Soluble CD40 ligand impairs the anti-platelet function of peripheral blood angiogenic outgrowth cells via increased production of reactive oxygen species

Adult peripheral blood angiogenic early outgrowth cells (EOCs), also known as early endothelial progenitor cells, interact with other blood and vascular cells and may regulate atherothrombosis. We have previously shown that endothelial progenitor cells inhibit platelet function and thrombus formation. The CD40L/CD40 axis is a thrombo- inflammatory mediator that affects platelet and endothelial functions. It has been shown that EOCs express CD40, whereas platelets represent the major source of its soluble ligand (sCD40L), which impairs EOC function.We aimed to test the hypothesis that the sCD40L/CD40 axis affects the anti-platelet function of EOCs. Human peripheral blood mononuclear cell-derived EOCs in culture inhibited platelet aggregation. Pre-treatment of EOCs with sCD40L reduced their inhibitory effect on platelet aggregation in a CD40-dependent manner. EOCs viability and release of the anti-aggregating agents, prostacyclin and nitric oxide, were not affected by sCD40L. However, production of reactive oxygen species (ROS) was increased in sCD40L-treated EOCs. Blockade of ROS reversed the effects of sCD40L-treated EOCs on platelet aggregation. This study reveals that the sCD40L/CD40 axis impairs the anti-platelet properties of EOCs through increased production of ROS. These data may explain the link between elevated levels of sCD40L, impaired activity of EOCs and enhanced platelet reactivity, and consequently the occurrence of atherothrombotic disease.

Use of transesophageal Doppler as a sole cardiac output monitor for reperfusion hemodynamic changes during living donor liver transplantation: An observational study

Aims:

To report the use of transesophageal Doppler (TED), a minimally invasive cardiac output (COP) monitor, before, during and after reperfusion and study its effect on anesthetic management during living donor liver transplantation (LDLT).

Setting and Design:

A prospective observational study.

Methods:

A total of 25 consecutive recipients with a MELD score between 15 and 20 were enrolled. Data were recorded at baseline (TB); anhepatic phase (TA); and post-reperfusion — 1, 5, 10 and 30 minutes. Fluid therapy was guided by corrected flow time (FTc) of the TED. Packed red blood cells (RBCs) were only given when hematocrit was less than 25%. Rotational thromboelastometry (ROTEM) and standard laboratory tests were used to guide component blood products requirements.

Results:

Post-reperfusion, the COP, Cardiac Index (CI) and stroke volume (SV) increased significantly at all points of measurements; this was associated with a significant decrease in systemic vascular resistance (SVR) (P ;< .05). Immediately post-reperfusion, for 5 minutes, mean arterial blood pressure (ABP) dropped significantly (P < .05), and 14 out of the 25 patients required boluses of epinephrine (10 μg) to restore the mean ABP; 3 of the 14 patients required norepinephrine infusion till the end of surgery. Central venous pressure (CVP) and urine output (UOP) at all measures were maintained adequately with FTc-guided fluid replacement. Eight out of the 25 patients required no blood transfusion, and 4 of the 8 patients required no catecholamine support.

Conclusion:

TED as a sole monitor for COP was able to present significant and reliable changes in the cardiovascular status of the recipients during reperfusion, which could help to guide fluid- and drug-supportive therapy in this population of patients. This preliminary study needs to be applied on a larger scale.

Intravenous immunoglobulin attenuates airway hyperresponsiveness in a murine model of allergic asthma

BACKGROUND

Intravenous immunoglobulin (IVIG) has potent anti-inflammatory and immune-modulating properties. IVIG has been utilized as a steroid-sparing agent in severe asthma, but the results of clinical trials have been conflicting.

OBJECTIVE

To determine whether IVIG is able to attenuate bronchial reactivity, pulmonary inflammation and T cell function using a murine model of allergic airways disease.

METHODS

BALB/c or C57BL/6 mice were sensitized to ovalbumin (OVA) or a phosphate-buffered saline control using local nasal sensitization, and then received five intranasal challenges on days 28-32 before sacrifice. Mice were treated intraperitoneally with either IVIG (1-2 g/kg) or equivalent human serum albumin 24 h before the first OVA challenge. Bronchial reactivity to methacholine was examined using the FlexiVent small animal ventilator. We evaluated pulmonary histology, mRNA from lung digests for T-helper type 2 (Th2)-related genes and bronchoalveolar lavage for cell counts and cytokines. Splenocytes were utilized to study OVA-induced cell proliferation, cytokine production and dendritic cell maturation.

RESULTS

IVIG markedly attenuated the perivascular and peribronchial pulmonary inflammation, and decreased bronchial hyperresponsiveness to methacholine. IVIG treatment of splenocytes from sensitized animals diminished cellular proliferation to OVA, whereas IVIG treatment in vivo markedly attenuated OVA-driven splenocyte proliferation. This is accompanied by diminished IL-13 and TNF-α levels in splenocyte culture, decreased expression of Jagged-1, increased Delta-4 and decreased GATA-3 mRNA levels, signs that IVIG has suppressed the expected Th2 response that accompanies repeated allergen exposure. Increased regulatory T cells were found in draining pulmonary lymph nodes in IVIG-treated mice but not in controls.

CONCLUSIONS AND CLINICAL RELEVANCE

IVIG was effective in ameliorating allergic airway disease in our model. IVIG may be a promising adjunct therapy requiring further study for patients with severe asthma.

Dermatologic complications after liver transplantation: a single-center experience

OBJECTIVE

To report our experience with dermatological complications after both deceased donor liver transplantation (DDLT) and living-donor liver transplantation (LDLT).

PATIENTS AND METHODS

Between April 2001 and November 2006, a total of 116 liver transplantation (LT) procedures were performed (73 DDLTs and 43 LDLTs) in 112 patients (4 re-transplants). Posttransplant dermatological problems were recorded.

RESULTS

Among 112 OLT recipients, 14 patients (12.5%) experienced dermatologic problems: epidermolysis bullosa acquisita in one patient, which was self-limiting; graft-versus-host-disease in one patient treated with high-dose steroids; Kaposi sarcoma in one patient treated with surgical excision and conversion to sirolimus-based immunosuppression; drug-induced cutaneous vasculitis with deep thigh ulcer formation treated by drug discontinuation and surgical excision of the ulcer; herpes zoster in one patient treated with intravenous antiviral therapy; herpes simplex in two patients treated with local antiviral cream; cyclosporine-induced gingival hyperplasia treated with conversion to FK506; cyclosporine-induced hypertrichosis treated with conversion to FK506; steroid-induced skin hyperpigmentation in one patient treated with steroid withdrawal; hypomagnesemia-induced hair loss treated with daily oral magnesium supplement; pressure-induced alopecia areata in two patients that was self-limiting; and finally, one patient with a pressure-induced heel ulcer that was treated conservatively. In 8 of 14 patients (57%) who suffered from dermatologic problems, the complication was primarily related to immunosuppressive drugs.

