Biomedical subjects

D A Mandelbrot

Publications and source records attributed to D A Mandelbrot.

12 recordsLinked to original sources

PubMed2001

Rejection of mouse cardiac allografts by costimulation in trans.

The activation of T cells by B7 costimulation in trans has been demonstrated in vitro, but the in vivo relevance is unknown. To study costimulation in trans of CD4(+) T cells in vivo, we performed cardiac transplants from B7-1/B7-2-deficient mice to recipients that do not express MHC class II molecules on peripheral APCs, but do have functional CD4(+) T cells (II(-)/4(+) mice). This model restricts the B7-dependent activation of CD4(+) T cells to costimulation in trans and excludes any contribution from indirect Ag presentation. We find that II(-)/4(+) recipients reject B7-deficient grafts as rapidly as wild-type grafts, suggesting that costimulation in trans can mediate rejection as potently as costimulation in cis. Treatment of II(-)/4(+) recipients of B7-deficient grafts with depleting Abs to CD4 or CD8 demonstrates that indirect Ag presentation to CD8(+) cells does not significantly contribute to rejection. This is the first demonstration that costimulation in trans can mediate an immune response in vivo and has important therapeutic implications.

Animals↗

PubMed2001

CD28-independent costimulation of T cells in alloimmune responses.

T cell costimulation by B7 molecules plays an important role in the regulation of alloimmune responses. Although both B7-1 and B7-2 bind CD28 and CTLA-4 on T cells, the role of B7-1 and B7-2 signaling through CTLA-4 in regulating alloimmune responses is incompletely understood. To address this question, we transplanted CD28-deficient mice with fully allogeneic vascularized cardiac allografts and studied the effect of selective blockade of B7-1 or B7-2. These mice reject their grafts by a mechanism that involves both CD4(+) and CD8(+) T cells. Blockade of CTLA-4 or B7-1 significantly accelerated graft rejection. In contrast, B7-2 blockade significantly prolonged allograft survival and, unexpectedly, reversed the acceleration of graft rejection caused by CTLA-4 blockade. Furthermore, B7-2 blockade prolonged graft survival in recipients that were both CD28 and CTLA-4 deficient. Our data indicate that B7-1 is the dominant ligand for CTLA-4-mediated down-regulation of alloimmune responses in vivo and suggest that B7-2 has an additional receptor other than CD28 and CTLA-4 to provide a positive costimulatory signal for T cells.

Abatacept↗

PubMed2001

B7-dependent T-cell costimulation in mice lacking CD28 and CTLA4.

To examine whether B7 costimulation can be mediated by a molecule on T cells that is neither CD28 nor CTLA4, we generated mice lacking both of these receptors. CD28/CTLA4(-/-) mice resemble CD28(-/-) mice in having decreased expression of T-cell activation markers in vivo and decreased T-cell proliferation in vitro, as compared with wild-type mice. Using multiple approaches, we find B7-dependent costimulation in CD28/CTLA4(-/-) mice. The proliferation of CD28/CTLA4(-/-) T cells is inhibited by CTLA4-Ig and by the use of antigen-presenting cells lacking both B7-1 and B7-2. CD28/CTLA4(-/-) T-cell proliferation is increased by exposure to Chinese hamster ovary cells transfected with B7-1 or B7-2. Finally, administration of CTLA4-Ig to CD28/CTLA4(-/-) cardiac allograft recipients significantly prolongs graft survival. These data support the existence of an additional receptor for B7 molecules that is neither CD28 nor CTLA4.

Abatacept↗

PubMed2000

Molecular basis for leukocyte integrin alpha(E)beta(7) adhesion to epithelial (E)-cadherin.

