Knockout of the neonatal Fc receptor alters immune complex trafficking and lysosomal function in cultured podocytes

Podocytes are key to preventing the filtration of serum proteins into the urine. Recent evidence also suggests that in immune mediated kidney diseases, podocytes are the targets of immune complexes (ICs). The mechanisms whereby podocytes handle and respond to ICs remain unknown. The neonatal Fc receptor (FcRn) is involved in IgG handling in podocytes and is also required in dendritic cells to traffic ICs to the lysosome for proteolytic degradation of antigen and presentation on MHC II. Here we examine the role of FcRn in handling ICs in podocytes. We show that knockout of FcRn in podocytes results in decreased trafficking of ICs to the lysosome and increases IC trafficking to recycling endosomes. FcRn KO also alters lysosomal distribution, decreases lysosomal surface area and decreases cathepsin B expression and activity. We demonstrate that signaling pathways in cultured podocytes differ after treatment with IgG alone versus ICs and that podocyte proliferation in both WT and KO podocytes is suppressed by IC treatment. Our findings suggest that podocytes respond differentially to IgG versus ICs and that FcRn modifies the lysosomal response to ICs. Elucidating the mechanisms underlying podocyte handling of ICs may provide novel pathways to modulate immune mediated kidney disease progression.

Regulation of the Actin Cytoskeleton in Podocytes

Podocytes are an integral part of the glomerular filtration barrier, a structure that prevents filtration of large proteins and macromolecules into the urine. Podocyte function is dependent on actin cytoskeleton regulation within the foot processes, structures that link podocytes to the glomerular basement membrane. Actin cytoskeleton dynamics in podocyte foot processes are complex and regulated by multiple proteins and other factors. There are two key signal integration and structural hubs within foot processes that regulate the actin cytoskeleton: the slit diaphragm and focal adhesions. Both modulate actin filament extension as well as foot process mobility. No matter what the initial cause, the final common pathway of podocyte damage is dysregulation of the actin cytoskeleton leading to foot process retraction and proteinuria. Disruption of the actin cytoskeleton can be due to acquired causes or to genetic mutations in key actin regulatory and signaling proteins. Here, we describe the major structural and signaling components that regulate the actin cytoskeleton in podocytes as well as acquired and genetic causes of actin dysregulation.

An in vitro model of antibody-mediated injury to glomerular endothelial cells: Upregulation of MHC class II and adhesion molecules

Chronic active antibody-mediated rejection is a major cause of allograft failure in kidney transplantation. Microvascular inflammation and transplant glomerulopathy are defining pathologic features of chronic active antibody-mediated rejection and are associated with allograft failure. However, the mechanisms of leukocyte infiltration and glomerular endothelial cell injury remain unclear. We hypothesized MHC class II ligation on glomerular endothelial cells (GEnC) would result in upregulation of adhesion molecules and production of chemoattractants. A model of endothelial cell activation in the presence of antibodies to MHC classes I and II was used to determine the expression of adhesion molecules and chemokines. Murine GEnC were activated with IFNγ, which upregulated gene expression of β2-microglobulin (MHC class I), ICAM1, VCAM1, CCL2, CCL5, and IL-6. IFNγ stimulation of GEnC increased surface expression of MHC class I, MHC class II, ICAM1, and VCAM1. Incubation with antibodies directed at MHC class I or class II did not further enhance adhesion molecule expression. Multispectral imaging flow cytometry and confocal microscopy demonstrated MHC molecules co-localized with the adhesion molecules ICAM1 and VCAM1 on the GEnC surface. GEnC secretion of chemoattractants, CCL2 and CCL5, was increased by IFNγ stimulation. CCL2 production was further enhanced by incubation with sensitized plasma. Endothelial activation induces de novo expression of MHC class II molecules and increases surface expression of MHC class I, ICAM1 and VCAM1, which are all co-localized together. Maintaining the integrity and functionality of the glomerular endothelium is necessary to ensure survival of the allograft. IFNγ stimulation of GEnC propagates an inflammatory response with production of chemokines and co-localization of MHC and adhesion molecules on the GEnC surface, contributing to endothelial cell function as antigen presenting cells and an active player in allograft injury.

