)-reactive B cell clones. The majority, but not all, of the IgM-producing clones were found to secrete one or more other isotypes. IgG3 and IgG2b were most frequently found while IgA secretion was extremely rare. Many clones produced all four IgG subclasses and the statistical analysis of the data indicates, with a high degree of significance, that single clonal precursors give rise to progenies producing multiple isotypes. By assuming that intraclonal diversification follows the C-gene order in chromosome 12, the absolute switch probabilities of normal, unprimed LPS-reactive B cells can be calculated. The multi-potentiality of C-gene expression was further analyzed at the single cell level: a sizeable fraction of all activated B cells express two different IgG isotypes in the membrane-bound form, indicating consecutive switch events. In contrast, the majority of IgE and IgA secreting cells appear to switch directly from IgM. These results might reflect the functional relevance of S-region homologies in the control of C-gene expression.

Animals↗
PubMed1982

Quantitative aspects of the nonspecific humoral immune response to sheep erythrocytes.

The kinetics and magnitude of the nonspecific humoral immune response was studied at the cellular level in mice immunized with sheep erythrocytes (SRBC). Intravenous injection of the antigen evoked, in addition to a specific anti-SRBC response, a nonspecific response of all immunoglobulin (Ig) classes and subclasses. This nonspecific response peaked on day 4 or 5 after immunization, irrespective of the Ig class. The absolute number of nonspecific Ig-secreting cells induced by immunization varied with the different Ig-classes, and it was not proportional to the background level of Ig-secreting cells of the various classes. The nonspecific IgM-IgG1- and IgG2-response was 3 to 4 times as large as the antigen-specific responses of these classes. The nonspecific IgA-response, however, was many times greater.

Animals↗
PubMed1982

Clonal analysis of the specificity of alloreactive cells: "dominance" of E beta reactive clones.

The present experiments analyze the specificity of cells proliferating in murine mixed lymphocyte cultures (MLC). Lymphocytes from the B10.A(5R) strain, enriched by repeated restimulations with B10.A cells, proliferate specifically in response to B10.BR, B10.A and [B10.A(4R) X B10.A(5R)]F1 stimulators, while showing very limited responsiveness to B10.A(4R) cells. The preferential recognition of determinants on molecules other than Kk or I-Ak was directly proven by isolating 21 T-cell clones, all of which were Ek beta specific. This "dominance" seems to reflect a high frequency of Ek beta reactive T cells in the unselected B10.A(5R) repertoire because: (1) it is already observed in blasts isolated in a primary MLC, (2) it is typical of several independently raised B10.A(5R) anti-B10.A cultures, and (3) it is not found in parallel C57BL/6 anti-B10.BR MLCs that show dominant I-A specificity. Results showing the importance of determinant concentrations expressed by stimulator cells suggest that uncloned T-cell lines are heterogeneous in their "affinities" and that our cloning conditions select cells with high "functional affinity".

Animals↗
PubMed1982

MHC restriction of male-antigen-specific T helper cells collaborating in antibody responses.

By priming female C57BL/6 mice with syngeneic male spleen cells and enriching inguinal and paraaortic lymph node cells in long-term culture (LTC) by repeated restimulations, H-Y-specific T helper cells can be produced. In response to male spleen cells carrying I-Ab antigens these cells activate "antigen-expressing" B cells to secrete polyclonal antibody. Before the end of the second week in LTC it was impossible to detect any helper activity. Induction of plaque-forming cells (PFC) also requires simultaneous recognition of antigen and I-A-encoded determinants in the "stimulator-responder" spleen-cell population. The testing of spleen cells from H-2 recombinant strains as "stimulator-responders" to anti-H-Y helper T cells of C57BL/6 origin also revealed that other genes, telomeric to I-A, control the magnitude of both specific T-cell proliferation and helper-dependent B-cell activation.

Animals↗
PubMed1982

Idiotypic characterization of antibody-induced antibody responses.

Anti-idiotypic antisera were produced in syngeneic (C57BL/6) mice against a monoclonal anti-Dextran B512 (Dex) antibody (38-13). In radioimmunoassays, anti-idiotypic antibodies were shown to react with the homologous idiotype, while failing to recognize another monoclonal anti-Dex antibody, independently derived from C57BL/6 mice (D-16). Plaque inhibition tests confirmed the specificity of the anti-idiotypic antibodies and revealed that the 38-13 idiotype is expressed by about half of all anti-Dex antibodies produced in C57BL/6, but not in CBA mice. Injection of normal (but not athymic) C57BL/6 mice with low doses of 38-13 monoclonal antibodies, contained culture supernatants or ascitic fluids, resulted in a 10-20 fold increase in the numbers of anti-Dex PFC detected in the spleen 5 days later, the majority of which carried the 38-13 idiotype.

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