Multi-modality parathyroid imaging: A shifting paradigm.

The goal of parathyroid imaging in hyperparathyroidism is not diagnosis, rather it is the localization of the cause of hyperparathyroidism for planning the best therapeutic approach. Hence, the role of imaging to accurately and precisely localize the abnormal parathyroid tissue is more important than ever to facilitate minimally invasive parathyroidectomy over bilateral neck exploration. The common causes include solitary parathyroid adenoma, multiple parathyroid adenomas, parathyroid hyperplasia and parathyroid carcinoma. It is highly imperative for the radiologist to be cautious of the mimics of parathyroid lesions like thyroid nodules and lymph nodes and be able to differentiate them on imaging. The various imaging modalities available include high resolution ultrasound of the neck, nuclear imaging studies, four-dimensional computed tomography (4D CT) and magnetic resonance imaging. Contrast enhanced ultrasound is a novel technique which has been recently added to the armamentarium to differentiate between parathyroid adenomas and its mimics. Through this review article we wish to review the imaging features of parathyroid lesions on various imaging modalities and present an algorithm to guide their radiological differentiation from mimics.

Insulinoma Presenting with Neuropsychiatric Symptoms.

An insulinoma is a rare pancreatic endocrine tumor which is typically a hypervascular, solitary small tumour. 90 % of tumors are benign and less than 2 cm in size. Some insulinomas are associated with MEN-1 syndrome. Some cases of insulinoma may present with neuropsychiatric symptoms and may be wrongly diagnosed as psychosis. We report a case of insulinoma in a 55 years old female who presented with episodes of abnormal behavior and altered sensorium. On detailed investigations she was diagnosed as a case of hyperinsulinemic hypoglycemia due to insulinoma (in her case MRI abdomen was normal) DOTANOC PET CT confirmed the insulinoma in body/tail of pancreas.

The oncofetal protein, 5T4, is a suitable target for antibody-guided anti-cancer chemotherapy with calicheamicin.

The oncofetal protein, 5T4, is a tumor-associated protein displayed on the cell membrane of various carcinomas. This molecule is a promising target for anti-tumor vaccine development and for targeted therapy with staphylococcus exotoxin. The potential use of 5T4 as a target for antibody-guided chemotherapy has not been demonstrated. We report oncolytic efficacy and selectivity in vitro and in vivo with immuno-conjugates of calicheamicin (CM) and the anti-5T4 antibody, H8. CM is a potent cytotoxic drug that causes double strand breaks in DNA. Conjugates of CM and H8 were constructed with acid-labile as well as acid-stabile linkers. In vitro, when applied to monolayers of 5T4(+) cells, CM-conjugates targeting 5T4 were consistently more toxic than either free drug or a non-binding control CM-conjugate. This difference was less pronounced on 5T4-deficient cells. In vivo, four 5T4-positive subcutaneous tumor models were treated with conjugates. Efficacy was demonstrated by reduction of tumor growth relative to controls treated with drug vehicle. To evidence selectivity, the efficacy of the anti-5T4 conjugates was compared to the efficacy of H8, a mixture of H8 and calicheamicin, calicheamicin alone or calicheamicin conjugated to the anti-CD33 antibody, hP67.6. In addition, the efficacy and selectivity of an acid-labile conjugate of H8 was evaluated in an orthotopic model for 5T4(+) lung cancer. Increased survival following treatment was used as a parameter of efficacy. Calicheamicin conjugates of H8 were effective and selective in all the examined tumor models. Differences in efficacy between the acid-labile and acid-stabile conjugates depended on the investigated tumor model.

Therapeutic potential of CD22-specific antibody-targeted chemotherapy using inotuzumab ozogamicin (CMC-544) for the treatment of acute lymphoblastic leukemia.

