An unusual outcome for fetus with gastroschisis.
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Abdominal Muscles↗
Biomedical subjects
B Benacerraf
Publications and source records attributed to B Benacerraf.
Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins.
The purpose of this study was to evaluate the relationship between the number of yolk sacs and amnionicity in monochorionic twin pregnancies scanned early in the first trimester. We retrospectively reviewed images of all monochorionic twins scanned between 6 and 9.5 weeks' gestation and with pathologic or sonographic confirmation of chorionicity-amnionicity. Each film was reviewed for the number of yolk sacs present, as well as for the gestational age at which the amniotic membrane was first visualized. Twenty monochorionic-diamniotic pregnancies and two monochorionic-monoamniotic pregnancies met the criteria for inclusion in the study. In diamniotic pregnancies scanned at less than 8 weeks' gestation, only the yolk sacs were identified; none of the dividing amniotic membranes were detected. Two yolk sacs were identified in all but one case. In this case, although one yolk sac was seen at 6 weeks, follow-up scanning at 8 weeks revealed two yolk sacs. In each of the monochorionic-monoamniotic twin pregnancies, one yolk sac was seen at 9 weeks and a single amnion encircled both embryos. We conclude that the sonographic identification of two yolk scas in monochorionic twins enables us to make the diagnosis of diamniotic twins early in the first trimester, before the amniotic membrane can be imaged. The presence of one yolk sac should prompt a follow-up ultrasonogram to assign amnionicity definitively.
Adult↗
The ultrasonographic appearance and outcome for fetuses with masses distorting the fetal face.
Our objective was to determine the appearance, cause, and outcome of fetal face masses diagnosed antenatally by ultrasonography. Over a 6 year period, 10 consecutive fetuses with facial masses were identified. Ultrasonographic findings, neonatal pathologic findings, and outcome data were correlated. Four (40%) of the 10 fetuses died, including one with a palatal teratoma associated with a Dandy-Walker malformation and three with intracranial teratomas--one of which was associated with hydrops fetalis. Among the survivors, one fetus had a dacryocystocele that was managed conservatively and one had drainage of a salivary gland cyst. The remaining four neonates had successful excision of their tumors in the neonatal period and survived; these infants had a nasal teratoma, a thyroid teratoma, a gingival granular cell tumor, and a scalp hemangioma. Four of the 10 pregnancies had associated polyhydramnios, three of which ended in stillbirth or neonatal death. In conclusion, 40% of the fetuses with antenatal diagnosis of fetal facial masses did not survive. If those with intracranial teratomas are removed from this group, one of seven (14%) fetuses with extracranial masses died. The intracranial teratomas were uniformly fatal. Polyhydramnios was associated with poor outcome.
Facial Neoplasms↗
Specific T-cell tolerance may be preceded by a primary response.
We have evaluated the ability of ovalbumin to induce T-cell-specific tolerance in SJL mice. A significant decrease of interleukin 2 in lymph-node culture supernatants from tolerant mice upon antigen stimulation was seen. Oral tolerization was less effective than i.p.- or s.c.-tolerization protocols. Transfer experiments of either splenic or lymph-node T cells from tolerant mice to naive mice definitely ruled out suppression as a mechanism involved in tolerant mice. Surprisingly, we found that, before the establishment of specific T-cell tolerance to ovalbumin, T cells from mice that will display tolerance were responsive and synthesized interleukin 2 upon antigen challenge in vitro. Thus, we concluded that anergy cannot account solely for the T-cell unresponsiveness in tolerant mice. Furthermore, although we cannot rule out the hypothesis that the T-cell unresponsiveness in tolerant mice can be explained by programmed cell death of ovalbumin-specific T cells, these data led us to speculate that T-cell "refractoriness" could explain the drop of interleukin 2 production in lymph-node T-cell culture supernatant from tolerant mice.
Adjuvants, Immunologic↗
Efficient major histocompatibility complex class I presentation of exogenous antigen upon phagocytosis by macrophages.
