A systematic review of conversion from calcineurin inhibitor to mammalian target of rapamycin inhibitors for maintenance immunosuppression in kidney transplant recipients.

This was a systematic review of randomized controlled trials comparing delayed conversion of mammalian target of rapamycin inhibitors (mTORi) for calcineurin inhibitors (CNIs) versus CNI continuation in kidney transplantation. Databases (2000-2012) and conference abstracts (2009-2012) were searched giving a total of 29 trials. Outcomes analyzed included GFR, graft loss, rejection and adverse events and were expressed as weighted mean differences (WMDs) or as risk ratios (RRs). Patients converted to mTORi up to 1 year posttransplant in intention-to-treat analysis had higher GFR compared with those remaining on CNI (WMD 0.28 mL/min/1.73 m(2) , 95% confidence interval [CI] 0.21-0.36; I(2) = 68%, p < 0.001). Stratifying trials by time posttransplant or type of mTORi did not change the overall heterogeneity. For on-treatment population, mTORi was associated with higher GFR (14.21 mL/min/1.73 m(2) , 10.34-18.08; I(2) = 0%, p = 0.970) 2-5 years posttransplant. The risk of rejection at 1 year was higher in mTORi trials (RR 1.72, 1.34-2.22; I(2) = 12%, p = 0.330). Discontinuation secondary to adverse events was more common in patients on mTORi, whereas the incidence of skin cancers and cytomegalovirus infection was lower in patients on mTORi. Conversion from CNI to mTORi is associated with short-term improvements in GFR in a number of studies but longer-term follow-up data of graft and patient survival are required.

Efficacy of sotrastaurin plus tacrolimus after de novo kidney transplantation: randomized, phase II trial results.

Sotrastaurin, a novel immunosuppressant, blocks early T cell activation through protein kinase C inhibition. Efficacy and safety of sotrastaurin with tacrolimus were assessed in a dose-ranging non-inferiority study in renal transplant recipients. A total of 298 patients were randomized 1:1:1:1 to receive sotrastaurin 100 (n = 77; discontinued in December 2011) or 200 mg (n = 73) b.i.d. plus standard tacrolimus (sTAC; 5-12 ng/mL), sotrastaurin 300 mg (n = 75) b.i.d. plus reduced tacrolimus (rTAC; 2-5 ng/mL) or enteric-coated mycophenolic acid (MPA) plus sTAC (n = 73); all patients received basiliximab and corticosteroids. Composite efficacy failure (treated biopsy-proven acute rejection ≥ grade IA, graft loss, death or loss to follow up) rates at Month 12 were 18.8%, 12.4%, 10.9% and 14.0% for the sotrastaurin 100, 200 and 300 mg, and MPA groups, respectively. The median estimated glomerular filtration rates were 55.7, 53.3, 64.9 and 59.2 mL/min, respectively. Mean heart rates were faster with higher sotrastaurin doses and discontinuations due to adverse events and gastrointestinal adverse events were more common. Fewer patients in the sotrastaurin groups experienced leukopenia than in the MPA group (1.3-5.5% vs. 16.5%). Sotrastaurin 200 and 300 mg had comparable efficacy to MPA in prevention of rejection with no significant difference in renal function between the groups.

Sotrastaurin in calcineurin inhibitor-free regimen using everolimus in de novo kidney transplant recipients.

Sotrastaurin, a novel selective protein-kinase-C inhibitor, inhibits early T cell activation via a calcineurin-independent pathway. Efficacy and safety of sotrastaurin in a calcineurin inhibitor-free regimen were evaluated in this two-stage Phase II study of de novo kidney transplant recipients. Stage 1 randomized 131 patients (2:1) to sotrastaurin 300 mg or cyclosporine A (CsA). Stage 2 randomized 180 patients (1:1:1) to sotrastaurin 300 or 200 mg or CsA. All patients received basiliximab, everolimus (EVR) and prednisone. Primary endpoint was composite efficacy failure rate of treated biopsy-proven acute rejection, graft loss, death or lost to follow-up. Main safety assessment was estimated glomerular filtration rate (eGFR) by MDRD-4 at Month 12. Composite efficacy failure rates at 12 months were higher in sotrastaurin arms (Stage 1: 16.5% and 10.9% for sotrastaurin 300 mg and CsA; Stage 2: 27.2%, 34.5% and 19.4% for sotrastaurin 200 mg, 300 mg and CsA). eGFR was significantly better in sotrastaurin groups versus CsA at most time points, except at 12 months. Gastrointestinal and cardiac adverse events were more frequent with sotrastaurin. Higher treatment discontinuation, deaths and graft losses occurred with sotrastaurin 300 mg. Sotrastaurin combined with EVR showed higher efficacy failure rates and some improvement in renal allograft function compared to a CsA-based therapy.