CMC-544 (inotuzumab ozogamicin) is a CD22-specific cytotoxic immunoconjugate of calicheamicin intended for the treatment of B-lymphoid malignancies. This preclinical study investigated antitumor activity of CMC-544 against CD22+ acute lymphoblastic leukemia (ALL). CMC-544 inhibited in vitro growth of ALL cell lines more potently than that of Ramos B-lymphoma cells. When administered to nude mice with established sc xenografts of REH ALL, CMC-544 caused dose-dependent inhibition of xenograft growth producing complete tumor regression and cures in tumor-bearing mice at the highest dose of 160 microg/kg of conjugated calicheamicin. In contrast, a nonbinding control conjugate was 16-fold less effective than CMC-544 in inhibiting growth of REH ALL xenografts. When REH cells were injected intravenously in scid mice and allowed to disseminate systemically, mice developed hind-limb paralysis that was effectively prevented by treatment with CMC-544. Flow cytometric analysis of cells recovered from the bone marrow from mice with disseminated disease verified the presence of engrafted ALL cells. Significantly reduced numbers of ALL cells were recovered from the bone marrow of CMC-544-treated mice than from vehicle-treated mice with disseminated disease. The anti-leukemia activity of CMC-544 demonstrated here further supports clinical evaluation of CMC-544 for the treatment of CD22+ leukemia.

Cellular and humoral immune responses to Borrelia burgdorferi antigens in patients with culture-positive early Lyme disease.

We determined cellular and humoral immune responses to Borrelia burgdorferi lysate and to recombinant flagellin (FlaB), OspC, and OspA in acute- and convalescent-phase samples from 39 culture-positive patients with erythema migrans and in 20 healthy control subjects. During the acute illness, a median of 4 days after the onset of erythema migrans, 51% of the patients had proliferative cellular responses and 72% had antibody responses to at least one of the borrelial antigens tested. During convalescence, at the conclusion of antibiotic therapy, 64% of the patients had proliferative cellular reactivity and 95% had antibody reactivity with at least one of the spirochetal antigens tested. In both acute- and convalescent-phase samples, cellular immune responses were found as frequently to OspA as to OspC and FlaB. Although antibody responses were also frequently seen to OspC and FlaB, only a few patients had marginal antibody reactivity with OspA. The percentage of patients with proliferative responses was similar in those with clinical evidence of localized or disseminated infection, whereas humoral reactivity was found more often in those with disseminated disease. We conclude that cellular and humoral responses to B. burgdorferi antigens are often found among patients with early Lyme disease. In contrast with the other antigens tested, cellular but not humoral reactivity was often found with OspA.

Costimulation of T lymphocytes with integrin ligands intercellular adhesion molecule-1 or vascular cell adhesion molecule-1 induces functional expression of CTLA-4, a second receptor for B7.

Costimulation by the CD28 ligand B7/BB1 plays an important role during T cell proliferation primarily by augmenting synthesis of IL-2 and other cytokines. Resting CD4+ T cells express CD28 but not CTLA-4 on their surface. Costimulation of T cells with ICAM-1 or VCAM-1 induced CTLA-4 expression and up-regulated CD28 expression. CD28 and CTLA-4 were independently distributed on the surface of activated T lymphoblasts. When co-immobilized with anti-TCR mAb both anti-CD28 and anti-CTLA-4 mAb augmented T cell proliferation. Although anti-CD28-mediated augmentation of T cell proliferation was stronger than that seen with anti-CTLA-4 mAb, together these two mAb caused supraadditive augmentation of T cell proliferation. The augmentation of the effects of anti-CD28 mAb by anti-CTLA-4 mAb was greater at low occupancy of CD28 by anti-CD28 mAb. Costimulation of CD28+ CTLA-4+ T cells with anti-CTLA-4 caused three- to fivefold increase in IL-2 production, whereas similar treatment with anti-CD28 caused > 40-fold increase. The costimulatory effect of B7 on primed T cells was partially inhibited by Fab anti-CD28 mAb. Anti-CTLA-4 mAb alone did not inhibit B7-induced response but caused modest increase in the inhibitory effect of anti-CD28 Fab. On integrin-mediated costimulation, Ag-specific CD4+ T cell lines also up-regulated their CTLA-4 expression, and proliferation of these cells was augmented by anti-CTLA-4 mAb. Unlike that of CD28, ligation of CTLA-4 alone failed to mobilize intracellular [Ca2+]. However, coligation of CTLA-4 and TCR induced stronger [Ca2+] response in Ag-specific T cell lines than that seen with TCR alone. These results suggest that integrin-costimulated T cells express CTLA-4 and can be costimulated via CTLA-4. Optimal development of various immune functions may involve combined costimulation via both CD28 and CTLA-4.