CONCLUSIONS

In our experience, dermatologic complications following LT are not uncommon and usually related to immunosuppressive therapy. Most complications could be prevented by optimizing immunosuppression. The majority of complications were easily managed by simple adjustment of immunosuppression.

Liver transplantation for autoimmune hepatitis: a single-center experience

OBJECTIVE

To present our experience with deceased donor liver transplantation (DDLT) and living-donor liver transplantation (LDLT) for autoimmune hepatitis (AIH).

PATIENTS AND METHOD

Between April 2001 and November 2006, a total of 116 LT procedures were performed (73 DDLTs and 43 LDLTs) in 112 patients (4 retransplants). Of the 112 recipients, 16 patients (14.3%) were transplanted for AIH (15 DDLTs and 1 LDLT). All recipients received FK506- and steroid-based immunosuppressive regimens.

RESULTS

The male/female ratio was 3/13, median age was 22 years (range, 15 to 35), and the median MELD score was 25 (range, 11 to 40). Arterial reconstruction was needed in four DDLTs due to severe steroid-induced angiopathy. After a median follow-up period of 530 days (range, 11 to 2016), the overall patient and graft survival rates were 93.8%. Only one patient died following LDLT due to primary graft nonfunction. Histopathologic recurrence was seen in three patients (18.7%) and was successfully treated by optimizing immunosuppression. Markedly elevated serum CA19-9 levels (median, 1069; range, 217 to 2855) was seen in four patients (28%), malignancy was ruled out and all patients normalized serum CA19-9 levels within the first 3 months posttransplant. Steroids withdrawal failed in all recipients and was always accompanied with almost immediate elevation of liver enzymes.

CONCLUSIONS

In our experience, LT for AIH shows excellent long-term outcomes, patients are usually young women who present with acute deterioration and high MELD scores, and usually require long-term steroids to prevent rejection and disease recurrence. Some patients have markedly high CA19-9 in absence of malignancy. Some patients also have severe steroid-induced hepatic artery angiopathy necessitating arterial reconstruction during the transplant surgery.

The value of CD34, myeloperoxidase and chloroacetate esterase (Leder) stain in the diagnosis of granulocytic sarcoma

BACKGROUND

The differentiation of extramedullary myelogenous leukemia/granulocytic sarcoma (GS) from malignant lymphoma can sometimes be difficult. In the current study, we explored the value of CD34, myeloperoxidase and nonspecific esterase (Leder) stains in differentiating GS from lymphomas.

MATERIALS AND METHODS

Fifteen cases of phenotypically confirmed GS were stained for CD34, myeloperoxidase and Leder stains. The same stains were performed in 16 malignant lymphomas as controls. The GS cases were also immunostained for CD3 and CD20 to detect the incidence of aberrant T and B lymphocyte expression.

RESULTS

CD34 was expressed in 7 of the 15 cases of GS (46%). Myeloperoxidase was expressed in 10 of the 15 cases (66%), and Leder stain was positive in 9 cases (60%). All 15 cases had expression of at least one marker; 8 cases had expression of two markers and one case had expression of all 3 markers. None of the lymphomas showed expression of any of the three markers. Five cases (35%) of GS showed T cell antigen expression and 2 (14%) showed B cell antigen expression.

CONCLUSION

Our findings suggest that in cases of GS, the use of the combination of CD34, myeloperoxidase and Leder stains can help reach a definitive diagnosis, especially if lymphoma is difficult to exclude. Expression of B and T cell antigens in such lesions should not rule out the diagnosis of GS.

Leishmania donovani-induced macrophages cyclooxygenase-2 and prostaglandin E2 synthesis

Prostaglandin E2 (PGE2) secretion during Leishmania infection has been reported. However, the signalling mechanisms mediating this response are not well understood. Since cyclooxygenase-2 (COX-2) and cytosolic phospholipase A2 (cPLA2) are involved in PGE2 synthesis in response to various stimuli, the implication of these enzymes was evaluated in Leishmania-infected phorbol myristate acetate-differentiated U937 human monocytic cell line. Time-course experiments showed that PGE2 synthesis increased significantly in parallel with COX-2 expression when cells were incubated in the presence of Leishmania donovani promastigotes or lipopolysaccharides (LPS). Increase in cPLA2 mRNA expression was only detected when cells were stimulated with LPS. Indomethacin, genistein, and H7, which are antagonists of COX-2, protein tyrosine kinase (PTK) and protein kinase C (PKC), respectively, inhibited PGE2 production induced by L. donovani and LPS. However, only H7 inhibited COX-2 mRNA synthesis, and there was a significant correlation between PGE2 inhibition and reduced COX-2 expression. Collectively, our results indicate that infection of U937 by L. donovani leads to the generation of PGE2 in part through a PKC-dependent signalling pathway involving COX-2 expression. They further reveal that PTK-dependent events are necessary for Leishmania-induced PGE2 generation, but not for COX-2 expression. A better understanding of the mechanisms by which Leishmania can induce PGE2 production could provide insight into the pathophysiology of leishmaniasis and may help to improve therapeutic approaches.

Early stage carcinoma of oral tongue: prognostic factors for local control and survival

The purpose of this study was to assess prognostic factors, treatment outcomes and patterns of relapse in patients with early stage (T1-2 N0) squamous cell carcinoma of oral tongue treated primarily by surgery. The medical records of all patients with early stage (T1-2 N0) oral tongue cancer, radically treated at King Faisal Specialist Hospital and Research Center between January 1980 and December 1997, were reviewed. Eighty-five patients were identified for analysis, 38 male and 47 female. With a median follow-up for surviving patients of 64 months, 5-year actuarial overall, disease-specific (DSS), and relapse-free survival (RFS) were 71, 75, and 63%, respectively. Univariate analysis for DSS showed survival advantage for patients with tumor thickness (TT) of < or =10 mm (P=0.0002) and distance from resection margin (DFRM) of > 5 mm (P=0.005). The effect of TT of < or =10 mm was maintained (P=0.001) on multivariate analysis. Higher RFS was observed with TT of < or =10 mm (P=0.0002), DFRM of > 5 mm (P=0.0002) and DFRM of >10 mm (P=0.007). On multivariate analysis higher RFS was also found for TT < or =10 mm (P=0.01) and DFRM >5 mm (P=0.01). Salvage of local tongue recurrence was higher than neck node failure, with 5-year DSS of 71 and 19%, respectively (P=0.007). Time interval for recurrence showed no significant impact on outcome. In T1-2 N0 oral tongue cancer, TT, and DFRM are significant prognostic factors for both local control and survival. Neck node recurrence is associated with poor prognosis and low salvage rate.

