Search PubMed⌕ Search

Biomedical subjects

A Coutinho

Publications and source records attributed to A Coutinho.

At least 235 records · Page 13Linked to original sources
PubMed1984

B lymphocyte activation upon exclusive recognition of major histocompatibility antigens by T helper cells.

This study has investigated whether exclusive recognition of I-A or I-E molecules on the B cell surface by T helper cells is sufficient to activate resting B cells. Lines and clones of long-term-cultured T helper cells with specificity for I-A or I-E antigens have been derived from mixed lymphocyte cultures between spleen cells from major histocompatibility complex (MHC)-congenic mouse strains. These cells were tested for helper activity and proved competent to induce resting B lymphocytes expressing the specific MHC antigens to polyclonal expansion and maturation to Ig secretion. B cell activation was shown to require direct recognition of I-A/E antigens by the helper cells on the responding B lymphocyte surface and it could not be achieved by soluble factors released by "third-party" helper cell activity ongoing in the same cultures. Since B lymphocyte activation occurs in the absence of antigen recognition by the responding B cells, these observations suggest that I-A and I-E molecules expressed on the B cell surface participate in the functional reception of T helper cell-derived induction signals.

Animals↗
PubMed1984

On the role of I-A antigens in lectin- and antigen-induced interleukin 2 production.

The role of I-A molecules in lectin- and antigen-induced interleukin 2 (IL2) production has been analyzed using monoclonal antibodies. Both lectin- and antigen [plus major histocompatibility complex (MHC)]-induced IL2 production were profoundly inhibited by monoclonal anti-I-A antibodies, whereas monoclonal anti-D and anti-K antibodies had no effect. The anti-I-A-mediated inhibition of lectin-induced IL2 production was fully overcome by addition of interleukin 1 (IL 1), while no reconstitution was observed in antigen (plus MHC)-specific induction. Anti-I-A antibodies were also found to inhibit the T cell-independent induction of IL 1 production. I-A antigens appear, therefore, to play two distinct roles in the induction of IL 2 production: (a) I-A molecules are directly involved in mediating activation signals to the macrophages at the level of IL 1 production; (b) I-A epitopes act as restricting elements in specific antigen recognition by T helper cells at the level of IL 2 production, a requirement which is overcome by lectin.

Antibodies, Monoclonal↗
PubMed1984

Reactions among IgM antibodies derived from normal, neonatal mice.

Attempting to obtain a representative sample of the "natural antibody" repertoire in the developing immune system, we have derived IgM-secreting hybridomas from 4 normal untreated BALB/c mice of the same litter on day 6 after birth. Partially purified IgM preparations obtained in the supernatants of 70 such clones were each screened in binding assays for reactivity with a panel of 9 IgM antibodies, randomly selected from the same collection. Five of these 9 IgM antibodies were found to react with a considerable number of other IgM in the collection, while the other 4 showed only sporadic reactivity. On the other hand, more than half of the 70 antibodies were found to bind specifically to at least one of these five. With a few exceptions, these reactions showed quantitative levels ranging from 5 to 20% of those observed between either of the two interacting IgM and monoclonal rat anti-mu antibodies. The selectivity of these reactions indicated V-region specificity, which was confirmed by analyzing in some detail the reaction between 2 IgM antibodies isolated from the same mouse.

Animals↗
PubMed1984

Activation and growth requirements for cytotoxic and noncytotoxic T lymphocytes.

The number and nature of the "signals" required for lymphocyte activation have been so repetitively and academically discussed over the last 15 years that both the readers and the authors appear exhausted by such exercises. Yet, what may be considered to be the essential question, the basis for self-nonself discrimination, remains to be clarified. Since it has been established that clonal expansion and maturation to effector functions are brought about by polyclonally ("immunologically nonspecific") active factors, it is obvious that the crucial "step" in this context is the initial interaction of antigen with specific receptors of immunocompetent lymphocytes. This initial discriminatory event appears to proceed differently on the various cell subsets. We first deal with the mechanism of induction and growth of cytotoxic-T-lymphocyte precursors, and then discuss the inductive requirements leading to proliferation of T helper cells.

Antigens, Surface↗
PubMed1984

Idiotypic determinants of natural IgM antibodies that resemble self Ia antigens.

