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P Benaroch

Publications and source records attributed to P Benaroch.

7 recordsLinked to original sources
PubMed1992

T cell-induced allotypic suppression. Origin of the CD8+ T cells maintaining IgG2ab suppression.

One of the problems raised by the T cell-induced allotypic suppression is the origin (donor or host) of the T cells responsible for the chronicity of the suppression. To address this point, we used T cells from Igha/a Thy-1.2 mice whose natural T cell activity against IgG2ab was enhanced in vivo. These T cells were injected into newborn Ighb/b Thy-1.1 mice where they induced complete suppression of IgG2ab expression in around 70% of these recipients. During a study that lasted more than 1 yr, we found that about 3% of the recipient splenocytes were T cells of the donor type. By means of suppression-transfer experiments, using either Thy-1.2+ or Thy-1.1+ cell-depleted splenocytes from mice suppressed in this manner we were able to unambiguously show that Thy-1.2+ cell-depleted splenocytes were incapable of transferring the suppression, whereas Thy-1.1+ cell-depleted splenocytes could. We thus demonstrated that suppression was maintained throughout the recipient's life by donor Thy-1.2+ T cells.

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PubMed1992

Tetrameric cell-surface MHC class I molecules.

Purified major histocompatibility complex (MHC) class I molecules have been studied at high resolution by X-ray crystallography; the structure is a complex of a single heavy chain, a beta 2-microglobulin light chain and a tightly bound peptide moiety. We show here that complete MHC class I molecules are post-translationally assembled into tetramers (made up of four heavy chains and four beta 2-microglobulin units) and that this tetrameric species is expressed on the cell surface. The multivalent tetrameric structure of class I molecules can be reconciled with models of T-cell activation that invoke antigen-receptor crosslinking, as opposed to models that depend on an allosteric change.

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PubMed1992

Plasmodium chabaudi and Trypanosoma cruzi infections can reverse IgG2ab chronic suppression in mice.

The effects of infections with Plasmodium chabaudi or Trypanosoma cruzi on chronic CD8+ T cell dependent IgG2ab suppression were analyzed in homozygous Ighb/b adult mice. These parasites are known to induce a CD4+ T cell dependent polyclonal activation characterized in particular by a considerable increase in IgG2a expression. We report here that infection with either parasite reversed the IgG2ab suppression in 18 out of 32 mice. However, in mice treated with anti-CD4 mAb in parallel to the parasite infection, the polyclonal activation was largely reduced and the suppression of IgG2ab expression was always maintained. The parasite induced escape from suppression could result from increased helper T cell activation stimulating some of the Ig production. A weakening of the CD8+ T cell activity which is specific of IgG2ab could also contribute to the IgG2ab production. Both effects would shift the previous equilibrium which was in favour of suppression to a new balance allowing expression of the IgG2ab allotype.

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PubMed1989

T cell-induced Ig allotypic suppression in mice. II. Both CD4+ CD8- and CD4- CD8+ T cell subsets from sensitized Igha mice are required to induce suppression of Igh-1b allotype expression.

We established the phenotype of T splenocytes (Ts) from Igha/a BALB/c mice sensitized against B splenocytes from the Ighb/b CB20 congenic mice that induce Igh-1b (IgG2a of the Ighb haplotype) suppression. This was achieved by studying the action of anti-T cell subset mAb on the capacity of Ts to induce this chronic allotypic suppression in Igha/b (BALB/c x CB20)F1 mice. The Ts were treated with cytotoxic anti-mouse CD4 or anti-mouse CD8 rat mAb in vitro before their injection into the Igha/b newborns or in vivo after their injection into the Igha/b newborns. Exposure to either anti-CD8 or anti-CD4 mAb in vitro or in vivo leads to loss of the capacity of Ts to induce Igh-1b allotypic suppression. Mixing CD4+-cell-depleted Ts and CD8+-cell-depleted Ts preparations restored the capacity of the cells to induce Igh-1b suppression. Thus, both CD4+ CD8- Ts and CD4- CD8+ Ts are required for the induction of this allotypic suppression. Bone marrow cells and B splenocytes from Igh-1b-suppressed adult Igha/b mice were shown to be able to durably express Igh-1b when transferred into irradiated Igha/a BALB/c hosts whereas whole spleen cells from such donors failed to do it. Abrogation of Igh-1b suppression by in vivo anti-CD8 mAb treatment was achieved in adult Igha/b heterozygotes but with a lower efficiency than in adult Ighb/b homozygotes, all being chronically Igh-1b suppressed. The CD4- CD8+ cell population essential for maintaining this suppression is resistant to in vivo 600 rad irradiation and seems to be slightly inhibited by in vivo administration of free Igh-1b.

