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B Benacerraf

Publications and source records attributed to B Benacerraf.

At least 55 records · Page 3Linked to original sources
PubMed1991

Dissociation of beta 2-microglobulin leads to the accumulation of a substantial pool of inactive class I MHC heavy chains on the cell surface.

A large pool of free class I heavy chains is detected in situ on the plasma membrane of living cells. These chains are present on cells of different MHC genotypes and appear to exist under physiological conditions in vivo. These molecules arise from the dissociation of previously assembled class I heterodimers at the cell surface. The ratio of intact to dissociated heterodimers is strongly affected by the occupancy of the peptide-binding site of the class I molecule. Upon dissociation of the heterodimer, the class I molecule is functionally inactive. These findings may help to explain why class I molecules on the cell surface are unreceptive to binding peptides yet readily associate with peptides in the presence of exogenous beta 2-microglobulin. These results have implications for understanding the distinct functions of class I versus class II molecules and how the immunological identity of cells is preserved.

Animals↗
PubMed1991

Low temperature and peptides favor the formation of class I heterodimers on RMA-S cells at the cell surface.

RMA-S murine cells have a mutation that interferes with the assembly of class I major histocompatibility complex (MHC) heterodimers and are deficient in the expression of class I molecules on the cell surface. The mutant phenotype has been reported to be normalized upon incubation of RMA-S cells at 25 degrees C. We find that much of the increased expression of class I heterodimers is dependent on culturing RMA-S cells in bovine serum or with purified bovine beta 2-microglobulin. Furthermore, epitopes that are associated with class I MHC molecules that have bound xenogeneic beta 2-microglobulin are preferentially formed on RMA-S cells cultured at 25 degrees C. These heterologous class I molecules are thermolabile. Increased expression of class I molecules has also been observed on RMA-S cells incubated at 37 degrees C in the presence of class I-restricted peptides. We find that the increased expression of Db molecules induced by influenza virus nucleoprotein residues 365-380 is similarly dependent on culturing RMA-S cells in bovine serum or with purified bovine beta 2-microglobulin.

Animals↗
PubMed1991

Weak base amines can inhibit class I MHC-restricted antigen presentation.

This report describes the effects of NH4Cl, CH3NH2, and chloroquine on class I and II MHC-restricted Ag presentation. OVA-specific T-T hybridomas were used to detect processed OVA in association with class I, H-2Kb, and class II, I-Ad/b, molecules on a B lymphoblastoid APC. OVA, internalized by APC under hypertonic conditions, was presented in association with class I and II MHC molecules. Treating the APC with NH4Cl or CH3NH2 inhibited class I- and II-restricted Ag presentation. In contrast, chloroquine markedly inhibited class II, but not class I-restricted Ag presentation. Controls indicated that drug-treated APC were fully competent to interact with T cells and present processing-independent antigenic peptides in association with both class I and II MHC molecules. NH4Cl and CH3NH2 did not inhibit the uptake of radiolabeled Ag by the APC. After the proteolytic removal of H-2Kb from the surface of APC, NH4Cl and CH3NH2-treated and control APC regenerated identical amounts of surface H-2Kb and this regeneration required de novo protein synthesis. These latter results indicate that NH4Cl and CH3NH2 can inhibit Ag presentation without affecting the synthesis, transport, or surface expression of H-2Kb. Also, NH4Cl did not affect the transport of H-2Db to the surface of mutant RMA-S cells that were cultured with exogenous peptides. Taken together these results strongly suggest that NH4Cl and CH3NH2 but not chloroquine can inhibit a critical and early intracellular step in class I-restricted Ag presentation while simultaneously inhibiting class II-restricted Ag presentation.

Amines↗
PubMed1991

Reassociation with beta 2-microglobulin is necessary for Db class I major histocompatibility complex binding of an exogenous influenza peptide.