Cadherins are expressed in tissue-restricted patterns and typically mediate homophilic adhesion. Cadherins also mediate lymphocyte adhesion, providing the opportunity for lymphocyte attachment to parenchymal cells. The best characterized example of lymphocyte adhesion to a tissue-specific cell adhesion molecule, as opposed to a vascular endothelial adhesion molecule, is the interaction between integrin alpha(E)beta(7) on intraepithelial lymphocytes and E-cadherin on epithelial cells. However, the molecular basis for an integrin-cadherin interaction is not well defined. Realization that the cadherin domain adopts a topology similar to the immunoglobulin (Ig) fold suggested that integrin recognition of E-cadherin might be similar to recognition of Ig superfamily ligands. Thus, we modeled domain 1 of human E-cadherin and studied the role of solvent-exposed loops that connect Ig-like core-forming beta strands. Mutational analyses localized the integrin alpha(E)beta(7) recognition site to the top of domain 1 at the face formed by the BC and FG loops, a site distinct from the region recognized in intercellular adhesion molecule (ICAM)-1, -2, and -3, mucosal addressin cell adhesion molecule 1 (MAdCAM-1), vascular cell adhesion molecule 1 (VCAM-1), and fibronectin by their integrin ligands. Moreover, the integrin alpha(E)beta(7) binding site is distinct from the homophilic binding site on E-cadherin. These studies provide a conceptual basis for integrin-cadherin binding and extend the model that an Ig-like fold can serve as a scaffold for recognition.

Amino Acid Sequence↗

PubMed2000

Association of B7-1 co-stimulation with the development of graft arterial disease. Studies using mice lacking B7-1, B7-2, or B7-1/B7-2.

To investigate the roles of B7-1 and/or B7-2 co-stimulatory molecule in the development of graft arterial disease (GAD), major histocompatibility complex (MHC) class II-mismatched allograft hearts were transplanted into wild-type, B7-1(-/-), B7-2(-/-), or B7-1/B7-2(-/-) recipient mice. Grafts were explanted at 4 or 8 weeks and used for histological and immunohistochemical analyses, RNase protection assay, and flow cytometry of graft infiltrating cells. Grafts in wild-type recipients showed macrophage, recipient MHC class II, and B7 molecule co-localization by immunohistochemistry to GAD lesions. Flow cytometry revealed that CD11b(+) and MHC class II(+) graft infiltrating cells expressed B7-1 more than B7-2, whereas B7-2 expression was predominant in CD11b(-) cells at 4 and 8 weeks. GAD was significantly attenuated in the allografts in B7-1(-/-) and B7-1/B7-2(-/-) but not in B7-2(-/-) recipients compared to wild-type hosts. Interferon-gamma mRNA levels were comparable in all graft combinations, whereas interleukin-4 mRNA levels decreased in grafts in B7-2 deficient hosts, but did not correlate with GAD attenuation. The findings indicate distinct roles for B7-1 and B7-2 co-stimulatory molecules in the development of GAD, potentially because of differential expression of B7-1 and B7-2 molecules on distinct stimulator and/or effector cell populations.

Animals↗

PubMed1999

Expression of B7 molecules in recipient, not donor, mice determines the survival of cardiac allografts.

Blockade of the CD28/CTLA4/B7 costimulatory pathway using CTLA4-Ig has great therapeutic potential, and has been shown to prolong allograft survival in a variety of animal models. To gain further insight into the mechanism by which costimulatory blockade prevents allograft rejection, we studied cardiac allograft survival in the complete absence of B7 costimulation using mice lacking B7-1 and B7-2 (B7-1/B7-2-/- mice). To determine the role of B7 on donor vs recipient cells, we used B7-1/B7-2-/- mice as either donors or recipients of allografts. Wild-type (WT) recipients acutely reject fully allogeneic hearts from both WT and B7-1/B7-2-/- mice. In contrast, B7-1/B7-2-/- recipients allow long-term survival of grafts from both WT and B7-1/B7-2-/- mice, with minimal histologic evidence of either acute or chronic rejection in grafts harvested after 90 days. The B7-1/B7-2-/- mice acutely reject B7-1/B7-2-/- allografts if CD28 stimulation is restored by the administration of Ab to CD28 and can mount an alloresponse in mixed lymphocyte reactions. Therefore, B7-1/B7-2-/- mice are capable of generating alloresponses both in vivo and in vitro. Our results demonstrate that in the alloresponse to mouse heterotopic cardiac transplantation, B7 molecules on recipient cells rather than donor cells provide the critical costimulatory signals. The indefinite survival of allografts into B7-1/B7-2-/- recipients further shows that the absence of B7 costimulation alone is sufficient to prevent rejection.

Abatacept↗

PubMed1999

The role of CTLA-4 in regulating Th2 differentiation.

