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A Bandeira

Publications and source records attributed to A Bandeira.

70 records · Page 4Linked to original sources
PubMed1985

Interactions of small B lymphocytes with unprimed noncytolytic T cells: dissociation between "presentation" and growth induction.

The accessory cell requirements in lectin-dependent triggering and growth of unprimed Lyt-2-T lymphocytes were analyzed by quantitatively comparing the ability of small B cells and peritoneal macrophages to either induce reactivity to growth factors or support growth. Lightly or nonirradiated small B cells were 15 to 30-fold less efficient as compared to T cell-depleted peritoneal cell populations, in the support of the lectin-stimulated Lyt-2-T cell proliferation. In contrast, lightly irradiated small B lymphocytes were quantitatively as efficient as macrophages in mediating lectin-driven Lyt-2-T cell proliferation, if relevant supernatants were added into culture. Finally, supernatants derived from cultures where T-small B cell ratios were optimal for growth of responder Lyt-2-lymphocytes were two orders of magnitude less efficient than conditioned medium obtained from cultures containing optimal T-macrophage ratios, in their ability to support growth of activated T cells. We conclude from these experiments that: in contrast to cytolytic T cell precursors, lectin-dependent induction of unprimed Lyt-2- T lymphocytes requires accessory cells; small B cells and macrophages are equally competent in this respect; and growth support by small B cell populations is due to contamination by macrophages which are the only cell type performing this function. We therefore interpret reports on Lyt-2- T cell proliferation upon stimulation with high numbers of small B cells as a two-step process: "presentation" and induction of T cells which is essentially B cell dependent, and factor production ensured by contaminating macrophages.

Animals↗
PubMed1985

Natural effector T lymphocytes in normal mice.

The "natural" T-cell activity in normal unimmunized mice was studied. By double-parameter fluorescence-activated cell sorter analysis, it was found that 5-10% of all splenic Lyt-2+ and L3T4+ lymphocytes are large, of which more than half are in mitotic cycle. In contrast with small resting cells of the same phenotype, activated (large) T cells isolated from normal mice are functional effector cells: L3T4+ large cells induce normal B lymphocytes into proliferation and antibody secretion, while large Lyt-2+ cells efficiently suppress B-lymphocyte responses. No effector cell cytolytic activity could be detected among naturally activated T cells. The significance of these findings for the internal activity in the normal immune system is discussed.

Animals↗
PubMed1985

Functional analysis of pokeweed mitogen-dependent cell interactions in murine spleen cells. I. Lack of B-cell mitogenicity and low frequency of effector helper T cells.

The nature of lymphocyte responses on addition of pokeweed mitogen (PWM) to normal murine spleen cells was studied in low cell density cultures. PWM, over a wide range of concentrations, stimulated proliferation in a set of cells roughly 10-fold smaller than the lymphocyte populations responding to either concanavalin A or lipopolysaccharide. PWM also induced a relatively small number of B lymphocytes in these cultures to mature to Ig-secreting plaque-forming cells (PFC). Proliferative and PFC responses were completely abrogated by T-cell removal from normal spleen cell cultures. Moreover, cell mixture and irradiation experiments demonstrated that B lymphocytes do not proliferate in response to PWM, even in the presence of an excess of normal T cells, suggesting that PFC development results from terminal maturation without proliferation. Finally, parallel titrations of cloned helper cells, normal splenic T cells or T-cell blasts induced by PWM showed that the poor B-lymphocyte responses in normal spleen cell cultures is due to the very low frequency of competent helper cells in these populations. PWM, however, was competent to activate and expand this set of helper lymphocytes in primary cultures.

Animals↗
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

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

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

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↗
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

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↗
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

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↗
PubMedDate not supplied

From the mechanisms of lymphocyte activation to internal activity in the immune system.

The principles of lymphocyte activation were summarized for all three sets of immunocompetent cells: B cells, cytotoxic cells and helper T lymphocytes. They were then used to derive the basic mechanisms and specificities which drive internal activity in the normal immune system and which select available antibody repertoires. It was postulated that "natural antibodies" are induced by "natural helper cells" and are selected on the basis of their idiotypic profiles, which are complementary to available T-helper-cell repertoires. "Natural idiotypes" would then carry idiotopes similar to MHC epitopes, the predominant germ-line specificity of T-cell repertoires.

Animals↗
PubMedDate not supplied

[Apicoectomy].

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Apicoectomy↗