Costimulation of T-cell activation and virus production by B7 antigen on activated CD4+ T cells from human immunodeficiency virus type 1-infected donors.

Infection with the human immunodeficiency virus type 1 (HIV-1) requires T-cell activation. Recent studies have shown that interactions of the T-lymphocyte receptors CD28 and CTLA-4 with their counter receptor, B7, on antigen-presenting cells are required for optimal T-cell activation. Here we show that HIV-1 infection is associated with decreased expression of CD28 and increased expression of B7 on CD4+ T-cell lines generated from seropositive donors by alloantigen stimulation. Loss of CD28 expression was not seen on CD4+ T-cell lines from seronegative donors, but up-regulation of B7 expression was observed upon more prolonged culture. Both T-cell proliferation and interleukin 2 mRNA accumulation in HIV-1-infected cultures required costimulation with exogenous B7 because these events were blocked by CTLA4Ig, a soluble form of CTLA-4 that binds B7 with high avidity. In contrast, levels of HIV-1 RNA were not affected by CTLA4Ig, indicating that regulation of virus transcription in these cultures did not depend upon CD28-B7 engagement. Infected T cells could present alloantigen to fresh, uninfected CD4+ T cells, leading to increased proliferation and virus spread to the activated cells. Both of these events were blocked by CTLA4Ig. Thus, chronic activation of HIV-1-infected CD4+ T cells reduces expression of CD28 and increases expression of B7, thereby enabling these T cells to become antigen-presenting cells for uninfected CD4+ T cells; this might be another mechanism for HIV-1 transmission via T-cell-T-cell contact.

Costimulation with integrin ligands intercellular adhesion molecule-1 or vascular cell adhesion molecule-1 augments activation-induced death of antigen-specific CD4+ T lymphocytes.

Integrin ligands intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) can efficiently costimulate proliferation of resting T cells but not that of Ag-specific T cells. In contrast, CD28 ligand B7 and CD2 ligand leukocyte function-associated Ag (LFA-3) can support IL-2 synthesis and proliferation of Ag-specific T cells more efficiently than that of resting T cells. The molecular basis for this differential costimulation of T cells is poorly understood. In this study, using mAb and soluble IgC gamma 1 chimeras of these adhesion molecules, we demonstrate that coligation of the TCR and CD11a/CD18 (LFA-1/beta 2 integrin) or CD29/CD49d (very late activation Ag-4/beta 1 integrin) using anti-TCR mAb and either ICAM-1 or VCAM-1 induces activation-dependent death of DRw6-specific CD4+ T cells. Similar coligation of the TCR with CD2 or CD28 using either mAb or ligands LFA-3 or B7 not only lacked the ability to induce death but also failed to reverse or inhibit integrin-facilitated death of DRw6-specific T cells. Each of these ligands augmented anti-TCR mAb-induced transcription of IL-2 and IL-4 genes. Exogenous addition of IL-2 and IL-4 did not reverse the integrin-supported T cell death. The death-promoting costimulatory effects of ICAM-1 and VCAM-1 were observed with Ag-specific chronically stimulated T cells but not with either resting T cells or those activated in short-term cultures. Treatment of T cells with cyclosporin A or a protein tyrosine kinase inhibitor herbimycin A inhibited ICAM-1 or VCAM-1-promoted activation-induced T cell death. The Ag-specific T cells that survived death-promoting effects of ICAM-1 or VCAM-1 proliferated efficiently upon restimulation with these ligands. Exposure of DRw6-specific T cells to DRw6+ B7+ ICAM-1+ LFA-3+ VCAM-1+ APC but not DR3+ B7+ ICAM-1+ LFA-3+ VCAM-1+ APC induced death of these T cells. This effect was blocked by pretreatment of T cells with mAb directed at CD18 or CD29 but not with those against CD2 or CD28. Taken together, these results suggest that TCR-directed engagement of integrins by their ligands ICAM-1 or VCAM-1 induces activation-dependent death of some perhaps more differentiated Ag-specific T cells and this may be an important homeostatic mechanism by which functional expression of Ag-specific T cells is regulated during an ongoing immune response.