FTY720 versus MMF with cyclosporine in de novo renal transplantation: a 1-year, randomized controlled trial in Europe and Australasia.

FTY720 is a novel immunomodulator investigated in de novo renal transplantation and other therapeutic areas including multiple sclerosis. This 1-year multicenter, randomized, phase III study in 668 de novo renal transplant patients compared FTY720 2.5 mg plus full-dose cyclosporine (FDC) or FTY720 5.0 mg plus reduced-dose cyclosporine (RDC), with mycophenolate mofetil (MMF) plus FDC. The primary efficacy endpoint was the composite incidence of first treated biopsy-proven acute rejection (BPAR), graft loss, death or premature study discontinuation at month 12. Primary efficacy with FTY720 2.5 mg and MMF (32.4% and 30.2%; p = NS), plus mortality and BPAR incidence, were comparable. Patients receiving FTY720 5.0 mg plus RDC were discontinued from treatment due to increased risk of acute rejection (primary endpoint incidence 47.3%). FTY720 was associated with lower creatinine clearance (month 12: 53.1, 56.0 vs. 65.1 mL/min; p < 0.001) and more macular edema cases (2.2% and 1.3% vs. 0%), whereas cytomegalovirus infections were higher with MMF (6.2% and 10.6% vs. 18.1% p < 0.0001 and p = 0.0139, respectively). FTY720 2.5 mg provided comparable rejection prophylaxis over 12 months versus MMF; however, FTY720 5.0 mg did not support a 50% reduction in cyclosporine exposure. The cause of macular edema cases and lower creatinine clearance with FTY720 in de novo transplantation needs further investigation.

Interleukin-18 affects local cytokine expression but does not impact on the development of kidney allograft rejection.

Interleukin-18 is predominantly a macrophage-derived cytokine with a key role in inflammation and cell-mediated immunity. Having previously demonstrated IL-18 upregulation in a rat model of kidney rejection, here we examined IL-18 in a fully MHC-mismatched murine model of acute kidney rejection using IL-18-deficient recipients (IL-18-/-) and animals administered neutralizing IL-18 binding protein (IL-18BP). Gene expression of IL-18 and its receptor were significantly upregulated in allografts compared to isografts, as was the cellular infiltrate (T cells and macrophages) (p < 0.001). Allografts developed kidney dysfunction (p < 0.05) and tubulitis (p < 0.01) not observed in controls. There was a significant reduction in gene expression of IL-18 downstream pro-inflammatory molecules (iNOS, TNFalpha and IFNgamma) in IL-18-/- recipients (p < 0.01), and IL-18BP-treated animals. The CD4+ infiltrate and IL-4 mRNA expression was greater in the IL-18-/- recipients than wild-type (WT) allografts and IL-18BP-treated animals (p < 0.05), suggesting a Th2-bias which was supported by IFNgamma and IL-4 ELISPOT data and an increased eosinophil accumulation (p < 0.001). Neither IL-18 deficiency nor neutralization prevented renal dysfunction or tubulitis. This study demonstrates increased production of IL-18 in murine kidney allograft rejection and provides evidence that IL-18-induced pathways of inflammation are active. However, neither IL-18 deficiency nor neutralization was protective against the development of allograft rejection.

Graft function, cardiovascular risk factors, and sex hormones in renal transplant recipients on an immunosuppressive regimen of everolimus, reduced dose of cyclosporine, and basiliximab.

A prospective, randomized trial evaluated the combination of everolimus of 1.5 or 3 mg/d with steroids, basiliximab, and low-dose cyclosporine (CsA) adjusted by C2 monitoring in 256 renal transplant recipients. CsA C2 target levels, initially set at 600 ng/mL, were tapered over time posttransplant. The median serum creatinine concentrations were 130 mumol/L in both sirolimus groups (1.5 and 3 mg/d) at 6 months. Biopsy-proven acute rejection (BPAR) occurred in 13.7% and 15.1% of patients in the 1.5 and 3 mg/d groups, respectively. The incidence of BPAR was significantly higher among patients with everolimus trough levels < 3 ng/mL. Posttransplant diabetes mellitus occurred rarely, and blood pressure control appeared favorable; however, serum cholesterol levels were increased by approximately 50%, and serum triglycerides by approximately 100%. Serum testosterone concentrations increased after renal transplantation in both everolimus groups. Concentration-controlled everolimus therapy combined with low-dose CsA provides effective protection against rejection with good renal function and safety profiles.