Ovarian hormones modulate monocyte chemotactic protein-1 expression in endometrial cells of women with endometriosis

Endometriosis, a frequent oestrogen-dependent disease believed to result from an aberrant proliferation of endometrial tissue outside the uterine cavity, is associated with an increased expression of monocyte chemotactic protein-1 (MCP-1) in the intrauterine endometrium. This makes it plausible that migrating endometrial cells are intrinsically able to initiate monocyte chemoattraction and activation, a phenomenon which has been consistently observed in the peritoneal cavity of patients and recently in their eutopic endometrium. To elucidate the mechanisms involved in the regulation of MCP-1 expression in eutopic endometrial cells, we studied the effects of ovarian hormones and found that oestradiol (10(-9) and 10(-8) mol/l) markedly increased MCP-1 mRNA steady-state levels and protein secretion by endometrial cells in response to interleukin-1beta (IL-1beta) (0.1 ng/ml). The IL-1beta-induced MCP-1 expression was even higher following pretreatment of cells with both oestradiol (10(-9) mol/l) and progesterone (5x10(-8) mol/l). This did not seem to be due to increased MCP-1 mRNA stability, but rather to a higher level of gene transcription. Our results provide evidence that ovarian steroids regulate, indirectly, the synthesis and the secretion of a potent chemotactic and activating factor for monocytes/macrophages by endometrial cells of women with endometriosis and reveal a new mechanism for oestradiol action.

Binding of Mycoplasma arthritidis-derived mitogen to human MHC class II molecules via its N terminus is modulated by invariant chain expression and its C terminus is required for T cell activation

Mycoplasma arthritidis-derived mitogen (MAM) is considered to be a member of the super-antigen family despite the fact that there is no evidence until now indicating its binding to MHC class II molecules. To demonstrate its direct binding and to determine the regions involved in MHC class II and TCR interactions, we generated a recombinant wild-type and two truncated forms of the MAM protein. Data obtained in the course of the present investigation show that MAM binds specifically and significantly to human MHC class II molecules. Evidence is also provided that MAM bears two distinct binding regions: one is located within its N terminus and interacts with MHC class II molecules, while the second region which is located in its C terminus mediates its recognition by the TCR. Association of the MHC class II-associated invariant chain peptide with the peptide binding groove on the cell surface completely abolished MAM binding and presentation. This inhibitory effect is restored by the expression of HLA-DM molecules, suggesting that the nature of the peptide within the binding groove and/or the stability of the MHC class II molecules on the cell surface may modulate MAM/MHC class II interactions.

CD40 associates with the MHC class II molecules on human B cells

The MHC class II and CD40 molecules are two major components of the immune system that are involved in cell-cell interactions and signal transduction. Data obtained in the course of the present investigation show that these two molecules are physically associated on the surface of various human B cell lines and on normal tonsilar B cells. The CD40 / MHC class II complexes were not detected on the germinal center B cell line Ramos. However, stimulation of these cells via CD40 or MHC class II triggered their association, suggesting that the formation of the complex is related to the activation status of the cells. The formation of these complexes did not alter the interaction of MHC class II molecules with one of their natural ligands, the staphylococcal enterotoxin A (SEA), as evidenced by the ability of SEA to bind MHC class II / CD40 complexes. Cross-linking of MHC class II or CD40 molecules leads to the association as well as the co-association of both molecules to the NP-49-insoluble cellular matrix. Such association allowed us to demonstrate that only a fraction of these molecules can be physically associated on the cell surface. Based on previous observations and those presented here, it is highly possible that the CD40 / MHC class II complexes may have an important role in signal(s) induced via both molecules and during T / B cells interactions.

Fine-needle aspiration biopsy diagnosis of small round cell tumors of childhood: A comprehensive approach

Fine-needle aspiration biopsy findings in small round cell malignant tumors of children are briefly reviewed. All of these tumors usually have characteristic cytomorphology which, when recognized, may lead to a definitive diagnosis. However, when these tumors are undifferentiated, morphologic criteria may not be sufficient for arriving at a correct diagnosis. A variety of ancillary studies including electron microscopy, immunohistochemistry and DNA ploidy, cytogenetics, and fluorescent in situ hybridization may provide valuable additional information for precise characterization of these neoplasms. Some of the ancillary studies may also be used for assigning these cases to prognostically significant subgroups. This information may also help in defining the most suitable chemotherapeutic regimens for these tumors. Since most of these special studies require only a small amount of cellular material, fine-needle aspiration biopsy is ideally suited for obtaining samples for these procedures. It is hoped that as cytogenetic and molecular techniques become available in many diagnostic laboratories, a comprehensive evaluation of aspiration biopsies from round cell malignant tumors, encompassing a precise pathologic diagnosis, determination of prognosis, and prediction of response to therapy, will be possible in a majority of cases. Diagn. Cytopathol. 1999;21:81-91.

CD40- and HLA-DR-mediated cell death pathways share a lot of similarities but differ in their use of ADP-ribosyltransferase activities

CD40 and HLA-DR molecules are two major components of the immune system, and their engagement on several cell types leads to various cellular events that modulate cell function. In this study, we demonstrate that signaling via these molecules leads to a rapid B cell death. CD40-mediated cell death was mainly observed in Epstein-Barr virus (EBV)-transformed B cell lines, whereas, HLA-DR-induced response can be triggered in normal activated B cells as well as in EBV-transformed B cell lines. Cell death induced via both molecules does not require de novo protein synthesis, but involves the integrity of the cytoskeleton. The sensitivity of CD40- and HLA-DR-mediated cell death to various inhibitors is very similar to that previously reported for tumor necrosis factor receptor (TNFR)- and Fas-triggered apoptosis; however, caspases leading to poly(ADP-ribose) polymerase cleavage are not implicated in this response. Both B cell death forms do not involve Fas-Fas ligand and TNF-TNFR systems, but require LFA-1-independent cell-cell interactions mediated by still undefined molecules. Although CD40- and HLA-DR-mediated cell death appears to follow a common pathway, inhibitors of poly- and mono-ADP-ribosyltransferase activity differentially affect these responses. Defining the molecules involved in CD40- and HLA-DR-mediated death will provide a possible interrelation between the different B cell death programs that can lead to a better comprehension of regulation of B cell functions.

Ligation of MHC class II molecules differentially upregulates TNF beta gene expression in B cell lines of different MHC class II haplotypes

Although the production of selected cytokines by B cells is important for their regulation, little is known about MHC class II-induced cytokine expression in these cells. We designed the present studies to investigate MHC class II-mediated TNF-beta gene expression in 19 EBV-transformed homozygote B cell lines at similar stage of differentiation but presenting different MHC class II haplotypes. Our results demonstrate that in contrast to PMA, engagement of MHC class II with staphylococcal enterotoxin A (SEA), a natural ligand, or with anti-HLA-DR mAb L243, stimulates TNF-beta gene expression in some but not all B cell lines. The differential stimulation of TNF-beta gene expression via MHC class II was not due to the cells MHC class II expression level, nor to their capacity to bind the ligands as evidenced by SEA binding affinity studies. Together these results demonstrate that ligation of MHC class II molecules can stimulate TNF-beta gene expression in a B cell line-dependent manner. The differential cytokine gene expression might be due to an influence of MHC class II haplotype either by a linkage disequilibrium with TNF-beta gene or by a differential association with effector or cell surface molecules.