Antigens in extracellular fluids can be processed and presented with major histocompatibility complex (MHC) class I molecules by a subset of antigen presenting cells (APCs). Chicken egg ovalbumin (Ova) linked to beads was presented with MHC class I molecules by these cells up to 10(4)-fold more efficiently than soluble Ova. This enhanced presentation was observed with covalently or noncovalently linked Ova and with beads of different compositions. A key parameter in the activity of these conjugates was the size of the beads. The APC that is responsible for this form of presentation is a macrophage. These cells internalize the antigen constructs through phagocytosis, since cytochalasin B inhibited presentation. Processing of the antigen and association with MHC class I molecules appears to occur intracellularly as presentation was observed under conditions where there was no detectable release of peptides into the extracellular fluids. When injected in vivo in C57BL/6 mice, Ova-beads, but not soluble Ova, primed CD4- CD8+ cytotoxic T lymphocytes (CTLs). Similar results were obtained in BALB/c mice immunized with beta-galactosidase-beads. The implications of these findings for development of nonliving vaccines that stimulate CTL immunity are discussed.
Animals↗
A mutant antigen-presenting cell defective in antigen presentation expresses class II MHC molecules with an altered conformation.
Ag presentation by APC to class II MHC-restricted T cells involves a sequence of events: 1) intracellular processing of protein Ag into immunogenic peptides, 2) specific binding of peptides to class II MHC molecules, and then 3) transport of the MHC-peptide complexes to the plasma membrane. The critical event in the activation of T cells by APC is the recognition of MHC-associated antigenic determinants by the TCR/CD3 complex. In this report we describe the isolation and characterization of a mutant APC with a defect in an intracellular process that results in its inability to form MHC-peptide complexes for recognition by T cells. The mutant APC cannot present many different protein Ag with both I-A and I-E molecules but is able to present processing-independent peptides. The functional defect in the mutant APC is not caused by either a decrease in expression or a structural mutation in class II MHC molecules. Further, there is no mutation in the invariant chain (li) and it displays a normal kinetics of association and dissociation from the class II MHC molecules during biosynthesis. Although the mutation is not in the genes encoding for the class II MHC molecules or li, the mutant APC expresses class II MHC molecules with distinct serological epitopes suggestive of an altered conformation. Pulse-chase experiments suggest that a conformational difference between I-Ad molecules of wild-type and mutant cells occurs after the class II molecules exit from the endoplasmic reticulum but while they are still associated with li. The mutant cell produces few compact (SDS-resistant) class II heterodimers. This mutant APC provides a tool for studying the cell biology of Ag processing and presentation.
Animals↗
Effects of cyclosporin A, FK 506, and mycalamide A on the activation of murine CD4+ T cells by the murine B7 antigen.
The murine B7 (mB7) protein is a potent co-stimulatory molecule for the activation of murine CD4+ T cells. We have previously shown that stable mB7-transfected Chinese hamster ovary (CHO) cells synergize with either anti-CD3 monoclonal antibodies (mAb) or concanavalin A to stimulate T cell activation. In addition, mB7 can synergize with phorbol 12-myristate 13-acetate (PMA) to induce T cell activation in an alternative pathway. In the present report we describe the effects of three immunosuppressive drugs, cyclosporin A (CsA), FK 506, and mycalamide A on mB7-mediated T cell activation. The immunophilin ligands CsA and FK 506 block activation of murine CD4+ T cells by the combination of anti-CD3 mAb and CHO-mB7 cells but do not affect activation by CHO-mB7 cells and PMA. These results support the relevance of pharmacological studies of immunosuppressive compounds in the murine model prior to their application in man. In contrast to the effects of CsA and FK 506, mycalamide A blocks activation of murine CD4+ T cells by anti-CD3 mAb and mB7 as well as activation by mB7 and PMA. On a molar basis, mycalamide A appears to be at least 10-fold more potent than FK 506 which is 100-fold more potent than CsA. Because of its effects on multiple activation pathways and because of its potency, mycalamide A could have considerable therapeutic potential.
Animals↗
Renal dysplasia, megalocystis, and sirenomelia in four siblings.
First degree relatives of infants with bilateral renal agenesis or dysplasia have an increased risk of renal abnormalities including renal agenesis. We report a family in which four successive offspring exhibited a previously undescribed combination of congenital lethal renal disorders: bilateral renal dysplasia, megalocystis secondary to urethral obstruction and, sirenomelia with associated renal agenesis.