Increased risk of hemorrhagic complications in renal allograft recipients receiving systemic heparin early posttransplantation.

UNLABELLED: The aim of this paper is to document the risk of hemorrhagic complications in renal allograft recipients requiring systemic heparinisation within the first 2 weeks posttransplantation. METHODS: A retrospective chart review of 326 RA recipients from January 1998 to July 2003 was subjected to statistics by SPIDA with P values <.05 considered significant. RESULTS: 16/326 (4.9%) recipients were initiated on intravenous (IV) heparin within the study period. Enoxaparin was subsequently used in 10/16 (62.5%) of these recipients. Intravenous heparin was instituted at a median 8 (1-14) days posttransplantation. Hemorrhagic complications occurred in 10/16 (62.5%) recipients on IV heparin versus 11/310 (3.5%) nonanticoagulated RA recipients (P = .0001). Hemorrhage occurred at a mean 9.75 (2-43) days into the course of IV heparin. The median peak APTT 24 hours prior to hemorrhage in RA recipients on heparin was 68.5 (58-180) versus a median peak APTT of 70 (50-140) among recipients on heparin who did not sustain a hemorrhagic complication (P = .30). A major intervention (predominantly surgery) was required in 6/16 (37%) recipients on IV heparin versus 7/310 (2.2%) nonheparinised RA recipients (P < .0001). Enoxaparin was instituted at a mean 22.5 (4-55) days posttransplantation. Delayed hemorrhage subsequently occurred in 4/10 (40%) recipients on enoxaparin. In conclusion, major and minor hemorrhagic complications occur more commonly among recipients requiring early post transplant IV heparin. Hemorrhage occurred despite APTT monitoring with APTT levels tending to be similar in RA recipients with versus without complications. Delayed hemorrhage was also seen with the subsequent use of enoxaparin.

Sirolimus-based therapy with or without cyclosporine: long-term follow-up in renal transplant patients.

This open-label, phase 3b, extension trial in renal transplant recipients (Sirolimus Study 311) assessed the long-term safety of sirolimus (SRL) administered with cyclosporine (CsA) (SRL + CsA group, n = 98) or without CsA (SRL group, n = 69). Renal transplant recipients who had either completed one of seven previous SRL studies sponsored by Wyeth Research or had participated for > or =3 months and reached a protocol-designated endpoint were eligible for enrollment. Data were available for 167 patients, all of whom initially received steroids. Mean total SRL exposure was 1526 days, including previous study participation. After enrollment in the extension study, there were significantly more acute rejections in the SRL + CsA group (6.1% vs 0%, P < .05). Differences in rates of graft loss (3.1% vs 1.4%) and death (6.1% vs 1.4%) were not significantly different between SRL + CsA and SRL groups, respectively. At 48 months after transplantation, calculated GFR (53.4 vs 70.9 mL/min) and hemoglobin (124.9 vs 136.6 g/L) were significantly better in the SRL group. Lipid values were not significantly different between groups at 48 months. The incidence of treatment-emergent increased creatinine, anemia, hypertension, headache, epistaxis, abnormal kidney function, and upper respiratory infection were significantly higher in the SRL + CsA group, whereas no adverse events were significantly higher in the SRL group. Malignancies were reported more frequently (11.2% vs 0%) with SRL + CsA. Results from this extension study indicate that SRL-based therapy without CsA is a safe alternative to combination therapy with CsA, offering long-term improvement in renal function with no increased risk of late acute rejection.

Reduced and standard target concentration tacrolimus with sirolimus in renal allograft recipients.