Beta 2-integrin LFA-1 signaling through phospholipase C-gamma 1 activation.

One of the beta 2-integrins found on hematopoietic cells is lymphocyte function-associated antigen 1 (LFA-1), a lymphocyte/myeloid cell-specific receptor that binds to members of the intercellular adhesion molecule (ICAM) family on antigen-presenting cells. Stimulation of LFA-1 with antibodies or purified ICAMs induces augmentation of T-cell antigen receptor (TCR)-directed T-cell responsiveness. In the present study, LFA-1 was shown to be linked to the tyrosine kinase signaling pathway that stimulates tyrosine phosphorylation and activation of phospholipase C-gamma 1 (PLC-gamma 1). Integrin beta-chain (CD18) crosslinking independently induced downstream mobilization of intracellular Ca2+ and potently costimulated TCR-induced Ca2+ flux with an increase in both amplitude and kinetics. beta 2-Integrin signaling through this pathway was completely inhibited by herbimycin A and was prevented by TCR modulation. Coligation of the TCR via antibody and LFA-1 with a counter-receptor in the form of a soluble ICAM-1/Rg fusion protein resulted in prolonged tyrosine phosphorylation of PLC-gamma 1. Monoclonal antibodies to both the alpha chain (CD11a) and the beta chain (CD18) of LFA-1 induced Ca2+ mobilization to different levels, suggesting epitope specificity for activation potential. In addition to PLC-gamma 1, tyrosine phosphorylation of an 80-kDa protein substrate was augmented following CD18 crosslinking but was not TCR-dependent. The beta 2-integrin LFA-1 on T cells is therefore directly linked to a tyrosine kinase pathway that stimulates signaling by phosphatidylinositol-specific PLC-gamma 1.

Activation with superantigens induces programmed death in antigen-primed CD4+ class II+ major histocompatibility complex T lymphocytes via a CD11a/CD18-dependent mechanism.

Staphylococcal enterotoxin superantigens (SAg) bind class II major histocompatibility complex (MHC) molecules on antigen-presenting cells (APC) and upon cell-to-cell contact stimulate proliferation of T cells expressing appropriate V beta gene products. In addition, SAg can also deliver negative signals to Ag-specific T cells resulting in a state of unresponsiveness or a loss of viability. The present study examines the functional consequences of a direct interaction of SAg with alloAg-specific class II MHC+ CD4+ T cell lines (TCL). Our results demonstrate that SAg induce programmed death (apoptosis) in a majority of Ag-specific CD4+ T cells accompanied by genomic DNA fragmentation. SAg binding to Ag-specific TCL resulted in a rapid mobilization of intracellular free calcium ([Ca2+]i) and transcription of a number of cytokine genes including interleukin-2(IL-2), IL-4, interferon-gamma (IFN-gamma), granulocyte-macrophage colony-stimulating factor (GM-CSF), and granzyme B indicating the activation of primed T cells. Both SAg-induced cytokine gene expression as well as subsequent death were significantly inhibited by a tyrosine kinase inhibitor herbimycin A and also by cyclosporin A. SAg-induced death of primed T cells was also inhibited by monoclonal antibodies (mAb) directed at the CD11a/CD18 molecule but not those reactive with other T cell surface molecules such as CD2, CD7, CD28, CD29 or CD49d. None of these mAb, including anti-CD11a/CD18, had any effect on SAg-induced expression of IL-2 and IL-4 genes or SAg-induced [Ca2+]i response. Addition of cytokines such as IL-1 alpha, IL-2, IL-4, IL-6, GM-CSF, IFN-gamma, tumor necrosis factor (TNF-alpha, or TNF-beta), or neutralizing Ab to these cytokines had no effect on SAg-induced death of Ag-specific TCL. The T cells which survived the death-inducing effects of SAg showed down-regulation of the CD3/T cell receptor and up-regulation of CD2 and HLA-DR expression, and upon re-exposure to the same SAg upregulated expression of mRNA for IL-2 and IFN-gamma. Presentation of SAg by B7+ ICAM-1+ LFA-3+ DR+ professional APC was also able to induce the death of Ag-specific TCL. Together these results suggest that the activation with SAg causes programmed death of Ag-specific TCL cells via a mechanism that requires late participation of the CD11a/CD18 molecule.