Abnormalities, Multiple↗
Murine B7 antigen provides a sufficient costimulatory signal for antigen-specific and MHC-restricted T cell activation.
We have previously shown that the murine B7 (mB7) molecule, when expressed in Chinese hamster ovary cells in stable fashion, can costimulate with anti-CD3 mAb or Con A to induce T cell activation. We have now derived, by gene transfection, Chinese hamster ovary cell lines that express the I-Ad molecule, either alone or in context with mB7. We have analyzed these transfectants for their capacity to present Ag to murine CD4+ T lymphocytes. I-Ad/mB7-double transfectants were able to stimulate mixed lymphocyte reactions and to present peptide Ag to specific T cells. Chinese hamster ovary cells that expressed only the I-Ad molecule were not able to stimulate T cell proliferation in these systems. Thus, the mB7 protein is a sufficient costimulatory molecule for the physiologic, Ag-dependent/MHC-restricted activation of murine CD4+ T cells. Stimulation of T cell bulk cultures resulted predominantly in the production of IL-2 and not of IL-4. The costimulatory activity of mB7 is not, however, restricted to the IL-2-secreting subset. We have identified one IL-4-secreting T cell clone, CDC35, which is responsive to mB7 triggering. Finally, we present experiments that suggest that mB7 and peptide/MHC complexes need to be expressed on the same cell for optimal induction of T cell activation.
Animals↗
Analysis of the association of peptides of optimal length to class I molecules on the surface of cells.
The association of major histocompatibility complex (MHC) class I molecules on the surface of cells with synthetic antigenic peptides of eight or nine amino acid residues was examined. Peptides were synthesized that correspond to the antigenic sequences from ovalbumin and influenza nucleoprotein believed to be naturally processed and presented by cells with Kb and Db MHC class I molecules, respectively. Consistent with the results of others, these peptides were 10(3)-10(5) times more active in stimulating specific T cells as compared to peptides of longer sequences. When cells are incubated with these peptides at less than 0.01-0.1 microM, the association of the peptides with class I molecules is dependent on (i) the reassociation of free beta 2-microglobulin from the extracellular fluids, (ii) a process that requires cells to be metabolically active, or (iii) stabilization of class I heterodimers by chemical crosslinking. In contrast, when cells are incubated with these peptides at greater than 0.1-1.0 microM, the peptides associate with class I molecules in the absence of exogenous beta 2-microglobulin, energy, or chemical crosslinking. Antigen competition experiments suggest that the class I molecules that bind peptides offered at high concentration become only transiently receptive to binding peptide. The concentration of peptides required for presentation to T cells under these conditions corresponds to those that stabilize Kb molecules on the surface of RMA-S mutant cells in the absence of exogenous beta 2-microglobulin. These results support the concept that the receptivity of class I molecules on cells is determined by the dissociation of beta 2-microglobulin from MHC class I that lacks bound peptides.
Animals↗
Heterogeneity in antigen processing by different types of antigen-presenting cells. Effect of cell culture on antigen processing ability.
The ability of normal B cells, peritoneal macrophages, and splenic APC to process and present OVA to a panel of T-T hybridomas with different specificities was investigated. In all cases, B cells were less efficient than unfractionated splenocytes in presenting OVA or its peptides. However, when the presentation of native Ag was compared to the presentation of peptides, it was obvious that there were marked differences in the ability of these two APC populations to generate different epitopes from OVA. Leupeptin inhibits the processing of selected epitopes from native OVA differently when it was presented by spleen cells or B cells, suggesting that these two APC populations differ in their protease content. The effect of in vitro culture on the ability of splenic and peritoneal APC to process OVA was also investigated. Native OVA presentation by macrophages and spleen cells was affected by in vitro culture, more for some epitopes than for other epitopes. In contrast, presentation of exogenous peptides by paraformaldehyde-fixed APC was either not affected by previous culturing for 3 days, or very much improved. Altogether, these data demonstrate that different epitopes on the same protein may be independently and differentially processed by B cells and spleen cells. Furthermore, the precise peptides that are produced may vary with the physiologic state of the APC.