Triggering HLA-DR molecules on human peripheral monocytes induces their death

Although engagement of MHC class II molecules on human monocytes triggers various cellular events, their possible role in monocyte death is yet unknown. We demonstrate that ligation of MHC class II on primary monocytes induces a rapid cell death that has all the characteristics of monocyte apoptosis, does not require de novo protein synthesis, is independent from both Fas and TNF-alpha systems, and is not rescued by ligation of CD40. However, cell-cell interactions that involve the beta2-integrin CD18 seem to be critical for the execution of this monocyte death. Priming monocytes with IFN-gamma enhances significantly their HLA-DR-mediated death whereas LPS treatment effectively reverses this death process. Thus, our results describe the MHC class II molecules, in particular HLA-DR, as mediators of monocyte death and suggest that this novel pathway of monocyte death might have an important role in controlling the outcome of inflammatory process and the regulation of monocyte hemostasis.

CD20 is physically and functionally coupled to MHC class II and CD40 on human B cell lines

Engagement of MHC class II and CD40 on B cell lines triggers intracellular signals that activates cell surface adhesion receptors, resulting in LFA-1-dependent and -independent cell-cell adhesion. In this study, a murine monoclonal antibody (mAb R21) has been produced against a LFA-1-negative human B cell line and proven to completely block MHC class II- and CD40-induced LFA-1-independent homotypic adhesion. However, this mAb failed to prevent MHC class II- or CD40-induced homotypic adhesion in LFA-1-positive Raji B cells, and alone, it triggered LFA-1-dependent cell-cell adhesion. Biochemical characterization indicated that the CD20 molecule, a tetraspan phosphoprotein expressed on B cells that functions as a Ca2+-conductive ion channel, is the target of mAb R21. Interestingly, further biochemical analysis demonstrated that CD20 is physically associated with MHC class II and CD40 molecules on the cell surface of LFA-1-negative and LFA-1-positive B cell lines. Although these three molecules are associated with each other, the complex formation between any two of them is not dependent on the simultaneous expression of the three molecules. Altogether, these results indicate that CD20 is physically and probably functionally coupled to the MHC class II and CD40 molecules; thereby it may have certain modulatory effects on their functions.

Expression of functional major histocompatibility complex class II molecules on HMC-1 human mast cells

Mast cells hold a key position in the defensive mechanisms against exogenous intruders. In this study, we investigated whether human mast cells express functional major histocompatibility complex (MHC) class II molecules that can transduce endogenous signals and present staphylococcal enterotoxin A (SEA) to T cells. Similar to HMC-1 human mast cell line, umbilical cord blood-derived mast cells express HLA-DR, -DP and -DQ molecules on their surface. MHC class II molecules expressed on HMC-1 cells bind significantly the SEA (a natural MHC class II ligand), and their ligation with specific mAbs or with SEA, leads ultrastructural changes, suggesting their degranulation. Recognition of SEA-bound MHC class II molecules on HMC-1 mast cells by the T cell receptor of K25 cells, an SEA-specific murine T cell hybridoma, triggers significant IL-2 secretion by these T cell hybridomas. Hence, our data point out the expression of functional MHC class II molecules on human mast cells, reinforcing the implication of these cells in the defense mechanisms of acquired immunity.

Epstein-Barr virus expression in Hodgkin's disease: Correlation with histologic subtypes and T and B lymphocyte distribution

BACKGROUND

The pathogenesis of Hodgkinâs disease (HD) has been linked to Epstein-Barr virus (EBV). Some histologic subtypes show a high level of viral expression. These include mixed cellularity (MCHD) and nodular sclerosis (NSHD) subtypes. Grade II NSHD is a more aggressive variant of HD. Lymphocyte predominant (LPHD) is a B cell lymphoproliferative disorder that has not been associated with EBV expression. Infiltrating lymphocytes in HD are predominantly T lymphocytes, with a minor component of B lymphocytes. In the current study, EBV expression was tested in cases of HD in relation to histologic subtypes. An attempt was made at correlating EBV expression with T and B lymphocyte distribution in lymph nodes involved by HD.

METHOD

Formalin-fixed paraffin-embedded tissue from 62 cases of HD were tested for EBV mRNA expression, using the EBER-1 probe and in situ hybridization. T and B lymphocyte distribution and their ratios were evaluated using antibodies to T and B lymphocytes (UCHL-1 [CD45 RO] and CD 20, respectively), and the immunoperoxidase technique.

RESULTS

The cases were seen in 38 male and 24 female patients, with an age range of 3 to 72 years (median 25 years). There were 30 cases of grade I and 15 cases of grade II NSHD, 9 cases of MCHD and 8 cases of LPHD. EBV mRNA expression was seen in 29 cases (46%). This expression was seen in 8 cases of grade I NSHD (26%), 13 cases of grade II NSHD (86%) and 8 cases of MCHD (88%). None of the cases of LPHD showed viral expression. T to B lymphocyte ratios in EBV-positive cases ranged from 1/6 to 8/1, and ranged from 2/1 to 20/1 in EBV-negative cases (P=0.06). Nine of the 29 positive cases (31%) showed equal T/B lymphocyte ratios (n=4), or predominance of B lymphocytes (n=5). None of the EBV-negative cases showed predominance of B lymphocytes.

CONCLUSION

Our study confirms previously reported findings of the prevalence of EBV expression in MCHD and NSHD. Our findings also suggest that EBV expression may be more commonly seen in aggressive forms of HD. Decreased numbers of T lymphocytes in these aggressive subtypes may suggest that a process of more profound T lymphocyte depletion is occurring in these cases, leading to uncontrolled EBV replication and more aggressive disease.

IL-4 mRNA transcription is induced in mouse bone marrow-derived mast cells through an MHC class II-dependent signaling pathway

We have previously shown that mouse bone marrow-derived mast cells (BMMC) can process and present immunogenic peptides to CD4 T cells. Here, we report on a T cell-dependent MHC class II-mediated mast cell activation resulting in IL-4 transcription and protein release. Presentation of optimal doses of ovalbumin peptide 323-339 resulted in IL-2 production by a specific T cell hybridoma and increase in IL-4 mRNA transcription in mast cells. IL-4 mRNA transcription increased by 200-fold in mast cells treated in IL-3/IL-4/granulocyte-macrophage colony-stimulating factor (high presenters) whereas only a tenfold increase or no increase were obtained with IL-3/IL-4/IFN-gamma- or IL-3-treated mast cells (low presenters), respectively. Induction of IL-4 mRNA transcription in purified mast cells by direct ligation of MHC class II molecules, using anti-I-A and anti-I-E-coated beads, indicates that MHC class II molecules are critical in this signaling pathway. However, when compared to T cells, anti-MHC class II-coated beads were less efficient, indicating a potential role of accessory molecules in this mast cell activation process. IgE-independent IL-4 production by mast cells as a result of cognate interaction with CD4 T cells could be critical for the development of type 2 responses. This novel mechanism may contribute to the induction and/or amplification of specific IgE-mediated allergic responses.