Bispecific receptor globulins, novel tools for the study of cellular interactions. Preparation and characterization of an E-selectin/P-selectin bispecific receptor globulin.

In recent years the functional consequences of receptor/ligand interactions have been studied in vitro and in vivo using monospecific recombinant immunoglobulin fusion proteins (recombinant/receptor globulins, Rg). These proteins are encoded by chimeric genes composed of a DNA fragment encoding the extracellular domain of a cell surface protein grafted onto a DNA fragment encoding immunoglobulin constant domains. In order to extend the range of applications of Rgs we investigated the possibility of preparing bispecific Rgs. These bispecific fusion proteins contain the extracellular domains of two cell surface proteins held together in close proximity by the constant domains of an immunoglobulin. Here we describe the preparation and characterization of a bispecific Rg which contains the extracellular domains of two adhesion molecules expressed by activated vascular endothelial cells, E-selectin and P-selectin. These two proteins play an important role in initiating leukocyte adhesion to the vascular cell wall at sites of inflammation. Binding studies showed that the E-selectin/P-selectin bispecific immunoglobulin fusion protein (ELAM-1/GMP140 Rg) has an enhanced ability to bind to the myeloid cell line HL60 when compared to the monospecific Rg fusion proteins from which it was derived.

Regulation of HIV production by blood mononuclear cells from HIV-infected donors: II. HIV-1 production depends on T cell-monocyte interaction.

Cell-cell interactions induced between T cells and monocytes by certain soluble anti-CD3 monoclonal antibodies (MAbs) were previously shown to be required for high-level production of HIV-1 by peripheral blood mononuclear cells (PBMCs) from infected donors. Staphylococcal enterotoxin or superantigen (SAg) is another mitogen inducing monocytes-T cell interactions that exhibit potent induction of HIV-1 production. Antibodies to several adhesion molecules were used to test the requirements for T cell- and monocyte-associated adhesion molecules in HIV-1 production following activation with anti-CD3 or SAg. Blocking of either CD2-LFA-3, or CD18-ICAM-1, inhibited anti-CD3- or SAg-induced HIV-1 production by more than 90% without inhibiting CD4+ T cell proliferation. Inhibition of HIV production was observed when either the T cell or monocyte coreceptor was bound by MAbs to these adhesion molecules. Blocking of CD28-B7 interactions by soluble CTLA-4 fusion protein, a CD28 homolog, inhibited both HIV-1 production and CD4+ T cell proliferation. Fc binding was not required for HIV-1 inhibition by MAbs to CD2 and CD18, because Fab or F(ab')2 fragments of these MAbs inhibited HIV-1 production by more than 80%. A chimeric single-chain MAb to CD2 was produced, containing heavy and light chain variable regions from MAb 35.1 to CD2 linked to the constant regions of human IgG1 (CD2 SFv-Ig). This humanized CD2 SFv-Ig inhibited HIV-1 production by 30% to > 98%. These results thus indicate that simultaneous engagement of multiple adhesion pathways between T cells and monocytes are required for HIV production by patients PBMCs and may have implications for therapy of HIV infections.

Costimulation via vascular cell adhesion molecule-1 induces in T cells increased responsiveness to the CD28 counter-receptor B7.