A collection of immunoglobulin-secreting B-cell hybridomas was derived from normal neonatal BALB/c spleen and searched for reactivity against a panel of monoclonal anti-H-2 antibodies. We describe here one IgM antibody which was found to react with the monoclonal anti-Ia.7 antibody 14-4-4S. The characterization of this clone (BA.N 4:4.57) revealed its anti-trinitrophenyl specificity and demonstrated specific binding to five different monoclonal anti-Ia.7 antibodies but not to other anti-H-2 antibodies. The variable region specificity of these interactions was shown by the use of pepsin Fab fragments of the IgM antibody. Anti-Ia.7 antibodies were shown to specifically inhibit plaque formation by the hybridoma cells, and dinitrophenylglycine was shown to inhibit the reaction between the IgM antibody and anti-Ia.7 molecules. We interpret these results as to indicate that BA.N 4:4.57 expresses an idiotope or idiotopes which mimic Ia.7 determinants. This idiotypic family is naturally expressed in both newborn and adult BALB/c mice, as shown by the presence in normal serum of IgM molecules that specifically react with the F(ab')2 fragment of the 14-4-4S antibody. We speculate on the importance of idiotypic mimicry with major histocompatibility complex determinants, for both the selection of natural antibody repertoires and the evolution of antibody genes.

Animals↗
PubMed1984

Internal complementarities in the immune system: regulation of the expression of helper T-cell idiotypes.

More than half of BALB/c helper T lymphocytes specific for 2,4,6-trinitrophenyl (TNP)-modified syngeneic spleen cells are inhibited in their proliferative responses to antigen-presenting cells and in their cooperation with B lymphocytes by monoclonal anti-idiotypic antibodies directed to a TNP-binding BALB/c myeloma protein (MOPC 460). This inhibition is specific for anti-TNP-self helper cells of BALB/c origin and is controlled by IgCh-linked genes, as it is not observed with CB.20 helper cells of the same specificity. In contrast, anti-TNP-self helper cells prepared from BALB/c mice that were chronically suppressed with anti-mu chain antibodies and possessed no B lymphocytes were not inhibited by anti-idiotypic antibodies. We conclude that the B-cell antibody repertoires contribute to the selection of the (idiotypic) T-helper-cell repertoires.

Animals↗
PubMed1984

Functional and chemical characterization of B-cell growth factor produced by normal cloned T helper cells.

Media conditioned by clones of normal helper T cells exposed to appropriate antigen-presenting cells contain growth-promoting activity for B-cell blasts induced either by lipopolysaccharide or on direct interaction with competent helper cells. This B-cell growth factor (TH-BGAPet) is recovered on sodium doecyl sulphate polyacrylamide gel electrophoresis corresponding to mol. wt of 15,000-20,000 displays no mitogenicity for small, non-induced B lymphocytes and is completely devoid of the ability to activate immunoglobulin secretion in proliferating B cells. These results are ascribed to the activity derived from normal T cells, with the same characteristics as BSF-p1 previously obtained from lymphomas and hybridomas. Since hybridization of these T helper cells results in the constitutive production of BSF-p1 in the absence of macrophages, these experiments demonstrate that BSF-p1 is a normal T-cell product.

Animals↗
PubMed1984

A quantitative assay detecting small numbers of effector helper T cells, regardless of clonal specificity.

We have developed a new assay for quantitative detection of all helper T cells that can induce normal B lymphocytes to proliferation and Ig secretion. To establish the optimal assay conditions, we have used cloned T helper cells of defined specificities that had previously been shown to activate normal B lymphocytes expressing the specific antigen(s) on direct cellular interactions. As shown in this paper, 'irrelevant' B lymphocytes--that is, those that do not express either antigen or restriction elements recognized by the effector helper T cells--can also be induced in the presence of appropriate concentrations of pokeweed mitogen which are not mitogenic for the 'target' B lymphocytes. 'Nonspecific' plaque-forming cell responses are of the same magnitude as those provided to specifically triggered targets and equal or better than those induced by lipopolysaccharide. The assay is highly sensitive and enables 'semi-quantitative' detection of less than 20-30 effector T cells per culture. Since effector helper T cells can be detected regardless of the clonal specificity, the assay appears useful for quantitative studies of various populations of T helper cells displaying mixed specificities and for the classification of cells with unknown functions.

Animals↗
PubMed1984

T cell-dependent B cell activation.