Amino Acid Sequence↗
Serum proteases alter the antigenicity of peptides presented by class I major histocompatibility complex molecules.
Any effect of serum on the antigenicity of peptides is potentially relevant to their use as immunogens in vivo. Here we demonstrate that serum contains distinct proteases that can increase or decrease the antigenicity of peptides. By using a functional assay, we show that a serum component other than beta 2-microglobulin enhances the presentation of ovalbumin peptides produced by cyanogen bromide cleavage. Three features of this serum activity implicate proteolysis: it is temperature dependent, it results in increased antigenicity in a low molecular weight peptide fraction, and it is inhibited by the protease inhibitor leupeptin. Conversely, presentation of the synthetic peptide OVA-(257-264) is inhibited by serum. This inhibition is unaffected by leupeptin but is blocked by bestatin, a protease inhibitor with distinct substrate specificities. Implications for peptide-based vaccine design and immunotherapy are discussed.
Animals↗
Diversity in MHC class II ovalbumin T cell epitopes generated by distinct proteases.
It is generally accepted that a limited number of T cell epitopes are generated by APC from an immunogenic protein. To ascertain the number of determinants on OVA recognized in the context of the H-2s haplotype, we generated 19 T-T hybridomas against OVA and H-2s and we synthesized 46 overlapping peptides spanning the entire protein. Eighteen T-T hybrids were stimulated by eight different peptides. The peptide recognized by one T cell hybrid was not identified. The effect of four protease inhibitors on the processing and presentation of OVA by the LS.102.9 B cell hybridoma seemed to implicate several groups of proteases in the processing of this Ag. Alkylation of cysteine residues with iodoacetic acid showed in a few cases a dramatic decrease in the capacity of OVA to stimulate T-T hybrids recognizing cysteine-free peptides. In contrast, two T-T hybrids recognizing cysteine containing peptides were not affected by the alkylation, suggesting that alkylation inhibited the processing of OVA without affecting peptide interaction with class II MHC molecules. These data demonstrate that the repertoire of peptides generated by APC from OVA is not limited to one or few immunodominant peptides, and results from the activity of several endopeptidases and/or exopeptidases. In addition, the structure of the Ag (native or denatured) was shown to affect the efficiency with which different epitopes are generated.
Animals↗
Expression and function of the murine B7 antigen, the major costimulatory molecule expressed by peritoneal exudate cells.
The murine B7 (mB7) protein is a potent costimulatory molecule for the T-cell receptor (TCR)-mediated activation of murine CD4+ T cells. We have previously shown that stable mB7-transfected Chinese hamster ovary (CHO) cells but not vector-transfected controls synergize with either anti-CD3 monoclonal antibody-induced or concanavalin A-induced T-cell activation, resulting ultimately in lymphokine production and proliferation. We now have generated a hamster anti-mB7 monoclonal antibody. This reagent recognizes a protein with an apparent molecular mass of 50-60 kDa. The mB7 antigen is expressed on activated B cells and on peritoneal exudate cells (PECs). Antibody blocking experiments demonstrate that mB7 is the major costimulatory molecule expressed by PECs for the activation of murine CD4+ T cells. This suggests an important role for mB7 during immune-cell interactions. We have also surveyed a panel of murine cell lines capable of providing costimulatory activity. Our results indicate that mB7 is the major costimulatory molecule on some but not all cell lines and that there may be additional molecules besides mB7 that can costimulate the activation of murine CD4+ T cells.
Animals↗
Chemical cross-linking of class I molecules on cells creates receptive peptide binding sites.
Class I heterodimers on the surface of cells are generally unreceptive to binding peptides in the absence of exogenous beta 2-microglobulin. Paraformaldehyde covalently cross-links beta 2-microglobulin to class I heavy chains in situ and stabilizes empty class I heterodimers. Functionally, this cross-linking creates receptive class I peptide binding sites by acting on beta 2-microglobulin-associated molecules. The presentation of preexisting peptide-class I complexes is also enhanced. These findings support a model whereby a structural alteration, the dissociation of beta 2-microglobulin, limits the existence of receptive class I molecules on normal cells and may control the half-life of active class I molecules.
Animals↗
The class II MHC-restricted presentation of endogenously synthesized ovalbumin displays clonal variation, requires endosomal/lysosomal processing, and is up-regulated by heat shock.