We report 6-month results of renal allograft recipients enrolled in seven Australian centers as part of a worldwide, multicenter, randomized, open-label, concentration-controlled trial comparing standard tacrolimus (sTAC) with reduced tacrolimus (rTAC) both with sirolimus (SRL) and steroids. Patients were randomized 1:1 to either rTAC (n = 33) with a target maintenance concentration of SRL of 8 to 15 ng/mL and TAC of 3 to 7 ng/mL, or sTAC (n = 31) with SRL target of 5 to 10 ng/mL and TAC of 8 to 12 ng/mL. Antibody induction was prohibited. Adult recipients of a first or second cadaveric or non-HLA-identical living donor renal graft were eligible for enrollment. Recipients with a panel-reactive antibody level of >50% and recipients of regrafts who had lost their first graft from rejection within the first 6 months were ineligible. The groups were compared for graft function, incidence of rejection, and patient and graft survival at 6 months. There were no differences in demographics. There were 30% and 29% discontinuations in the rTAC and sTAC groups mainly due to adverse events in the first month. The 6-month patient and graft survival by intention-to-treat analysis was 94% and 91% for rTAC and 100% and 97% for sTAC (P = NS), respectively. Incidence and severity of biopsy-proven acute rejection was not different between the two groups, being 21% for rTAC and 19% for sTAC. The mean serum creatinine was 121 micromol/L and 148 micromol/L for rTAC and sTAC groups (P =.09), respectively. Glomerular filtration rate (GFR) was 68 mL/min and 62 mL/min (P =.23), respectively. Adverse events, infections, and antihypertensive and antilipidemic agent usage were similar. Of interest is that the overall incidence of thrombotic microangiopathy was 14%. These results support the safety and efficacy of SRL + TAC. Reduced TAC is associated with a trend toward improved renal function.

Time course of upregulation of fibrogenic growth factors and cellular infiltration in a rodent model of chronic renal allograft rejection.

BACKGROUND: Chronic Rejection (CR) is the leading cause of renal allograft dysfunction. Upregulation of growth factors has been shown in CR but the time point at which this occurs in not known. The aim of this study was to examine the time course of upregulation of growth factors and correlate this with the macrophage and myofibroblast interstitial infiltrate. METHODS: Using a rat model of CR (F344 kidney donor to Lewis recipient), infiltration by ED1 + macrophages and proliferation of alpha-smooth muscle actin (alpha-SMA) and desmin-expressing cells was examined using immunohistochemistry. In addition, expression of mRNA for interferon-gamma (IFN-gamma), transforming growth factor-beta (TGF-beta), basic-fibroblast growth factor (b-FGF) and vascular endothelial growth factor (VEGF) was studied using a semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique. Native Lewis rat kidney and Lewis-Lewis isografts were used as controls. RESULTS: Immunohistochemical staining of ED1 + cells showed a marked increase in the macrophage infiltrate of allografts compared to isografts at all time periods (P = 0.0002) peaking at weeks 8-12 after transplantation. Expression of alpha-SMA was also increased in allografts (P = 0.002). RT-PCR analysis showed that mRNA for TGF-beta was maximally upregulated in allografts in comparison to isografts at week 8 after engraftment (P = 0.05) and declined thereafter, although remained at elevated levels compared to controls. IFN-gamma and b-FGF gene expression was increased in allografts late in the post-transplantation period. CONCLUSION: Early infiltration of macrophages and production of TGF-beta1 was followed by later upregulation of fibrogenic growth factors and myofibroblasts associated with interstitial fibrosis and organ dysfunction.

Sirolimus allows early cyclosporine withdrawal in renal transplantation resulting in improved renal function and lower blood pressure.

INTRODUCTION: This study evaluated whether cyclosporine (CsA) could be eliminated from a sirolimus (Rapamune, rapamycin, SRL)-CsA-steroid (ST) regimen at 3 months. METHODS: This was an open-label study conducted in Europe, Australia, and Canada. Upon enrollment, 525 primary (90%) or secondary (10%) renal allograft recipients with cadaveric (89%) or living (11%) donors received 2 mg of sirolimus (troughs>5 ng/ml), CsA, and steroids. At 3 months+/-2 weeks, eligible patients were randomized (1:1) to remain on SRL-CsA-ST or to have CsA withdrawn and therapy continued with SRL (troughs 20-30 ng/ml)-ST. RESULTS: At 12 months, overall graft and patient survival were 89.1% and 94.9%, respectively. In the 430 (82%) randomized patients, there was no difference in graft survival (95.8% vs. 97.2%, SRL-CsA-ST vs. SRL-ST) or patient survival (97.2% vs. 98.1%, respectively). The incidence of biopsy-confirmed primary acute rejection was 13.1% during the prerandomization period. After randomization, the acute rejection rates were 4.2% and 9.8% for SRL-CsA-ST and SRL-ST, respectively (P=0.035). Renal function (calculated glomerular filtration rate, 57 vs. 63 ml/min, P<0.001) and blood pressure significantly improved when CsA was withdrawn. Hypertension, CsA nephrotoxicity, hyperuricemia, and Herpes zoster occurred statistically more frequently in patients remaining on CsA, whereas thrombocytopenia, abnormal liver function tests, and hypokalemia were reported more often for SRL-ST therapy. CONCLUSION: Sirolimus, CsA, and steroids for 3 months posttransplant, followed by elimination of CsA, is a safe and effective alternative to continuous therapy with sirolimus, CsA, and steroids that can result in better renal function and lower blood pressure.

Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) for measurement of cytokine and growth factor mRNA expression with fluorogenic probes or SYBR Green I.

Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) is the method of choice for rapid and reproducible measurements of cytokine or growth factor expression in small samples. Fluorescence detection methods for monitoring real-time PCR include fluorogenic probes labelled with reporter and quencher dyes, such as Taqman probes or Molecular Beacons and the dsDNA-binding dye SYBR Green I. Fluorogenic (Taqman) probes for a range of human and rat cytokines and growth factors were tested for sensitivity and compared with an assay for SYBR Green I quantification using real-time fluorescence monitoring (PE Applied Biosystems Model 7700 sequence detector). SYBR Green I detection involved analysis of the melting temperature of the PCR product and measurement of fluorescence at the optimum temperature. Fluorogenic probes provided sensitive and reproducible detection of targets that ranged from low (<10 copies/reaction) to high (>107 copies/ reaction) expression. SYBR Green I gave reproducible quantification when the target gene was expressed at moderate to high levels (> or =1000 copies/reaction), but did not give consistently reproducible quantification when the target gene was expressed at low levels. Although optimization of melting temperature improved the specificity of SYBR Green I detection, in our hands it did not equal the reproducible sensitivity and specificity of fluorogenic probes. The latter method is the first choice for measurement of low-level gene expression, although SYBR Green I is a simple and reproducible means to quantify genes that are expressed at moderate to high levels.

Frequency of cytochrome P450 3A4 variant genotype in transplant population and lack of association with cyclosporin clearance.

OBJECTIVE: Cytochrome P450 3A4 (CYP3A4) plays a vital role in the oxidative metabolism of many xenobiotics. Some recent reports have provided circumstantial evidence in support of an association between a genetic polymorphism (A-->G) in the 5'-flanking region (-290) of CYP3A4 and altered enzyme activity. We sought to determine whether genotyping patients for CYP3A4-G could assist with the dose optimisation of drugs metabolised by this system. METHODS: Normal subjects and renal-transplant patients receiving cyclosporin for immune modulation were genotyped for the CYP3A4-G variant. A surrogate for cyclosporin clearance was estimated from the ratio of the cyclosporin dose, normalised for body weight and the corresponding trough concentration. The association between genotype and clearance was examined in patients who received twice-daily doses of cyclosporin and who were not on concurrent medication known to modify CYP3A4 function. RESULTS: The allelic frequencies of the CYP3A4-G variant were estimated to be 2.6% and 3% in transplant patients and normal subjects, respectively. The median cyclosporin pseudo-clearance of transplant patients with wild-type CYP3A4 was 0.90 l/h/kg (range: 0.35-3.8 l/h/kg; n = 86), whereas the corresponding value for the five patients heterozygotic for the CYP3A4-G variant was 0.71 l/h/kg (range 0.35-0.91 l/h/kg). The distribution of the pseudo-clearance according to genotype was not found to be significant according to a Fisher's exact test (P = 0.15). CONCLUSION: Genotyping for the CYP3A4-G polymorphism is unlikely to assist cyclosporin dose selection in transplant patients.

Early up-regulation of macrophages and myofibroblasts: a new marker for development of chronic renal allograft rejection.

BACKGROUND: Increased numbers of macrophages and myofibroblasts are observed to occur in chronic renal allograft rejection (CR). The aim of this study was to examine the expression of cellular markers for the macrophage and myofibroblast in early renal transplant biopsy specimens and correlate these findings with allograft outcome. METHODS: The first postengraftment biopsy specimens from 53 patients who underwent renal transplantation between January 1993 and December 1995 were studied using immunohistochemistry with antibodies to alpha-smooth muscle actin, which identifies myofibroblasts and CD68, a marker for monocytes and macrophages. Patients were followed until December 1998 (mean follow-up 4.7+/-1.2 years). RESULTS: Nine patients had progressed to CR by the time of the study, whereas 44 patients continued to have stable renal function. A marked increase in both macrophages (P=0.02) and myofibroblasts (P=0.04) was noted in the first biopsy specimen obtained after engraftment in the patients who developed CR compared with those with stable allograft function. There was a positive correlation between alpha-smooth muscle actin and collagen expression (P=0.0001). CONCLUSION: Significant increases in macrophages and myofibroblasts occur in the first renal biopsy specimen in those patients who later develop CR.