A synthetic peptide corresponding to residues 365-380 of the influenza nucleoprotein (NP365-380) has been previously shown to associate with class I major histocompatibility complex-encoded molecules and to stimulate cytotoxic T lymphocytes [Townsend, A. R. M., Rothbard, J., Gotch, F. M., Bahadur, G., Wraith, D. & McMichael, A. J. (1986) Cell 44, 959-968]. We find that intact Db class I heterodimers on the cell surface are unreceptive to binding this antigen. However, NP365-380 readily associates with Db molecules on the plasma membrane in the presence of exogenous beta 2-microglobulin. In addition, there is a second pathway through which this peptide associates with class I molecules that requires energy and de novo protein synthesis. These findings have implications for maintaining the immunological identity of cells and for the use of peptides as vaccines for priming cytolytic T-cell immunity.

Animals↗
PubMed1991

When all is said and done....

Dr. Benacerraf describes his experience in training immunologists for a period of over 30 years. He then analyzes the circumstances in which selected discoveries were made in his laboratory and the events and reasoning that led to these findings. The following topics are discussed: The phagocytic activity of the reticulo-endothelial system. The pathogenesis of immune complex diseases. The impact of activated macrophages on tumor rejection. The evidence that T-cell immunity is specific for internal protein determinants generated by antigen processing. The maturation of the antibody response in terms of antibody affinity. The discovery of Ir gene control of specific immune responses and the role of MHC molecules as presenters of peptide antigens to T cells. The generation of alloreactivity. Lastly, he addresses the administration of science and, particularly, the problems related to the transfer of technology to industrial partners.

Allergy and Immunology↗
PubMed1990

Reassociation with beta 2-microglobulin is necessary for Kb class I major histocompatibility complex binding of exogenous peptides.

T lymphocytes recognize endogenously produced antigenic peptides in association with major histocompatibility complex (MHC)-encoded molecules. Peptides from the extracellular fluid can be displayed in association with class I and class II MHC molecules. Here we report that mature Kb class I MHC molecules bind peptides upon dissociation and reassociation of their light chain. Intact Kb heterodimers, unlike class II MHC molecules, are relatively unreceptive to binding peptides. This property may maintain segregation of class I and class II MHC-restricted peptides and has implications for the use of peptides as vaccines.

Animals↗
PubMed1989

A randomized, placebo-controlled, double-blind study evaluating the efficacy of leuprolide acetate depot in the treatment of uterine leiomyomata.

Thirty-eight premenopausal women with uterine leiomyomata were enrolled in a randomized, double-blind, placebo-controlled study evaluating the efficacy of depot leuprolide acetate (LA), a gonadotropin-releasing hormone agonist, in decreasing uterine volume. Eighteen women received intramuscular (IM) depot LA 3.75 mg every 4 weeks for 24 weeks (group A); 20 women received IM placebo with the same injection schedule (group B). Group A patients had a mean reduction in pretreatment uterine volume from 505 +/- 93 cu cm (mean +/- standard error of the mean) to 305 +/- 57 cu cm after 12 weeks (P less than 0.05 versus pretreatment) and 307 +/- 57 cu cm after 24 weeks of therapy (P less than 0.05 versus therapy (P less than 0.05 versus pretreatment). At 3 months after cessation of therapy, the mean uterine volume in group A had increased to 446 +/- 92 cu cm (P less than 0.05 versus week 24). Group B patients had no significant change in uterine volume over the 24-week treatment period. These results suggest that depot LA therapy may significantly decrease uterine volume in patients with leiomyomata, but that regrowth of uterine size occurs shortly after cessation of therapy.

Adult↗
PubMed1989

Costimulatory signal provided by a B-lymphoblastoid cell line and its Ia-negative variant.

We have analyzed the requirements of highly purified, resting murine CD4+ T lymphocytes for activation mediated by the lectin Con A and by monoclonal antibodies against the CD3 and Thy-1 molecules. Our results indicate that both the Ia-positive B-lymphoblastoid cell line M12 and its Ia-negative variant M12.C3 can provide the costimulatory activity necessary for these activation pathways. The costimulatory function is preserved upon fixation with paraformaldehyde, indicating that the costimulatory molecule(s) is (are) constitutively expressed on the cell surface. Our experiments also point to interesting differences between the M12 cell line and syngeneic Ia-positive antigen-presenting cells in generating a syngeneic mixed lymphocyte reaction. Finally, we show that the CD4+ T cell-M12.C3 cell interaction can be used to screen for interesting monoclonal antibodies that affect cell function.