Optimal stimulation of CD4+ T cells in an immune response requires not only signals transduced via the CD3/TCR complex but also costimulatory signals delivered as a consequence of interactions between T-cell surface-associated costimulatory R and their counter-R on APC. CD28 plays a crucial role as a dominant costimulatory R during the induction of CD4+ T-cell proliferation by interacting with counter-R B7 on APC to sustain IL-2 production. The absence of CD28-mediated costimulation has been postulated to result in T-cell anergy or unresponsiveness. The costimulatory effects of CD28 can be generated with its natural counter-R B7 or mAb directed at CD28. Using soluble C gamma 1 chimeras of B7, ICAM-1, and VCAM-1, we have recently shown that B7 costimulates TCR-dependent proliferation of Ag-primed CD4+ T cells more efficiently than that of resting nonactivated CD4+ T cells. In contrast, proliferation of resting CD4+ T cells can be efficiently costimulated by either ICAM-1 or VCAM-1 via interactions with their R CD11a/CD18 (LFA-1/beta 2 integrin) and CD29/CD49d (VLA-4/beta 1 integrin), respectively. TCR-directed preactivation of resting CD4+ T cells with ICAM-1 can induce increased responsiveness to B7 costimulation. In this study, we show that prior TCR-directed activation of resting CD4+ T cells with VCAM-1 induced increased responsiveness to B7 costimulation. VCAM-1 also synergized with B7 to bring about supraoptimal proliferation of CD4+ T cells. In addition, costimulation of resting T cells with VCAM-1 significantly increased not only surface expression of CD28 but also CD28-mediated mobilization of intracellular free [Ca2+]i. Similar activation of T cells with fibronectin also resulted in increased B7 responsiveness, suggesting the involvement of VLA-4 molecule. VCAM-1 costimulation induced hyperresponsiveness to B7 costimulation in both CD18+ (normal) and CD18- (leukocyte adhesion deficient) T cells. Thus, VCAM-1 may play an important costimulatory role during the activation of resting T cells and, by augmenting responsiveness to B7, facilitate optimal development of immunological memory in addition to various regulatory and effector functions.

Proliferation of human T lymphocytes induced with superantigens is not dependent on costimulation by the CD28 counter-receptor B7.

Staphylococcal enterotoxins, also known as superantigens (SAg), bind class II MHC molecules on APC and upon direct cell-to-cell contact stimulate proliferation of T cells expressing appropriate V beta gene products. The T cell surface molecule CD28 binds its costimulatory counter-receptor, B7 expressed on APC, and augments IL-2 production and T cell growth. Although the role of B7 costimulation during Ag-specific responses of T cells is established, its involvement during the activation of T cells with SAg has not been examined. Using a soluble Ig C gamma 1 chimera of CTLA-4, a second receptor for B7 and a homologue of CD28, this study examines the role of B7 expressed on APC during the induction of proliferation of CD4+ T cells upon stimulation with SAg (SAg/staphylococcal enterotoxins). CTLA-4lg, which has a higher avidity for B7 than CD28, had no effect on the synthesis of IL-2 as well as proliferative responses of CD4+ T cells induced by SAg presented on allogeneic EBV-transformed B cells, and IFN-gamma-activated endothelial cells. In contrast, T cell proliferation induced by alloAg presentation by the same APC was significantly inhibited by CTLA-4lg. mAb directed at the CD11a/CD18 molecule inhibited both SAg-induced and alloAg-induced proliferation of T cells. AlloAg-primed CD4+ T cells, which expressed both class II MHC and intercellular adhesion molecule-1 but not B7, presented SAg to and induced proliferation of both resting and SAg-primed T cells. These responses were inhibited by mAb directed at CD11a/CD18 but not by CTLA-4 Rg. These results suggest that SAg-induced responses differ from those induced by alloAg in that they are not obligatorily dependent on the costimulation by B7. In contrast, adhesive interaction between CD11a/CD18 on T cells and its counter-receptor on SAg-presenting cells is necessary and probably sufficient to support SAg-induced proliferation of T cells.

Coexpression and functional cooperation of CTLA-4 and CD28 on activated T lymphocytes.