Vascular endothelial growth factor expression in human chronic renal allograft rejection.

BACKGROUND: Chronic renal allograft rejection is characterized by interstitial fibrosis and vasculopathy. Vascular endothelial growth factor (VEGF) is an endothelial mitogen with increased expression in inflammation and vasculopathy. METHODS: Renal tissue from 17 patients with chronic rejection was examined for VEGF protein and the presence of CD 68-positive macrophages, and compared to biopsies from patients with temporary allograft dysfunction, acute rejection, and native kidneys with thin membrane disease. RESULTS: In the chronic rejection group, there was markedly increased expression of VEGF protein in the interstitium (P<0.0001). In serial sections, VEGF colocalized with the expression of CD 68-positive macrophages. Significantly more macrophages were in the tubulointerstitium in tissue with chronic rejection than in those with temporary allograft dysfunction (P<0.005). Additionally, VEGF protein expression in the glomeruli and the vascular compartment of patients with chronic rejection was increased. CONCLUSION: The up-regulation of VEGF in chronic renal allograft rejection may be important in inflammation and development of fibrosis.

Anergic self-reactive B cells present self antigen and respond normally to CD40-dependent T-cell signals but are defective in antigen-receptor-mediated functions.

B-cell tolerance to soluble protein self antigens such as hen egg lysozyme (HEL) is mediated by clonal anergy. Anergic B cells fail to mount antibody responses even in the presence of carrier-primed T cells, suggesting an inability to activate or respond to T helper cells. To investigate the nature of this defect, B cells from tolerant HEL/anti-HEL double-transgenic mice were incubated with a membrane preparation from activated T-cell clones expressing the CD40 ligand. These membranes, together with interleukin 4 and 5 deliver the downstream antigen-independent CD40-dependent B-cell-activating signals required for productive T-B collaboration. Anergic B cells responded to this stimulus by proliferating and secreting antibody at levels comparable to or better than control B cells. Furthermore, anergic B cells presented HEL acquired in vivo and could present the unrelated antigen, conalbumin, targeted for processing via surface IgD. In contrast, the low immunoglobulin receptor levels on anergic B cells were associated with reduced de novo presentation of HEL and a failure to upregulate costimulatory ligands for CD28. These defects in immunoglobulin-receptor-mediated functions could be overcome in vivo, suggesting a number of mechanisms for induction of autoantibody responses.

Immunoglobulin M and D antigen receptors are both capable of mediating B lymphocyte activation, deletion, or anergy after interaction with specific antigen.

A series of immunoglobulin (Ig)-transgenic mice were generated to study the functional capabilities of the IgM and IgD classes of B lymphocyte antigen receptor in regulating both cellular development and responses to specific antigen. B cells from Ig-transgenic mice expressing either hen-egg lysozyme (HEL)-specific IgM or IgD alone were compared with B cells from mice that coexpressed IgM and IgD of the same anti-HEL specificity. In all three types of Ig-transgenic mice, conventional B cells specific for HEL exhibited exclusion of endogenous Ig expression and matured to populate the usual microenvironments in peripheral lymphoid tissues. These peripheral B cells could be stimulated by HEL through either IgM or IgD antigen receptors to generate T cell dependent antibody production in vivo or to enhance T cell independent proliferative responses to lipopolysaccharide in vitro. Conversely, when HEL was encountered in vivo as a self-antigen, B cells expressing HEL-specific IgM or IgD alone were both rendered tolerant. In each case this occurred by clonal anergy in response to soluble autologous HEL, and clonal deletion when HEL was recognized as a membrane-bound self-antigen. Taken together, these findings indicate that IgM and IgD antigen receptors expressed alone on conventional B cells can support normal differentiation, antigen-dependent activation, and induction of self-tolerance, the only overt difference lying in a greater degree of receptor downregulation for IgM relative to IgD after induction of clonal anergy by soluble HEL.