Knockout of the neonatal Fc receptor in cultured podocytes alters IL-6 signaling and the actin cytoskeleton

The neonatal Fc receptor (FcRn) has been shown to be required for antigen presentation in dendritic cells, and global knockout of FcRn attenuates immune-mediated kidney disease. Podocytes express interleukin-6 (IL-6) receptor and produce IL-6 under proinflammatory conditions. Here we examined the role of FcRn in the IL-6-mediated inflammatory response in podocytes. We examined IL-6 production by ELISA and expression by qPCR in wild type (WT) and FcRn knockout (KO) podocytes after treatment with proinflammatory stimuli as well as IL-6-mediated signaling via the JAK/STAT pathway. We also examined podocyte motility in cultured WT and KO podocytes after a proinflammatory challenge. We found that FcRn KO podocytes produced minimal amount of IL-6 after treatment with albumin, IgG, or immune complexes whereas WT podocytes had a robust response. FcRn KO podocytes also had minimal expression of IL-6 compared with WT. By Western blotting, there was significantly less phosphorylated STAT3 in KO podocytes after treatment with IFNγ or immune complexes. In a scratch assay, FcRn KO podocytes showed increased motility comparted KO, suggesting a defect in actin dynamics. Cultured FcRn KO podocytes also demonstrated abnormal stress fibers compared with WT and the defect could be rescued by IL-6 treatment. This study shows that in podocytes, FcRn modulates the IL-6 mediated response to proinflammatory stimuli and regulates podocytes actin structure, motility and synaptopodin expression.

Continuous Renal Replacement Therapy Dosing in the Severely Underweight: A Case Report

Guidelines recommend that patients treated with continuous renal replacement therapy be delivered an effluent dose of 20 to 25 mL/kg/h. There is debate, especially at the extremes of body mass index, as to whether actual or ideal body weight (IBW) should be used in these dose calculations. A middle-aged woman with severe anorexia presented with 48 hours of altered mental status. Laboratory tests showed severe metabolic acidosis necessitating intubation, which was ultimately found to be due to nonprescribed use of metformin for weight loss. The patient became anuric and was initiated on continuous venovenous hemodialysis. Due to refractory acidosis, the modality was converted to continuous venovenous hemodiafiltration by adding postfilter hypertonic bicarbonate solution. Based on changes in sodium and bicarbonate levels over 4 hours with hypertonic bicarbonate solution, we were able to calculate an “effective” volume of distribution for this severely underweight patient. Our calculations suggest that IBW gives a better approximation of effective volume of distribution than actual body weight in a severely underweight woman. Inadequate effluent flow rate calculated based on actual rather than IBW may lead to insufficient correction of metabolic derangements in extremely underweight patients.

Risk of adverse maternal and fetal outcomes during pregnancy in living kidney donors: A matched cohort study

BACKGROUND

We examined the risk of adverse pregnancy outcomes in primiparous kidney donors compared to matched controls.

METHODS

Fifty-nine women with a history of kidney donation prior to their first pregnancy with normal renal function and no history of kidney disease, diabetes or chronic hypertension were matched 1:4 by age (within 2 years) and race to women with two kidneys using data from an integrated healthcare delivery system. Adverse pregnancy outcomes were defined as preterm delivery (delivery <37 weeks), delivery via cesarean section, gestational hypertension, preeclampsia/eclampsia, gestational diabetes, length of stay in the hospital >3 days, infant death/transfer to acute facility and low birthweight (<2500 g).

RESULTS

Living kidney donors did not have a higher risk of adverse outcomes compared to matched controls. There was a trend toward an increased risk of preeclampsia/eclampsia in kidney donors but it did not reach statistical significance (Odds ratio [OR]: 2.96, 95% CI: 0.98-8.94, P = 0.06). However, in kidney donors ≤30 years of age, there was a fourfold increased risk of preeclampsia/eclampsia (OR: 4.09, 95% CI: 1.07-15.59, P = 0.04).

CONCLUSION

Overall, the risk of pregnancy-associated complications following kidney donation is small but potential female kidney donors should be counseled on the possible increased risk of preeclampsia.

Bacteremic pneumococcal pneumonia associated with macrolide failure

Despite rising rates of macrolide resistance to Streptococcus pneumoniae, the current guidelines for outpatient treatment of community-acquired pneumonia include a macrolide as initial empiric therapy. There have only been a few previously documented cases of macrolide treatment failure in community-acquired pneumonia and there is controversy as to whether macrolide resistance in S. pneumoniae is clinically important. Reported here are two cases of community-acquired pneumonia caused by S. pneumoniae, one of which was fatal, that failed to respond to clarithromycin.

Muscarinic receptor stimulation with edrophonium hydrochloride does not elevate ventricular fibrillation thresholds in humans

INTRODUCTION

Although decreased vagal tone, as measured by heart rate variability is a risk factor for ventricular fibrillation (VF) and sudden cardiac death, it is unknown whether increasing vagal tone has an antiarrhythmic effect. The purpose of this study was to determine whether edrophonium hydrochloride (HCI), a vagomimetic agent, increases VF threshold.