T cell costimulation by molecules on the antigen presenting cell (APC) is required for optimal T cell proliferation. The B7 molecule on APC binds the T lymphocyte receptor CD28, triggering increased interleukin 2 (IL-2) production and subsequent T cell proliferation. CTLA-4 is a predicted T cell membrane receptor homologous to CD28, which also binds the B7 counter receptor, but whose distribution and function are unknown. Here we have developed monoclonal antibodies (mAbs) specific for CTLA-4 and have investigated these questions. mAbs were produced that bound CTLA-4 but not CD28, and that blocked binding of CTLA-4 to B7. CTLA-4 expression as measured by these mAbs was virtually undetectable on resting T cells, but was increased several hundred-fold during T cell activation. On activated lymphocytes, CTLA-4 was expressed equally on CD4+ and CD8+ T cell subsets and was coexpressed with CD25, CD28, and CD45RO. CTLA-4 expression was lower than that of CD28, reaching a maximum of approximately 1/30-50 the level of CD28. Despite its lower expression, CTLA-4 was responsible for much of the B7 binding by large activated T cells. Anti-CTLA-4 mAb 11D4 and anti-CD28 mAb 9.3 acted cooperatively to inhibit T cell adhesion to B7, and to block T cell proliferation in primary mixed lymphocyte culture. When coimmobilized with anti T cell receptor (TCR) mAb, anti-CTLA-4 mAbs were less effective than anti-CD28 mAb 9.3 at costimulating proliferation of resting or activated T cells. However, coimmobilized combinations of anti-CD28 and anti-CTLA-4 were synergistic in their ability to augment anti-TCR-induced proliferation of preactivated CD4+ T cells. These results indicate that CTLA-4 is coexpressed with CD28 on activated T lymphocytes and cooperatively regulates T cell adhesion and activation by B7.

Differential regulatory effects of intercellular adhesion molecule-1 on costimulation by the CD28 counter-receptor B7.

Although ligation of the CD3/TCR complex initiates an activation signal in T cells, additional costimulatory signals generated during cell-to-cell interactions with APC transduced via ligation of CD11a/CD18 and CD28 by their specific counter-receptor intercellular adhesion molecule (ICAM)-1 and B7, respectively, are required for optimal T cell proliferation and cytokine synthesis. Using soluble IgC gamma 1 fusion proteins of these costimulatory counter-receptors, we have recently shown that unactivated resting CD4+ T cells and Ag-primed CD4+ T cells differ in their response to the costimulation by ICAM-1 and B7. Preferential proliferative responses of resting T and Ag-primed T cells to ICAM-1 and B7, respectively, prompted us to speculate that ICAM-1-induced signals may regulate coupling of the CD28 signaling pathway. Furthermore, both B7 and ICAM-1 are co-expressed on APC and thus, may co-regulate activation-driven maturation of T cells. In this study, we have examined regulatory effects of IgC gamma 1 fusion proteins of B7, ICAM-1, and ICAM-2 (a homologue of ICAM-1) on each other's costimulation. We first demonstrate that TCR-directed costimulation of resting CD4+ T cells with ICAM-1 (ICAM-1 priming) but not ICAM-2 induces increased responsiveness to B7. Priming of CD4+ T cells with ICAM-1 induced higher expression of both CD18 and CD28 than that with either B7 or ICAM-2. Cross-linking of CD28 induced faster and significantly higher cytoplasmic free calcium mobilization response in ICAM-1-primed CD4+ T cells than in resting, B7-primed, or ICAM-2-primed CD4+ T cells. B7 synergized with ICAM-1 but not ICAM-2 to augment proliferative responses of not only resting CD4+ T cells but also those that had been primed with either ICAM. Unlike resting or ICAM-2-primed CD4+ T cells, ICAM-1-primed CD4+ T cells efficiently proliferated in response to the synergistic costimulation of B7 and ICAM-2. In contrast, both ICAM-1 and ICAM-2 inhibit B7-driven proliferation of Ag-primed CD4+ T cells. Thus, B7 and ICAM-1 exert contrasting regulatory effects on the proliferation of CD4+ T cells depending on their state of activation-induced maturation.

GMP-140 (P-selectin/CD62) binds to chronically stimulated but not resting CD4+ T lymphocytes and regulates their production of proinflammatory cytokines.