Staphylococcal enterotoxin D is a promiscuous superantigen offering multiple modes of interactions with the MHC class II receptors

Dimerization of MHC class II molecules on the cell surface of human THP-1 monocytic cell line is a requirement for staphylococcal superantigen (SAG)-induced cytokine gene expression. The capacities of various SAG to induce this response are governed by their modes of interaction with MHC class II molecules. Staphylococcal enterotoxin A (SEA), with its two binding sites, dimerizes MHC class II molecules and subsequently induces cytokine gene expression in THP-1 cells. Here, we demonstrate that staphylococcal enterotoxin D (SED) and staphylococcal enterotoxin E (SEE) induce, similarly, IL-1beta and TNF-alpha gene expression in these cells. Using mutated toxins that lost their binding site with the MHC class II alpha- or beta-chain, we demonstrate that this response is also mediated by the dimerization of MHC class II molecules through two binding sites. Furthermore, SED forms Zn2+-dependent homodimers that allow multiple modes of MHC class II clustering, including ligation of alpha-chains (alpha/alpha), beta-chains (beta/beta), or the alpha- and beta-chains of two different class II molecules. The beta/beta interaction following Zn2+-dependent SED/SED homodimer formation seems to be mediated by the appearance of a novel binding site on SED that interacts with histidine 81 of the MHC class II beta-chain. The different modes of SED interactions also influence SED-induced T cell activation where simultaneous ligation of the alpha- and beta-chains is essential for optimal response. These various modes of SED binding may be used to preserve bivalency regardless of variability in the MHC class II alpha/beta/peptide complexes.

Functional analysis of Mycoplasma arthritidis-derived mitogen interactions with class II molecules

The ability of superantigens (SAGs) to trigger various cellular events via major histocompatibility complex (MHC) class II molecules is largely mediated by their mode of interaction. Having two MHC class II binding sites, staphylococcal enterotoxin A (SEA) is able to dimerize MHC class II molecules on the cell surface and consequently induces cytokine gene expression in human monocytes. In contrast, cross-linking with specific monoclonal antibodies or T-cell receptor is required for staphylococcal enterotoxin B (SEB) and toxic shock syndrome toxin 1 (TSST-1) to induce similar responses. In the present study, we report how Mycoplasma arthritidis-derived mitogen (MAM) may interact with MHC class II molecules to induce cytokine gene expression in human monocytes. The data presented indicate that MAM-induced cytokine gene expression in human monocytes is Zn2+ dependent. The MAM-induced response is completely abolished by pretreatment with SEA mutants that have lost their capacity to bind either the MHC class II alpha or beta chain, with wild-type SEB, or with wild-type TSST-1, suggesting that MAM induces cytokine gene expression most probably by inducing dimerization of class II molecules. In addition, it seems that SEA and MAM interact with the same or overlapping binding sites on the MHC class II beta chain and, on the other hand, that they bind to the alpha chain most probably through the regions that are involved in SEB and TSST-1 binding.

Molecular characterization and role in T cell activation of staphylococcal enterotoxin A binding to the HLA-DR alpha-chain

Superantigens bind to MHC class II-positive cells and stimulate T lymphocytes expressing specific V beta regions of the TCR. Two distinct regions of staphylococcal enterotoxin A superantigen (SEA) have been shown to affect the binding to MHC class II molecules. Results presented here demonstrate for the first time that the SEA-DR interaction can be affected by mutations on the class II alpha-chain. Furthermore, we have precisely mapped the interaction of the SEA N-terminal domain with the alpha1 domain of HLA-DR. Scatchard analysis using DAP cells transfected with mutant class II molecules showed a role for residue DR alpha K39 in the binding of SEA. Also, complementation experiments using mutant SEA molecules revealed an interaction between SEA residue F47 and position alphaQ18 on an outer loop of HLA-DR. These interactions between SEAF47 and the DR alpha-chain are critical, as they allow the recognition by an otherwise nonreactive V beta1+ T cell hybridoma and induction of tyrosine phosphorylation through the TCR.

Molecular characterization and role in T cell activation of staphylococcal enterotoxin A binding to the HLA-DR alpha-chain

Superantigens bind to MHC class II-positive cells and stimulate T lymphocytes expressing specific V beta regions of the TCR. Two distinct regions of staphylococcal enterotoxin A superantigen (SEA) have been shown to affect the binding to MHC class II molecules. Results presented here demonstrate for the first time that the SEA-DR interaction can be affected by mutations on the class II alpha-chain. Furthermore, we have precisely mapped the interaction of the SEA N-terminal domain with the alpha1 domain of HLA-DR. Scatchard analysis using DAP cells transfected with mutant class II molecules showed a role for residue DR alpha K39 in the binding of SEA. Also, complementation experiments using mutant SEA molecules revealed an interaction between SEA residue F47 and position alphaQ18 on an outer loop of HLA-DR. These interactions between SEAF47 and the DR alpha-chain are critical, as they allow the recognition by an otherwise nonreactive V beta1+ T cell hybridoma and induction of tyrosine phosphorylation through the TCR.

The crystal structure of staphylococcal enterotoxin type D reveals Zn2+-mediated homodimerization

Bacterial superantigens, including the staphylococcal enterotoxins, are the most potent activators of T cells known and have been suggested as a causative factor in Gram-positive shock in humans. Staphylococcal enterotoxin D (SED) is dependent upon Zn2+ for high affinity interactions with MHC class II molecules and thus SED was co-crystallized with Zn2+. The crystal structure of SED has been determined in two different space groups, at 2.3 and 3.0 A resolution respectively. The three-dimensional structure of SED is similar to structures of other bacterial superantigens, although this study has revealed that SED has the unique capability of forming dimers in the presence of Zn2+. The high affinity Zn2+ site used in dimer formation is located on the surface of the beta-sheet in the C-terminal domain. Two bound metal ions are coordinated by residues from both molecules in the dimer interface and thus contribute directly to formation of the dimer. A second Zn2+ site is located on the surface close to the domain interface of the molecule. The unique feature of SED in forming a Zn2+-dependent homodimer seems to facilitate novel and biologically relevant multimeric interactions with MHC class II molecules, as shown by the induction of cytokine mRNA in human monocytes when exposed to SED and SED mutants.