METHODS AND RESULTS

Twenty-eight consecutive patients with previously implanted defibrillators had two inductions of VF by monophasic direct-current shocks delivered at 10 to 30 msec after the T wave peak, escalating energies (0.4, 1, then 3 J) until VF was induced. If VF was not induced, this protocol was repeated at the T wave peak and then at 10 to 30 msec before the T wave until VF was induced. Patients were randomized to receive edrophonium HCl (12 to 18 mg) or no drug before repeating the protocol for the second VF induction. The mean sinus cycle length increased from 782 to 872 msec in the group receiving edrophonium HCI (P = 0.006 ). In the control group, the mean sinus cycle length remained unchanged (838 vs 858 msec). The mean energy to induce VF, coupling interval relative to the T wave, and the number of attempts to induce VF were not different between VF induction attempts 1 and 2, and they were not different between the group receiving edrophonium HCl and the control group.

CONCLUSION

In a sedated patient population with implantable defibrillators, edrophonium HCI infusion prolongs sinus cycle length but does not change inducibility of VF using T wave shocks.

Cycling of inducibility of paroxysmal supraventricular tachycardia in women and its implications for timing of electrophysiologic procedures

Arrhythmias in women may be affected by phases of the menstrual cycle. This study was designed to determine the prevalence of perimenstrual clustering of spontaneous episodes of paroxysmal supraventricular tachycardia (SVT) in women. It also tested the hypothesis that women with this temporal pattern of events have an altered probability of induction of paroxysmal SVT during electrophysiologic testing at higher estrogen states (midcycle or with estrogen replacement therapy) than at low estrogen states (perimenstrual or without estrogen replacement). A structured history of the relation of spontaneous paroxysmal SVTs to phases of the menstrual cycle was obtained prospectively among 42 women referred during a 3-year period. Patients with cyclical patterns of spontaneous tachycardias, who had had negative electrophysiologic studies at midcycle or while receiving estrogen replacement therapy, had repeat procedures (1) when premenstrual or at the onset of menses, or (2) after stopping estrogen replacement therapy. Seventeen of 42 consecutive female patients (40%) had histories of perimenstrual clustering of arrhythmias. Six women (4 with normal menstrual cycles, 2 on estrogen replacement therapy), who qualified for paired electrophysiologic studies because of a negative initial electrophysiologic study that included provocation with isoproterenol, had inducibility into SVTs during the second study. All 6 had dual atrioventricular (AV) nodal pathway physiology, 4 had AV nodal reentrant tachycardia (AVNRT) induced, 1 had both AVNRT and reciprocating AV tachycardias, and 1 had nonsustained AVNRT and an atrial tachycardia induced. Successful ablation procedures were performed in 5 of the 6 patients. Thus, among women with a history of perimenstrual clustering of paroxysmal SVT and among those receiving estrogen replacement therapy, scheduling of elective electrophysiologic procedures at times of low estrogen levels (premenstrual or off estrogen replacement therapy) may facilitate the probability of a successful procedure.

Comparison of spiramycin and doxycycline for treatment of Chlamydia trachomatis genital infections

We performed a single blind controlled multicenter study in which we compared the efficacy and safety of 100 mg of doxycycline versus those of 1 g (3 x 10(6) IU) of spiramycin given orally twice daily for 14 days in the treatment of culture-positive Chlamydia trachomatis genitourinary tract infections. A total of 367 patients were enrolled in the study, and 364 patients were evaluable for safety and 265 patients were evaluable for efficacy. The cure rate between treatment groups was not statistically significant, being 98% (125 of 128 patients) in the spiramycin group and 100% (133 of 133 patients) in the doxycycline group. Female patients who received spiramycin were more likely to report dysethesias that resolved after the completion of therapy. The results of the study show that spiramycin is an effective drug for the treatment of C. trachomatis infection and warrants further assessment over a shorter treatment period (7 days) and during pregnancy.

An unusual cause of cervical lymphadenitis: Kikuchi-Fujimoto disease

Cervical lymphadenitis may be the result of diverse conditions in a patient. Clinical and epidemiologic information about cervical lymphadenitis can often lead to a presumptive diagnosis and, thus, limit the number of studies required as well as direct the type of initial therapy administered. We report a case of cervical lymphadenitis in a Vietnamese woman for whom a presumptive diagnosis of tuberculosis was made and antituberculous therapy was started. Pathologic examination of an excised lymph node revealed the correct diagnosis--histiocytic necrotizing lymphadenitis, or Kikuchi-Fujimoto disease. We review the clinical, epidemiologic, and pathologic features of this recently recognized disease. Careful examination of excised material from the lymph nodes should prevent patients who have Kikuchi-Fujimoto disease from receiving unnecessary treatment.