GMP-140 (P-selectin), a 140-kDa granular membrane glycoprotein localized to the alpha granules of platelets and the Weibel-Palade bodies of endothelial cells, is thought to play an important role in adhesive interactions predominantly between granulocytes, platelets and vascular endothelial cells during inflammation. Although GMP-140 binds to granulocytes, its binding to lymphocytes has not been demonstrated. Using genetically engineered IgG C gamma 1 fusion protein of the extracellular domains of GMP-140, we demonstrate that GMP-140 binds to chronically antigen (Ag)-stimulated CD4+ T cells. Freshly isolated CD4+ T cells did not bind GMP-140, but priming and subsequent stimulation with alloantigen induced and gradually increased expression of GMP-140-reactive structures on their surface. T cells isolated from rheumatoid synovial fluids also exhibited strong binding to GMP-140. The binding of GMP-140 to primed T cells is not influenced by preactivation with phorbol 12-myristate 13-acetate, is almost completely abolished by pretreatment of T cells with neuraminidase or trypsin, and is also strongly inhibited by EDTA, the soluble sulfated glycans dextran sulfate, fucoidan, and heparin, but not by chondroitin sulfates. In spite of its strong binding to Ag-primed T cells, GMP-140 did not modulate the proliferative responses of these cells to various stimuli. However, GMP-140 in conjunction with anti-T cell receptor alpha beta monoclonal antibodies augmented the production of granulocyte-macrophage colony-stimulating factor GM-CSF and inhibited the production of interleukin-8 by Ag-primed T cells without influencing their tumor necrosis factor-alpha production. These results suggest that GMP-140 binds to chronically stimulated CD4+ T cells and differentially modulates their production of proinflammatory cytokines. The ability of Ag-primed T cells to bind GMP-140 may facilitate interactions with activated platelets and endothelial cells affecting the course of inflammation.

Differential costimulatory effects of adhesion molecules B7, ICAM-1, LFA-3, and VCAM-1 on resting and antigen-primed CD4+ T lymphocytes.

Optimal proliferation of T cells although initiated via ligation of the CD3/TCR complex requires additional stimulation resulting from adhesive interactions between costimulatory receptors (R) on T cells and their counter-R on APC. At least four distinct adhesion molecules (counter-R) present on APC, B7, ICAM-1 (CD54), LFA-3 (CD58), and VCAM-1 have been individually shown to costimulate T cell activation. Because some of these molecules may be expressed simultaneously on APC, it has been difficult to examine relative contributions of individual counter-R during the induction of T cell proliferation. We have produced soluble IgC gamma 1 fusion chimeras (receptor globulins or Rg) of B7, ICAM-1, LFA-3, and VCAM-1 and compared their relative abilities to costimulate proliferation of resting or Ag-primed CD4+ T cells. When co-immobilized with mAb directed at TCR alpha beta or CD3 but not CD2 or CD28, each Rg induced proliferation of both resting and Ag-primed CD4+ cells. In contrast, similarly co-immobilized CD7 Rg or ELAM-1 Rg were ineffective. Resting CD4+ T cells produced more IL-2, expressed significantly higher levels of IL-2R alpha, and proliferated more efficiently when costimulated with either ICAM-1 Rg or VCAM-1 Rg than with B7 Rg or LFA-3 Rg. CD4+ CD45RO+ memory T cells proliferated more vigorously in response to the costimulation by each of the four Rg than CD4+ CD45RA+ naive T cells. In contrast with the behavior of resting CD4+ T cells, proliferation of Ag-preactivated CD4+ T cells was most efficient when costimulated by B7 Rg. The costimulatory effect of LFA-3 Rg on Ag-primed CD4+ T cells was weaker than that of B7 Rg but was significantly greater than that of either ICAM-1 Rg or VCAM-1 Rg. These results suggest that resting and Ag-primed CD4+ T cells preferentially respond by proliferation to different costimulatory counter-R. ICAM-1 and VCAM-1 may be involved in the initiation of proliferation of Ag-responsive T cells, and B7 and LFA-3 may facilitate sustained proliferation of Ag-primed T cells. The cumulative costimulation by the above counter-R may facilitate optimal expression of various regulatory and effector functions of T cells.