Animals↗
PubMed1989

Two genetically identical antigen-presenting cell clones display heterogeneity in antigen processing.

Evidence from various antigen systems suggests that antigen processing can be one factor that determines the repertoire of immunogenic peptides. Thus, processing events may account for some of the disparity between the available and expressed helper T-cell repertoires. In this report, we demonstrate that the immunodominant T-cell determinant in ovalbumin [p323-339; ovalbumin-(323-339) heptadecapeptide] is processed differently by two genetically identical antigen-presenting cell lines, M12 and A20. The ovalbumin-specific T-cell-T-cell hybridomas, DO-11.10 and 3DO-54.8, were used to detect processed antigen. These T-T hybridomas have different fine specificities for the p323-339 determinant. A20 cells presented native ovalbumin well to both T-T hybridomas, whereas M12 cells presented native ovalbumin well to 3DO-54.8 but very inefficiently to DO-11.10. M12 and A20 cells effectively stimulated both T-T hybridomas with the same concentrations of the immunogenic synthetic peptide p323-339. Therefore, M12 cells and DO-11.10 can interact with each other, and both T-T hybridomas have similar sensitivities for the same immunogenic peptide. We conclude that genetically identical antigen-presenting cells can display heterogeneity in the fine processing of an immunodominant T-cell determinant, and synthetic model peptides that represent the minimal stimulatory sequence of a T-cell determinant are not necessarily identical to the structure of in vivo processed antigen. Heterogeneity in antigen processing by individual antigen-presenting cells would serve to increase the repertoire of immunogenic peptides that are presented to T cells.

Animals↗
PubMed1988

The role of antigen-presenting B cells in T cell priming in vivo. Studies of B cell-deficient mice.

Mice rendered B cell deficient by treatment with rabbit anti-mouse IgM (anti-mu) antibodies from birth fail to respond when primed with soluble protein antigens in CFA, as measured by T cell proliferation when challenged with antigen in vitro. The role of B cells in T cell priming in vivo was examined by adoptively transferring hapten-specific B cells into anti-mu mice, followed by immunization with haptenated Ag in CFA. The T cell proliferative response to OVA of anti-mu BALB/c mice was partially restored by the administration of TNP or FITC-specific B cells and immunization with TNP-OVA or FITC-OVA, respectively. This reconstitution was Ag-specific, inasmuch as hapten-binding B cells restored the T cell responses to OVA in mice immunized with the same hapten coupled to OVA. The mechanism of B cell reconstitution of T cell priming in anti-mu mice was addressed using parental to F1 B cell transfers. The Ia restriction pattern of the activated T cells from these mice indicated that both direct presentation of Ag by transferred B cells and antibody-mediated enhancement of Ag presentation by non-B, host Ag-presenting cells occurred. Thus, Ag-specific B lymphocytes play a critical role in priming of T cells in vivo.

Animals↗
PubMed1988

Effects of in vivo monoclonal anti-I-A antibody treatment in neonatal mice on intrathymic and peripheral class II antigen expression.

Intrathymic, Ia-bearing antigen-presenting cells (APC) are believed to play an important role in the development of a mature, functional T-cell repertoire. We used chronic in vivo treatment of neonatal mice with anti-I-A monoclonal Ab (MAb) to examine the expression of I-A and I-E antigens on intrathymic and peripheral APC. Three weeks after continuous treatment with anti-I-A MAb, FACS analysis of unfractionated spleen cells revealed a 75-90% reduction in the number of I-A bearing cells. Splenic antigen-presenting capacity measured by the ability of unseparated or density gradient-enriched APC to stimulate I-A- or I-E-reactive T-cell hybridomas was also greatly reduced. In contrast to the expression of I-A and I-E molecules in the splenic APC, anti-I-A MAb treatment resulted in decreased thymic APC I-A expression without significant changes in I-E as measured by FACS analysis. This was confirmed in functional studies in which allo-I-A- or auto-I-A-reactive T-cell hybridomas could not be stimulated by treated thymic APC. Unlike splenic APC, anti-I-A-treated thymic APC did not differ significantly from normals in their ability to stimulate allo-I-E-reactive T hybridomas. This lack of linkage or comodulation of I-A and I-E expression on thymic but not splenic APC may allow us to study the role of I-A molecules and I-E molecules on the development and expansion of functional, mature T-cell repertoires.