T cell-dependent induction of small, resting B lymphocytes requires direct recognition of antigen and/or I-A/E molecules on the B cell surface by the inducing helper cell, and it does not require the participation of Ig receptors on the responding B cell. Triggering B cell receptors, therefore, are either the I-A/E molecules themselves, or other structures with complementarities on helper cell membranes that become available for productive interactions upon I-A/E recognition. It would appear that signal delivery by such triggering receptors can be regulated by a membrane complex of molecules, involving immunoglobulins, Class II MHC molecules and other classes of receptors, which in selective and distinct manners control the quantitative levels of expression and/or availability of the relevant structures. Classical in vivo observations and our in vitro experiments led us to conclude that induction of B cells does not occur upon binding of T cell-dependent antigens to Ig receptors and, consequently, that B lymphocyte activation by anti-receptor antibodies has no physiological counterpart. Induced B lymphocytes proliferate and mature to high rate secretion of antibodies under the influence of selective growth and maturation factors produced by helper cells which are MHC-unrelated, act polyclonally and have no influence in normal, resting cells. Specific ligand interactions with the membrane molecules participating of that functional complex may also regulate reactivity to either growth or maturation factors, and, thus, control clonal performances and the fate of activated cells.

Animals↗
PubMed1984

The immune response to bacterial dextrans. IV. Antibody idiotypes.

Anti-idiotypic antisera (a-Id) were prepared in SJL mice against the dextran B512 (Dex)-specific hybridoma antibody D.16.6 (mu, kappa) of C57BL/6 origin. Such a-Id were specific for the D.16.6 antibody, but the idiotypic determinants recognized were not hapten modifiable. The a-Id were used in radioimmunoassays (RIA) to study the genetic control of the expression of the D.16.6 idiotype (Id) in a variety of mouse strains. It was found that all mouse strains tested expressed this Id as a component of the normal background immunoglobulin (Ig) in their sera. Only in mice of the IgCHb haplotype, however, was the Id found in association with Dex-specific antibodies. Furthermore, even in IgCHb mouse strains, not all individuals expressed Id-positive anti-Dex antibodies. Because the D.16.6 Id is a "recurrent" natural Id, but a "non-dominant" Id in the Dex response of IgCHb mouse strains, these observations contradict our previous suggestions on the selection of "dominant" Id from the pool of "naturally" produced Ig.

Animals↗
PubMed1984

The role of I-A/E molecules in B lymphocyte activation. I. Inhibition of lipopolysaccharide-induced responses by monoclonal antibodies.

A panel of 22 different monoclonal antibodies, including specificities against various antigenic clusters of I-A and I-E molecules, were probed over a wide range of concentrations for their ability to inhibit lipopolysaccharide-induced B lymphocyte proliferation and maturation to immunoglobulin-secreting plaque-forming cells (PFC). Most antibodies were competent to inhibit up to 80 to 100% of the response of appropriate target cells, although having little or no effect on irrelevant spleen cell cultures. Mixtures of either anti-I-A or anti-I-E specificities were more efficient inhibitors than individual antibodies, as shown by the average concentrations required for 50% inhibition (30 and 300 ng/ml, respectively). The selective role of I-A/E molecules in B cell activation was demonstrated by the failure of anti-K antibodies of the same isotype, bound in comparable amounts to target cells, to modulate B cell responses in parallel cultures. Fc receptor-mediated inhibitory effects were further excluded by equivalent inhibition obtained with anti-I-A antibodies of the IgM class. Anti-I-A/E antibodies appear to inhibit the inductive phase of B cell responses, as suggested by limiting dilution experiments performed in the presence of 50% inhibitory concentrations of antibodies: 50% of the control number of reactive clones were found to respond, but those that escaped inhibition developed to control sizes of progenies producing PFC.

Animals↗
PubMed1983

Immune response to bacterial dextrans. II. T cell control of antibody isotypes.

The isotype distribution of Dextran B 512 (Dex)-specific plaque-forming cells (PFC) and serum antibodies was studied after in vivo immunization in C57BL/6 mice. Although IgG2b and IgG3 could also be detected in most individuals, the majority of non-IgM PFC were of the IgA isotype. All classes other than IgM were T cell-dependent, as shown by their complete absence in athymic "nude" mice. This unusual isotype pattern was further investigated by studying the antibody responses to the same Dex epitope coupled to a protein carrier, and to a different hapten coupled to the carrier Dex or to a protein. The results show that IgA responses are epitope-related and selectively associated with anti-Dex antibodies: no IgA PFC are detected against a hapten coupled to Dex or proteins, while the enhanced levels of helper cell reactivity provided by protein carrier to Dex result in the appearance of IgG1 antibodies in addition to IgA. These results indicate that T cells that modulate isotype patterns in these responses can discriminate between Dex- and DNP-specific B cells in the response to the same carrier. Since the same idiotype is detected on a large fraction of the IgM and IgA anti-Dex response and antiidiotypic helper cells have previously been detected in normal C57BL/6 mice, we suggest that idiotype-specific T cells control the production of IgA antibodies upon immunization with Dex.