LB27.4 cells (a B lymphoblastoid APC) were transfected with a plasmid containing an OVA cDNA. Functional analysis of six independent clones yielded three patterns of MHC-restricted presentation of the endogenously synthesized OVA. A clone displayed either: 1) strong class I and class II-restricted presentation, 2) strong class I but little or no class II-restricted presentation or, 3) only a modest class I-restricted presentation. There was no clonal variation in class II-restricted presentation of exogenous Ag or in the amount of surface class I or II molecules. Heat shock increased the presentation of endogenous but not exogenous Ag with class II. These results indicate that an endogenously synthesized Ag both constitutively and during heat shock can gain access to the class II, MHC-restricted, presentation pathway. The amount of OVA synthesized by a cell correlated with whether OVA-class II complexes were detected. However, the amount of OVA secreted into the extracellular fluid was not sufficient to sensitize APC, which suggests that endogenously synthesized OVA enters the class II pathway of Ag presentation by an intracellular route rather than by an extracellular/reuptake route. Also, the functional and quantitative analysis of the clones suggests that endogenously synthesized OVA was presented more efficiently with class I as compared to class II-MHC molecules. Leupeptin and chloroquine inhibited the class II-restricted presentation of endogenously synthesized OVA. Together these results indicate that endogenously synthesized OVA can gain access to an endosomal/lysosomal compartment via an intracellular route and be processed and presented in association with class II-MHC molecules.
Animals↗
Murine B7 antigen provides an efficient costimulatory signal for activation of murine T lymphocytes via the T-cell receptor/CD3 complex.
We demonstrate that the murine B7 (mB7) protein is a potent costimulatory molecule for the activation of resting murine CD4+ T cells through the T-cell receptor (TCR)/CD3 complex. Stable mB7-transfected Chinese hamster ovary cells, but not vector-transfected controls, synergize with anti-CD3 monoclonal antibody and Con A-induced T-cell activation, resulting ultimately in proliferation. mB7 exerted its effect by inducing production of interleukin 2 and expression of the interleukin 2 receptor. Thus, mB7 costimulates T-cell activation through the TCR/CD3 complex by positively modulating the normal pathway of T-cell expansion. In contrast to the pronounced effect of mB7 on the activation of T cells through the TCR/CD3 complex, the mB7-transfected CHO cell line costimulated T-cell activation via the glycosylphosphatidylinositol-anchored proteins Thy-1 and Ly-6A.2 only inefficiently. Finally, the combination of a calcium ionophore and mB7 is not sufficient to cause T-cell proliferation, while the combination of a calcium ionophore and phorbol 12-myristate 13-acetate (PMA) stimulates T cells efficiently. The signals that mB7 and PMA provide for murine T lymphocyte activation are therefore not interchangeable, although both costimulate activation through the TCR/CD3 complex.
Animals↗
The generation of immunogenic peptides can be selectively increased or decreased by proteolytic enzyme inhibitors.
The ability of splenic APC and a B cell hybridoma (LS.102.9) to process and present OVA to a panel of T-T hybridomas with different fine specificities was investigated. Splenic APC process and present OVA to all the T-T hybrids. The B cell hybridoma could similarly process and present OVA to some T-T hybrids but was very inefficient in stimulating two of the T cell hybridomas. The presentation of native OVA to these two T-T hybrids was significantly increased by leupeptin. Pulsing experiments demonstrated that leupeptin acted on the APC at a step before the processed Ag was displayed on the cell surface in association with MHC molecules. Leupeptin has no effect on the presentation of OVA peptides by LS.102.9 to the T-T hybrids. Leupeptin inhibits the generation of the epitopes of OVA that LS.102.9 produces under basal conditions. We also surveyed the effect of other protease inhibitors and observed similar augmenting and inhibitory effects on the presentation of selected OVA epitopes. The augmentation of processing by a protease inhibitor indicates that in the lysosomal/endosomal compartment proteases have capacity to both generate and destroy immunogenic peptides. Our data suggest that protease inhibitors could potentially be used as immunomodulators and are discussed in terms of physiology of the lysosomal/endosomal compartment.
Animals↗