Interleukin-4, transforming growth factor beta 1, and dexamethasone inhibit superantigen-induced prostaglandin E2-dependent collagenase gene expression through their action on cyclooxygenase-2 and cytosolic phospholipase A2

Signalling via MHC class II in human fibroblast-like synoviocytes selectively induces interstitial collagenase gene expression over its natural inhibitor, the tissue inhibitor of metalloproteinase (TIMP), through a prostaglandin E2 (PGE2)-dependent pathway involving cyclooxygenase-2 (COX-2) and cytosolic phospholipase A2 (cPLA2). In the present study, we investigated the effect of three different agents the T-cell-derived cytokine IL-4, transforming growth factor beta 1 (TGF-beta 1), and dexamethasone (DXS) on this response. Our results indicate that treatment of superantigen-stimulated synoviocytes with DXS or IL-4 inhibited collagenase gene expression without affecting TIMP gene expression. In contrast, treatment of superantigen-stimulated synoviocytes with TGF-beta 1 resulted in an inhibition of collagenase induction and an increase in TIMP gene expression. IL-4, TGF-beta 1, and DXS abolished PGE2 production and the expression of COX-2 and cPLA2 but failed to affect the constitutive expression of COX-1 and secreted PLA2. Moreover, all agents abolished protein production and phosphorylation of COX-2 and cPLA2, respectively. The inhibitory effect of the three agents on collagenase gene expression was partially reversed by exogenous PGE2, which confirms that major histocompatibility complex class II-induced collagenase gene expression is regulated through a PGE2-mediated pathway. These data highlight a mode of action of a classical anti-inflammatory agent (DXS) and of two cytokines with recognized anti-inflammatory characters (IL-4 and TGF-beta 1) on a major histocompatibility complex class II-induced response and support the involvement of COX-2 and cPLA2 in major histocompatibility complex class II-induced interstitial collagenase production in human fibroblast-like synoviocytes.

Synergistic effect between CD40 and class II signals overcome the requirement for class II dimerization in superantigen-induced cytokine gene expression

Although staphylococcal enterotoxin A (SEA), B (SEB), and toxic shock syndrome toxin 1 (TSST-1) bind to major histocompatibility complex (MHC) class II molecules, they differ in their mode of binding. Signaling induced by these toxins via MHC class II molecules seems to be largely mediated by their mode of interaction. In the present study, we have demonstrated that contrary to SEA, stimulation of the human monocytic cell line THP-1 with SEB or TSST-1 failed to induce interleukin-1 beta or tumor necrosis factor-alpha gene expression. Treatment of THP-1 cells with interferon-gamma increased the level of MHC class II expression but did not enhance the SEB and TSST-1 response. However, cross-linking of SEB or TSST-1 bound to MHC class II molecules with specific antibodies leads to cytokine gene expression, indicating that dimerization of class II molecules is a requirement for this superantigen-induced response. The presence of anti-CD40 antibodies in the course of SEB or TSST-1 stimulation overcomes this requirement, indicating that certain signal(s) induced via CD40 molecules can replace those induced by dimerization of class II molecules. Pretreatment with anti-lymphocyte functional antigen-1 (LFA-1) antibodies completely inhibited SEA-induced response as well as that induced by SEB or TSST-1 in the presence of CD40 antibodies, supporting the involvement of LFA-1 intercellular adhesion molecule system in these responses. The entirety of these results demonstrate clearly that dimerization of class II molecules is a prerequisite for superantigen-induced T cell-independent cytokine gene expression which can be replaced by signaling via CD40 in an LFA-1-dependent system.

Cross-linking of major histocompatibility complex class II molecules by staphylococcal enterotoxin A superantigen is a requirement for inflammatory cytokine gene expression

Staphylococcal enterotoxin A (SEA) has two distinct binding sites for major histocompatibility complex (MHC) class II molecules. The aspartic acid located at position 227 (D227) in the COOH terminus of SEA is one of the three residues involved in its interaction with the DR beta chain, whereas the phenylalanine 47 (F47) of the NH2 terminus is critical for its binding to the DR alpha chain. Upon interaction with MHC class II molecules, SEA triggers several cellular events leading to cytokine gene expression. In the present study, we have demonstrated that, contrary to wild-type SEA, stimulation of the THP1 monocytic cell line with SEA mutated at position 47 (SEAF47A) or at position 227 (SEAD227A) failed to induce interleukin 1 beta and tumor necrosis factor-alpha messenger RNA expression. Pretreatment of the cells with a 10-fold excess of either SEAF47A or SEAD227A prevented the increase in cytokine messenger RNA induced by wild-type SEA. However, cross-linking of SEAF47A or SEAD227A bound to MHC class II molecules with F(ab')2 anti-SEA mAb leads to cytokine gene expression, whereas cross-linking with F(ab) fragments had no effect. Taken together, these results indicate that cross-linking of two MHC class II molecules by one single SEA molecule is a requirement for cytokine gene expression.

Superantigen-induced collagenase gene expression in human IFN-gamma-treated fibroblast-like synoviocytes involves prostaglandin E2. Evidence for a role of cyclooxygenase-2 and cytosolic phospholipase A2

MHC class II molecules expressed in lymphoid and nonlymphoid cells act as signal-transducer molecules. We demonstrate that engagement of MHC class II molecules on human IFN-gamma-treated fibroblast-like synoviocytes by their natural ligand, the staphylococcal enterotoxin A (SEA), selectively induces the production of interstitial collagenase over the expression of the tissue inhibitor of metalloproteinase (TIMP). Collagenase gene expression required de novo protein synthesis and was accompanied by high levels of PGE2 production, suggesting its implication in this response. Two inhibitors that affect prostaglandin biosynthesis, indomethacin and arachidonyl-trifluoromethyl-ketone, inhibited both PGE2 production and collagenase gene expression. The addition of exogenous PGE2 to inhibitor-treated cells partially restored the SEA-induced collagenase, indicating a role for PGE2 in this response. As cyclooxygenases (COX-1 and -2), cytosolic phospholipase A2 (cPLA2), and secreted PLA2 (sPLA2) are the enzymes potentially implicated in prostaglandin synthesis, their involvement in SEA-induced collagenase was investigated. The mRNA levels of COX-2 and cPLA2 rapidly increased following ligation of MHC class II molecules, while COX-1 and sPLA2 mRNA levels were unchanged and transiently depressed, respectively. SEA-induced COX-2 mRNA was translated adequately to protein, whereas cPLA2 protein level was not enhanced, but rapidly phosphorylated, a process previously linked to the enzyme activation. In conclusion, this work demonstrates a selective induction of collagenase gene expression over its natural inhibitor TIMP in human IFN-gamma-treated fibroblast-like synoviocytes mediated, at least in part, by PGE2, and provides evidence that signaling via MHC class II molecules induces the production of PGE2 through enhanced production of COX-2 and possibly activation of the cPLA2.