Animals↗
PubMed1983

Differential macrophage requirements for T helper cell and T helper cell-induced B lymphocyte proliferation.

Major histocompatibility complex-restricted helper T cell clones against "minor" antigens expressed on B cell and macrophage surfaces, when confronted with appropriate T cell-depleted spleen cells, are induced to proliferation and, in turn, activate "target-responder" B cells to polyclonal growth and maturation. Irradiation of helper cell populations, however, demonstrates that their effector functions (and B lymphocyte responses) are independent of proliferative activity. Adherent cell depletion on Sephadex G10 columns, while completely abrogating helper T cell proliferation, does not abolish helper cell-induced B cell responses, demonstrating a remarkable quantitative difference in macrophage requirements for the growth of these two cell types. Because significant B cell responses are detected upon interaction with primed helper T cells under conditions of extreme macrophage depletion, we conclude that the role of macrophages in T-B cell cooperation is limited to expansion of optimal numbers of helper T lymphocytes. It follows that activated helper cells can autonomously produce all B cell-specific growth and maturation factors mediating cooperative antibody responses. In contrast, the profound reduction of LPS-induced responses upon macrophage depletion suggests accessory cell production of such factors in thymus-independent B cell growth and/or maturation.

Animals↗
PubMed1983

Isotype commitment in the in vivo immune responses. II. Polyclonal plaque-forming cell responses to lipopolysaccharide in the spleen and bone marrow.

Injection of lipopolysaccharide into adult mice results in a rapid increase in the number of splenic IgM-secreting plaque-forming cells (PFC) so that by 60 h they represent roughly 20 times those present in normal mice. Although inhibited for the first two days, IgG3, IgG2b and IgG2a PFC are later selectively stimulated and, by 110 h, they reach numbers that are 100, 40 and 30 times, respectively, those of normal mice. IgG1 PFC are stimulated only marginally and 48 h after the maximal responses of the other IgG subclasses. IgA PFC are selectively inhibited and drop to 20% of normal numbers 4 days after injection. The ability of lipopolysaccharide to selectively stimulate B cells for the production of IgG3, IgG2b and IgG2a was further substantiated by studying athymic mice, and by using adoptive cell transfers that overcome regulatory influences limiting these responses in intact mice. Under these conditions, 16% of all spleen cells are PFC and up to 85% of all Ig-secreting cells are included in those three isotypes. Similar responses are also detected in bone marrow but they occur 24-48 h after the splenic responses, suggesting that bone marrow PFC are not induced in situ. These results demonstrate a selective in vivo isotype commitment in response to lipopolysaccharide that is polyclonal and, therefore, independent of V region specificities.

Animals↗
PubMed1983

An example of major histocompatibility complex-linked control of idiotypic interactions.

Normal euthymic mice, injected i.v. with low doses of syngeneic monoclonal antibodies carrying "recurrent" idiotypes, develop a specific increase in numbers of splenic IgM plaque-forming cells that are paratopically and idiotypically similar to the injected antibody. We have now studied the responsiveness to a C57BL/6 anti-dextran a(1 leads to 6) and BALB/c anti-TNP (trinitrophenyl) monoclonal antibodies in a variety of strains. It was found that such responses are controlled by two linkage groups, namely major histocompatibility complex (MHC) and Ig-1.

Animals↗
PubMed1983

Distinct helper activities control growth or maturation of B lymphocytes.

A clone (C-11) of C3H/HeJ Lyt-1+2-T cells with specificity for "minor" antigens of C3H/Tif has been isolated which, in contrast to other similarly derived clones, did not activate polyclonal plaque-forming cell (PFC) responses in T cell-depleted "target" spleen cells. This clone, however, showed unaltered proliferative responses to the naturally occurring antigen(s) on presenting cells, and strongly synergized with regular helper clones in the induction of PFC responses. Further analysis demonstrated that C-11 cells are competent to stimulate extensive "target" B cell proliferation, but lack the ability to produce (or participate in the production of) maturation factors for activated B cells. Thus, the defective PFC responses could be fully reconstituted with supernatants from regular clones stimulated with antigen, but not by supernatants prepared from the C-11 cells themselves. While it is not clear whether this clone represents a normal helper T cell subpopulation or a variant that has lost maturation-factor production, these results demonstrate that distinct factors control growth and maturation in T cell-dependent B lymphocyte responses.

Animals↗