To examine the role of CTLA-4 in Th cell differentiation, we used two newly generated CTLA-4-deficient (CTLA-4-/-) mouse strains: DO11. 10 CTLA-4-/- mice carrying a class II restricted transgenic TCR specific for OVA, and mice lacking CTLA-4, B7.1 and B7.2 (CTLA-4-/- B7.1/B7.2-/- ). When purified naive CD4+ DO11.10 T cells from CTLA-4-/- and wild-type mice were primed and restimulated in vitro with peptide Ag, CTLA-4-/- DO11.10 T cells developed into Th2 cells, whereas wild-type DO11.10 T cells developed into Th1 cells. Similarly, when CTLA-4-/- CD4+ T cells from mice lacking CTLA-4, B7. 1, and B7.2 were stimulated in vitro with anti-CD3 Ab and wild-type APC, these CTLA-4-/- CD4+ T cells produced IL-4 even during the primary stimulation, whereas CD4+ cells from B7.1/B7.2-/- mice did not produce IL-4. Upon secondary stimulation, CD4+ T cells from CTLA-4-/- B7.1/B7.2-/- mice secreted high levels of IL-4, whereas CD4+ T cells from B7.1/B7.2-/- mice produced IFN-gamma. In contrast to the effects on CD4+ Th differentiation, the absence of CTLA-4 resulted in only a modest effect on T cell proliferation, and increased proliferation of CTLA-4-/- CD4+ T cells was seen only during secondary stimulation in vitro. Administration of a stimulatory anti-CD28 Ab in vivo induced IL-4 production in CTLA-4-/- B7.1/B7.2-/- but not wild-type mice. These studies demonstrate that CTLA-4 is a critical and potent inhibitor of Th2 differentiation. Thus, the B7-CD28/CTLA-4 pathway plays a critical role in regulating Th2 differentiation in two ways: CD28 promotes Th2 differentiation while CTLA-4 limits Th2 differentiation.

Abatacept↗

PubMed1999

B7-1 or B7-2 is required to produce the lymphoproliferative phenotype in mice lacking cytotoxic T lymphocyte-associated antigen 4 (CTLA-4).

The costimulatory molecules B7-1 and B7-2 regulate T lymphocyte activation by delivering activating signals through CD28 and inhibitory signals through cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). The importance of CTLA-4-mediated inhibition was demonstrated by the uncontrolled T cell activation and lymphoproliferative disease that develops in CTLA-4-deficient (-/-) mice. To examine the role of B7 signaling in the activation of CTLA-4-deficient T cells, we bred CTLA-4(-/-) mice with mice lacking B7-1, B7-2, or both B7 molecules. The CTLA-4/B7-1(-/-) and the CTLA-4/B7-2(-/-) mice develop lymphoproliferation and enhanced T cell activation. Mice lacking CTLA-4, B7-1, and B7-2 have a normal life-span, and do not have lymphocytic infiltrates in any organs, or increased T cell activation. Therefore, the two B7 molecules have overlapping functions, since either B7-1 or B7-2 alone can cause the CTLA-4(-/-) phenotype. Elimination of both B7-1 and B7-2 from the CTLA-4- deficient mouse abrogates the lymphocyte activation and disease, and does not reveal evidence for additional stimulatory CD28 ligands. The CTLA-4(-/-) phenotype can be reproduced with anti-CD28 antibody in mice lacking CTLA-4, B7-1, and B7-2, but wild-type mice are unaffected by the same treatment. This suggests that the inhibitory function of CTLA-4 can overcome strong CD28-mediated signaling in vivo.

Abatacept↗

PubMed1999

CTLA-4 and T cell activation.

The past year has seen significant advances in our understanding of the role of cytotoxic T lymphocyte antigen 4 (CTLA-4) in regulating T cell activation and tolerance. Recent studies indicate that CTLA-4 not only counterbalances CD28 signals but also can inhibit T cell responses independently of CD28. Recent work has also revealed a role for CTLA-4 in regulating Th1/Th2 differentiation. Manipulation of CTLA-4 in animal models of autoimmunity has shown that CTLA-4 regulates both the initiation and the progression of autoimmune diseases.

Abatacept↗

PubMed1994

Distinct structural and functional epitopes of the alpha E beta 7 integrin.