Superantigen-induced collagenase gene expression in human IFN-gamma-treated fibroblast-like synoviocytes involves prostaglandin E2. Evidence for a role of cyclooxygenase-2 and cytosolic phospholipase A2

MHC class II molecules expressed in lymphoid and nonlymphoid cells act as signal-transducer molecules. We demonstrate that engagement of MHC class II molecules on human IFN-gamma-treated fibroblast-like synoviocytes by their natural ligand, the staphylococcal enterotoxin A (SEA), selectively induces the production of interstitial collagenase over the expression of the tissue inhibitor of metalloproteinase (TIMP). Collagenase gene expression required de novo protein synthesis and was accompanied by high levels of PGE2 production, suggesting its implication in this response. Two inhibitors that affect prostaglandin biosynthesis, indomethacin and arachidonyl-trifluoromethyl-ketone, inhibited both PGE2 production and collagenase gene expression. The addition of exogenous PGE2 to inhibitor-treated cells partially restored the SEA-induced collagenase, indicating a role for PGE2 in this response. As cyclooxygenases (COX-1 and -2), cytosolic phospholipase A2 (cPLA2), and secreted PLA2 (sPLA2) are the enzymes potentially implicated in prostaglandin synthesis, their involvement in SEA-induced collagenase was investigated. The mRNA levels of COX-2 and cPLA2 rapidly increased following ligation of MHC class II molecules, while COX-1 and sPLA2 mRNA levels were unchanged and transiently depressed, respectively. SEA-induced COX-2 mRNA was translated adequately to protein, whereas cPLA2 protein level was not enhanced, but rapidly phosphorylated, a process previously linked to the enzyme activation. In conclusion, this work demonstrates a selective induction of collagenase gene expression over its natural inhibitor TIMP in human IFN-gamma-treated fibroblast-like synoviocytes mediated, at least in part, by PGE2, and provides evidence that signaling via MHC class II molecules induces the production of PGE2 through enhanced production of COX-2 and possibly activation of the cPLA2.

Superantigens initiate cognate CD4+ T cell/B cell interactions leading to early activation and proliferation of B cells

Dimerization or even multimerization of various receptors is commonly required for signal transduction. We report here that clustering of major histocompatibility complex class II molecules in human B cells by biotinylated staphylococcal enterotoxin A (SEA) cross-linked with avidin induces an increase in the level of intracellular calcium. This response was abolished by prior treatment with protein tyrosine kinase (PTK) inhibitors, suggesting that SEA-triggered calcium mobilization in B cells is probably dependent on the activation of PTK. The implication of PTK in SEA-induced early B cell activation was then confirmed by demonstrating that cross-linked SEA induces a significant increase in the level of tyrosine phosphorylation in B cells. The requirement of biotinavidin cross-linking in SEA-induced calcium mobilization in B cells can be fulfilled by the addition CD4+ T cells, suggesting a role for CD4 molecules. Using the murine CD4- T cell hybridoma 3DT, or its derivative I1B3 transfected with human CD4 that both express SEA-specific TCR, we confirmed the CD4 requirement for B cell calcium mobilization and that both specific TCR and CD4 molecules are required in early events of B cell activation induced by SEA. The role of CD4 in SEA-induced B cell proliferation was then investigated. SEA-stimulated B cells proliferated in the presence of CD4+ T cells, whereas no response was observed in the presence of CD8+ T cells. The addition of clone I1B3 CD4+ T cells failed to fulfill the requirement of CD4+ T cells in SEA-induced B cell proliferation, indicating the possible involvement of other CD4+ T cell surface molecules in this response. This issue is currently under investigation.

A natural mutation of the amino acid residue at position 60 destroys staphylococcal enterotoxin A murine T-cell mitogenicity

A variety of techniques have been used to identify the amino acid residues of bacterial superantigens involved in their interactions with major histocompatibility complex (MHC) class II and T-cell receptor (TCR). In this study, we isolated a naturally mutated staphylococcal enterotoxin A (SEA) from three different Staphylococcus aureus strains, in which the amino acid at position 60 has been changed from aspartic acid (D) to asparagine (N). We then studied the influence of this change on the immunological activities of SEA. Our results demonstrated that this mutation does not affect the capacity of SEA to bind MHC class II molecules and consequently activates human monocytes and peripheral blood lymphocytes. In contrast, mutated SEA failed to stimulate the proliferation of murine splenic lymphocytes of two different strains, and when presented by human MHC class II molecules, it also failed to activate murine cell line 3DT, which expresses the SEA-specific TCR V beta element (V beta 1). These results indicate that this mutation alters the interaction between SEA and murine TCR. The reactivity patterns of the mutated SEA with two specific anti-SEA monoclonal antibodies suggested that the observed effect of the isolated mutation in the murine system might be due to certain conformational changes in the SEA molecule introduced upon changing the D at position 60 to N. Site-directed mutagenesis of the N residue to D or to glycine reconstituted the ability of SEA to stimulate murine splenic lymphocytes. The different effects of this natural mutation at position 60 on the immunological activities of SEA with murine and human cells highlight the relevance of the affinity and avidity in SEA-TCR interactions in the function of different species or may reflect a difference in epitope specificity.

Induction of chemokine gene expression by major histocompatibility complex class II ligands in human fibroblast-like synoviocytes. Differential regulation by interleukin-4 and dexamethasone

Chemokines play a key role in recruiting leukocytes into inflamed synovial environment, and the cells of the synovial membrane, which express high levels of major histocompatibility complex (MHC) class II molecules, are a major source of these chemokines. Our data indicated that engagement of MHC class II molecules by staphylococcal enterotoxin A superantigen resulted in the induction of chemokine gene expression as well as protein synthesis. Pretreatment of the cells with cycloheximide potentiated the effect of superantigen on chemokine mRNA induction, suggesting that the expression of these genes may occur independently of prior protein synthesis. Ligation of MHC class II molecules in fibroblast-like synoviocytes by other ligands such as Mycoplasma arthritidis-derived superantigen and anti-class II antibody could also trigger an increase in the mRNA level of RANTES, MCP-1, and interleukin (IL)-8. The addition of dexamethasone to superantigen-treated fibroblast-like synoviocytes inhibited the mRNA expression of all three chemokines. IL-4 treatment decreased only the stimulating effect of superantigen on RANTES messanger suggesting that different mechanisms are involved in regulating these genes. The inhibitory effect of dexamethasone did not require a de novo protein synthesis, whereas that of IL-4 was protein-dependent. This report demonstrates that MHC class II ligands (superantigens and anti-MHC class II antibodies) may represent an important agent by which inflammatory chemokines can be induced and shows that this response can be modulated by the anti-inflammatory agents dexamethasone and IL-4.

Subsets of HLA-DR1 molecules defined by SEB and TSST-1 binding

Superantigens bind to major histocompatibility complex class II molecules on antigen-presenting cells and stimulate T cells. Staphylococcus aureus enterotoxin B (SEB) and toxic shock syndrome toxin-1 (TSST-1) bind to the same region of human lymphocyte antigen (HLA)-DR1 but do not compete with each other, which indicates that they bind to different subsets of DR1 molecules. Here, a mutation in the peptide-binding groove disrupted the SEB and TSST-1 binding sites, which suggests that peptides can influence the interaction with bacterial toxins. In support of this, the expression of the DR1 molecule in various cell types differentially affected the binding of these toxins.