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PubMed1988

Cellular induction of chronic allotype suppression of IgG2a in Ighb/b homozygous mice and its abrogation by in vivo treatment with anti-CD8 monoclonal antibody.

We report here the successful induction of allotype suppression in homozygous Ighb/b mice (CB20 or C57BL/6) by neonatal injection of T splenocytes from Igha congenic sensitized mice (BALB/c or BC8, respectively). The sensitization of the T cell donors was achieved by two intravenous injections of B splenocytes from Ighb congenic mice. Treated homozygous Ighb/b mice developed, as of 16-24 wk of age, a chronic suppression of Igh-1b expression (IgG2a of Ighb haplotype). The other productions tested (IgM, IgD, and IgA) of Ighb haplotype were unaffected. In vivo treatment with cytotoxic anti-CD4 or anti-CD8 mAb of mice subjected to chronic Igh-1b suppression clearly showed that CD8+ lymphocytes (suppressor or cytotoxic cell) were essential for the maintenance of the suppression. The suppression was indeed abrogated after a 1-wk treatment with anti-CD8 mAb containing culture supernatant, whereas, the anti-CD4-treated mice continued to be subjected to suppression. This anti-CD8 in vivo treatment was shown to have no effect on thymus but to severely reduce the percentages of CD8+ cells in spleen and in peripheral blood without affecting the percentages of CD4+ cells, leading to a large and rapid Igh-1b expression (up to 0.5 mg per ml of serum, the day after the end of the treatment). This suppression abrogation, and thus the Igh-1b expression, was either transient or permanent. When it was transient, a second 1-wk treatment with anti-CD8 mAb containing culture supernatant induced once again a rapid and significant production of Igh-1b (up to 0.3 mg of Igh-1b per ml of serum).

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PubMed1988

Enhancement in Igha mouse strains of the "natural" suppressive activity of normal T splenocytes against the expression of Igh-1b allotype. I. Molecular aspects of the chronic suppression obtained.

Several approaches have been used in our attempts to increase the "natural" ability of normal T splenocytes (Tn) from BALB/c or BC8 mice (both Igha) to induce, in F1 hybrids, a suppression of Igh-1b expression (IgG2a of b haplotype). These heterozygous F1 were produced by mating these Igha mice and their Ighb-congenic partners (CB20 and C57BL/6, respectively). The most powerful approaches were to sensitize the Igha mice by either autologous splenocytes coated with Igh-1b or B splenocytes from Ighb-congenic mice. In F1 having paternally inherited the b haplotype the sensitized T splenocytes (Ts) prepared from such mice are able to induce, like Tn, when injected at birth, a chronic suppression of Igh-1b expression. However, the suppression was established with a much higher efficiency: already at 6 weeks of age in 100% of the F1 treated with 1 x 10(7) Ts, vs. a final rate of 70% progressively reached only at 42 weeks of age in the F1 treated with 4 x 10(7) Tn. In F1 having maternally inherited Ighb the differences were even more pronounced than with 4 x 10(7) Tn, i.e. the suppression induction was almost totally ineffective, whereas with 2 x 10(7)-4 x 10(7) Ts, a rate of 100% treated F1 subjected to suppression was reached at 19 weeks of age. As the productions of IgM, IgD and IgA of the b haplotype were not affected by the suppression, the Ts are believed to act on the Igh-1b+ cells. Attempts were also made to induce allotypic suppression of other b allotypes by the use, as sensitizing cells, of myeloma cells carrying Igh-6b (IgM of b haplotype). We failed in revealing any sign of a T cell reactivity against Igh-6b similar to the reactivity against Igh-1b. The use of Igh-6b+ myeloma cells grown in an Ighb or in an Igha background allowed us to assume that the cells responsible for the sensitization are, in the Ighb B lymphocyte population, either the Igh-1b+ lymphocytes or the lymphocytes having passively adsorbed this allotype, or both.

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