Animals↗
PubMed1988

Cloning and expression of a cDNA for the T-cell-activating protein TAP.

The T-cell-activating protein TAP is a murine phosphatidylinositol-anchored glycoprotein whose expression is controlled by the Ly-6 locus. Previous studies have suggested an important role for this protein in physiological T-cell activation. Using oligonucleotide probes, we have now isolated a cDNA clone whose predicted sequence would encode a protein with an NH2-terminal sequence identical to that of the TAP molecule. Further analysis of the predicted protein sequence revealed a cysteine-rich protein with a hydrophobic domain at the COOH terminus and without N-linked glycosylation sites--all features consistent with our previous analysis of the TAP protein. In Southern blot analysis, the Ly-6.2 cDNA clone detects a multigene family and a restriction fragment length polymorphism that maps precisely to the Ly-6 locus. Expression of the cDNA clone in COS cells demonstrates that it codes for TAP and clarifies the relationship between the epitopes recognized by various alpha Ly-6 monoclonal antibodies. Finally, we have studied the expression of Ly-6 mRNA in a variety of cell lineages. Ly-6 transcripts were detected in all organs examined, including spleen, kidney, lung, brain, and heart. This demonstrates that the Ly-6 locus is transcriptionally active in a wide range of organs and suggests that the role of TAP or TAP-like proteins might extend to other tissues.

Amino Acid Sequence↗
PubMed1988

Suppressor T cells, immunoglobulin and Igh restriction.

Why do some T cell express idiotypes that are serologically similar to those of the B cells, since it is now well established that T cells do not use Ig genes for their antigen specific receptors? In this review article, we have summarized some the evidence for the influence of Igh linked genes on the Suppressor T cell repertoire, using anti-u treated mice as a model system. We investigated whether B cells and Ig molecules play a role in the generation of Ts repertoire. While our results clearly confirmed that B cells and Ig are important in the establishment of Ts repertoire, our experiments failed to resolve the fundamental question - 'what dictates the Igh restriction specificity of Ts?' Ts cells from anti-u treated mice did not lose all Igh restriction specificity. Instead, they expressed an altered restriction specificity. These results suggest that there are at least two independent mechanisms responsible for the generation of the suppressor T cell repertoire. A pre-selected germ line one, which is Ig independent, and a mature one, which is Ig dependent. The precise mechanisms responsible for the generation of germ line Ts repertoire remain to be determined.

Animals↗
PubMed1988

Echocardiographic diagnosis of fetal heart defects in mid trimester.

One hundred and thirty five consecutive fetuses of between 16 and 23 weeks' gestation that were considered to be at high risk of having structural heart defects were examined prospectively to determine the reliability of echocardiography for diagnosing such defects in mid trimester. Each echocardiogram was done in a standard manner and cardiac anatomy was analysed segmentally. Twelve fetuses were excluded from analysis because of lack of follow up. Of the remaining 123 fetuses, 109 had no evidence of heart disease when followed up. In this group the prenatal echocardiogram was normal in 105 and technically inadequate in four; thus there were no false positive diagnoses of heart disease in fetuses subsequently shown to have normal hearts. Fourteen had heart defects at follow up. The serious defect was correctly diagnosed prenatally in 10 of 14 cases, whereas in the other four the prenatal echocardiogram was considered normal. Some errors were made in diagnosing associated segmental defects particularly if the heart disease was complicated. Therapeutic abortion was carried out in seven cases; in five of the fetuses the prenatally diagnosed heart defect was the sole or an important contributing reason for the abortion. We conclude that echocardiography is a reliable method for diagnosing many heart defects in the mid trimester.

Echocardiography↗