T cell receptor-major histocompatibility complex class II interaction is required for the T cell response to bacterial superantigens

Bacterial and retroviral superantigens (SAGs) stimulate a high proportion of T cells expressing specific variable regions of the T cell receptor (TCR) beta chain. Although most alleles and isotypes bind SAGs, polymorphisms of major histocompatibility complex (MHC) class II molecules affect their presentation to T cells. This observation has raised the possibility that a TCR-MHC class II interaction can occur during this recognition process. To address the importance of such interactions during SAG presentation, we have used a panel of murine T cell hybridomas that respond to the bacterial SAG Staphylococcal enterotoxin B (SEB) and to the retroviral SAG Mtv-7 when presented by antigen-presenting cells (APCs) expressing HLA-DR1. Amino acid substitutions of the putative TCR contact residues 59, 64, 66, 77, and 81 on the DR1 beta chain showed that these amino acids are critical for recognition of the SAG SEB by T cells. TCR-MHC class II interactions are thus required for T cell recognition of SAG. Moreover, Mtv-7 SAG recognition by the same T cell hybridomas was not affected by these mutations, suggesting that the topology of the TCR-MHC class II-SAG trimolecular complex could be different from one TCR to another and from one SAG to another.

Modulation of Mycoplasma arthritidis-derived superantigen-induced cytokine gene expression by dexamethasone and interleukin-4

Activation of human monocytes or monocytic cell lines with all known stimuli coordinately induces the gene expression of various cytokines, including tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and the IL-1 receptor antagonist (IL-1Ra). In contrast, superantigens induce TNF-alpha and IL-1 beta but fail to affect IL-1Ra gene expression, suggesting that activation of monocytes via major histocompatibility complex class II is distinct from other signal transduction pathways. In the present study, we analyzed the regulation of the Mycoplasma arthritidis-derived superantigen (MAM)-induced IL-1 beta and TNF-alpha gene expression by studying the effects of two different anti-inflammatory agents: dexamethasone (DEX) and the T-cell-derived cytokine IL-4. Both agents contributed to the downregulation of MAM-induced IL-1 beta and TNF-alpha gene expression. They accelerated the normal decline of the gene expression of both MAM-induced cytokines by decreasing the stability of mRNAs via the induction or enhanced synthesis of one or more regulatory proteins. In addition, IL-4, but not DEX, induced a strong and rapid expression of IL-1Ra mRNA in MAM-stimulated and unstimulated THP-1 cells in a de novo protein synthesis-independent manner. The capacity of IL-4 to induce IL-1Ra gene expression reinforces its anti-inflammatory activity. This study illustrates some of the mechanisms by which MAM-induced proinflammatory monokine gene expression can be downregulated by IL-4 and DEX.

Signalling via MHC class II molecules selectively induces IL-1 beta over IL-1 receptor antagonist gene expression

Activation of human monocytes or human monocytic cell lines by several types of stimuli coordinately induces IL-1 beta and its antagonist (IL-1Ra) gene expression; alterations in their balance seem to mediate the inflammatory response. Using the human monocytic cell line THP-1, we report that superantigens, such as staphylococcal enterotoxin A (SEA) and Mycoplasma arthritidis -derived superantigen (MAM) induce an increase in the level of IL-1 beta mRNA without any detectable effect on IL-Ra mRNA. Unlike MAM-induced IL-1 beta mRNA, SEA-induced IL-1 beta mRNA was adequately translated into protein. Superantigen-induced gene expression is mediated by signalling, via their receptors, the MHC class II molecules. Thus, it appears that this mode of signalling selectively induces the proinflammatory cytokine IL-1 beta gene expression which, by itself, can have major importance in disease pathology especially in autoimmune diseases.

Mycoplasma arthritidis-derived superantigen induces proinflammatory monokine gene expression in the THP-1 human monocytic cell line

Soluble factors produced by Mycoplasma arthritidis play an important role in the pathology of arthritis in rodents, which closely resembles human rheumatoid arthritis. At least one of the products of these microorganisms, M. arthritidis-T cell mitogen (MAM), has biological activities in common with superantigens. These superantigens activate T cells in a V beta-restricted fashion, and this response is strictly dependent on the presence of major histocompatibility complex (MHC) class II-positive cells. In the present study, we have examined the ability of MAM to induce proinflammatory monokine (interleukin 1 beta [IL-1 beta] and tumor necrosis factor alpha [TNF-alpha]) gene expression in the THP-1 monocytic cell line. Treatment of these cells (which express a very low level of HLA-DR molecules) with gamma interferon (INF-gamma) induced HLA-DR, -DQ, and -DP molecules and enabled them to respond to MAM in a dose-dependent manner, resulting in an increase in the level of steady-state mRNA for IL-1 beta and TNF-alpha. Stimulation of the U937 monocytic cell line (MHC class II-negative even after INF-gamma treatment) with MAM did not induce either IL-1 beta or TNF-alpha transcription. Moreover, MAM adsorption on Raji (MHC class II-positive) cells resulted in the loss of its cytokine-inducing activity to induce monokine gene expression. These findings demonstrate clearly that MAM induces monokine gene expression following interaction with MHC class II molecules. Pretreatment of INF-gamma-treated THP-1 cells with the transcription inhibitor actinomycin D prevented the induction of monokine mRNA, whereas cycloheximide superinduced mRNA after stimulation with MAM. Finally, our results, obtained with protein tyrosine kinase inhibitors and antiphosphotyrosine Western blotting (immunoblotting), indicate that protein tyrosine kinase is involved in MAM-induced IL-1 beta and TNF-alpha gene expression in the THP-1 monocytic cell line. The capacity of MAM to induce proinflammatory cytokine transcription in monocytes via MHC class II molecules can be one pathway of MAM contribution to autoimmune diseases.

Changes in folate and pterin metabolism after disruption of the Leishmania H locus short chain dehydrogenase gene

The short chain dehydrogenase gene ltdh, which is derived from the H locus of Leishmania, confers high level resistance to the dihydrofolate reductase inhibitor methotrexate via a novel mechanism. Resistance is correlated with LTDH overproduction. High level resistance of ltdh transfectants was observed even in poor media where reduced folates are essential for the synthesis of thymidylate precursors. The ltdh transfectants were also capable of growing for several passages, at slightly reduced rates, in unsupplemented folate-deficient medium (fdDME-L), unlike the wild-type cells that could grow only in fdDME-L if supplemented with various folates or pterins. An homozygous ltdh mutant was obtained by gene targeting. This mutant became hypersensitive to methotrexate, but unlike wild-type cells, methotrexate toxicity could not be circumvented by the addition of thymidine. Although the homozygous mutant was capable of growing in fdDME-L supplemented with folate derivatives, it lost its ability to thrive in fdDME-L supplemented with pterins. Our results support the model in which LTDH is a key enzyme responsible for the conversion of a pterin derivative into an essential cofactor. This essential cofactor can also be converted into reduced folates at sufficient levels for growth when LTDH is overproduced, rendering dihydrofolate reductase dispensable. The novelty and uniqueness of LTDH opens the possibility of developing parasite-specific inhibitors.