Intestinal intraepithelial lymphocytes (iIEL) are predominantly CD3+, CD8+ T lymphocytes located above or adjacent to the mucosal basement membrane. Although they are positioned to interact with intercellular luminal antigen or with enterocytes, the function of iIEL remains unknown. Most (> 85%) of the iIEL express the alpha E beta 7 integrin which appears to be involved in the adhesion of lymphocytes to epithelial cells. We report the characterization of three monoclonal antibodies (mAb) termed alpha E7-1, alpha E7-2, and alpha E7-3, that react with the alpha E beta 7 integrin recognized by the previously described mAb HML-1 as demonstrated by identical sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobility and charge. Flow cytometric analysis of antibody cross-blocking indicated that these mAb recognize distinct epitopes of alpha E beta 7. While all of the mAb were capable of blocking the adhesion of cultured iIEL to a breast epithelial cell line, only HML-1 and alpha E7-1 (which recognize an identical or closely related epitope) were co-stimulatory with suboptimal concentrations of anti-CD3 mAb in inducing proliferation of cultured iIEL. Thus, these mAb appear to recognize functionally distinct epitopes of alpha E beta 7 and will be useful to study relationships between the structure and function of this integrin.

Animals↗

PubMed1990

A survey of exposures, practices and recommendations of surgeons in the care of patients with human immunodeficiency virus.

Policy makers face a conflict between satisfying concerns of health care workers (HCW) about the occupational risk of human immunodeficiency virus (HIV) infection and ensuring adequate care for patients. This conflict is particularly severe in the field of surgery. We mailed a questionnaire on the surgical care of patients infected with HIV to 1,461 surgeons in New York City and Philadelphia, and 551 (37.7 per cent) responded. Although 1.9 per cent currently were testing all patients for HIV, 42.6 per cent of surgeons believed that all patients in their hospital should be tested. Of the surgeons who responded, 6.3 per cent refused to treat any patient infected with HIV. Less than 50 per cent recommended the use of barrier precautions on all patients in their hospital. Surgeons in New York City were significantly more likely than those in Philadelphia to favor separate facilities for HIV-infected patients. Surgeons considering themselves at higher occupational risk were more likely than those at lower risk to favor widespread testing, separate facilities and use of precautions. Surgeons reported a wide range of opinions. Their approach to the use of barrier precautions differs from the Centers for Disease Control recommendations. The patterns observed suggest that distinct policies may be appropriate for different hospitals.

Female↗

PubMed1987

Identification and characterization of a polypeptide from a lobster neurosecretory gland that induces cyclic GMP accumulation in lobster neuromuscular preparations.

Several observations suggest that cyclic GMP might regulate some aspect of neuromuscular physiology or metabolism in the lobster. Homarus americanus: lobster muscle is one of the richest known sources of cyclic GMP-dependent protein kinase, the preparation contains several phosphoproteins whose state of phosphorylation is affected by cyclic GMP more effectively than by cyclic AMP, and guanylate cyclase and phosphodiesterase are active in this tissue. However, no factor has yet been identified that alters lobster muscle cyclic GMP levels. We have screened extracts of neural and neurosecretory structures for the capacity to promote cyclic GMP accumulation in isolated exoskeletal muscles. Extracts of the sinus gland (a neurohemal organ found in the eyestalk) contain a factor that induces up to 100-fold increases in muscle cyclic GMP content, whereas extracts of other tissues are ineffective. This factor can also act on targets other than muscle, with hepatopancreas, testis, and neuronal tissue showing the largest responses. The sinus gland factor does not appear to affect cyclic GMP metabolism by depolarizing the preparation or by mobilizing extracellular Ca2+. The effect on cyclic GMP levels is dose-dependent and linear with time. Biological activity is destroyed by boiling and by 90% ethanol. It is also destroyed by trypsin, chymotrypsin, or pronase, which suggests that the factor is a protein or peptide. Both gel filtration chromatography and experiments using dialysis tubing with different molecular weight exclusion limits indicate that the factor has an apparent molecular weight of 5,000-12,000 daltons. A preliminary fractionation scheme, based on gel filtration, ion-exchange, and reverse-phase chromatography, gives greater than 1,300-fold purification. Our long-range goal is to purify this factor to homogeneity, compare it to other peptide hormones, and use it as a probe to evaluate the role of cyclic GMP at the neuromuscular junction.

Animals↗