Postpartum uterine infection with Clostridium perfringens

Clostridium perfringens is commonly present in the female genital tract. Uterine infection with this organism is a potentially fatal disease infrequently seen in obstetric practice. The manifestations of C. perfringens uterine infection are variable, ranging from endometritis to gas gangrene with fulminant septicemia. The usual precipitating event has been septic abortion, but such infections can also occur spontaneously in uterine tumors and after complicated deliveries requiring mechanical intervention. Diagnosis may be aided by radiologic techniques, and treatment involves high-dose penicillin and possibly surgery. We report two cases and review the clinical presentation and the diagnostic and therapeutic aspects of this disease.

Oral "hairy" leukoplakia: a clue to HIV-I exposure

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Single-dose ceftriaxone for chancroid

Men with genital ulcers that were culture positive for Haemophilus ducreyi were treated with intramuscular ceftriaxone and randomized to three different dose regimens. All but 1 of 50 men treated with 1 g of intramuscular ceftriaxone were cured. Similarly, 0.5 and 0.25 g cured 43 of 44 men and 37 of 38 men, respectively. A single dose of 250 mg of intramuscular ceftriaxone is an effective treatment for chancroid.

Single-dose therapy with trimethoprim-sulfametrole for chancroid in females

Women with genital ulcer disease who were culture-positive for Haemophilus ducreyi were treated with a single dose of the drug combination trimethoprim-sulfametrole; the dosage was 640 mg of trimethoprim and 3,200 mg of sulfametrole. All 27 women who were treated with this regimen and adequately followed were cured. Thus a single dose of trimethoprim-sulfametrole appears to be an effective treatment regimen for women with chancroid in Kenya.

Advances in the diagnosis and management of chancroid

Improved technologies for the cultural diagnosis of chancroid have resulted in increased interest in the management and control of genital ulcer disease. New treatment regimens have been identified, and new control strategies have evolved. These strategies now permit localized introductions of chancroid into developed countries to be contained rapidly. However, additional work is still necessary in developing countries.

Laboratory diagnosis of Haemophilus ducreyi: sensitivity of culture media

Laboratory confirmation of the clinical diagnosis of chancroid requires the isolation of Haemophilus ducreyi. Enriched gonococcal (GcHbS) and Mueller-Hinton agar (MHHb) both support the growth of most strains of H. ducreyi. In this study we compared the isolation rate of H. ducreyi on GcHbs and MHHb media in 111 men with genital ulcer disease. A second culture was obtained in 84 men at 48 hr in order to determine the reproducibility of H. ducreyi culture. The sensitivity of a single and a sequential pair of cultures on GcHbS was 67% and 74%, respectively, on men with presumed chancroid. The sensitivity of the MHHb as a single culture was 53%. Using both media for the initial culture of genital ulcers, and repeating the culture on GcHbs at 48 hr, increased the sensitivity of the isolation of H. ducreyi to 92% in men who had no prior antimicrobial use and who had no laboratory evidence of primary syphilis.

Cytomegalovirus infection and abnormal T-lymphocyte subset ratios in homosexual men

T-helper:T-suppressor cell ratios of 1 or less were found in 2 of 42 homosexual men without antibodies to cytomegalovirus but in 33 of 67 homosexual men with antibodies (p less than 0.001). Of 34 men without antibody who were followed prospectively, 12 became seropositive for cytomegalovirus and all 12 developed helper: suppressor ratios of less than 1.0. These ratios remained at 1 or less for an average of 9.6 months but persisted for 15 months or more in 3 men. None of the men in the prospective study developed antibodies to the acquired-immunodeficiency-syndrome-associated retrovirus. These results indicate that in the homosexual men studied, abnormally low T-lymphocyte helper: suppressor ratios occurred almost exclusively in those who were infected with cytomegalovirus, and in those prospectively followed low ratios did not reflect contact with the syndrome-associated retrovirus. Abnormal ratios were rarely seen in men who had never been exposed to cytomegalovirus. Thus, cytomegalovirus infection may be an important cofactor in the immunologic disorders leading to the acquired immunodeficiency syndrome.

Trimethoprim sulphamoxole in the treatment of chancroid. Comparison of two single dose treatment regimens with a five day regimen

In a prospective blinded study, 135 men with genital ulcers culture positive for Haemophilus ducreyi, were randomized to one of three regimens. Two single dose regimens, either the combination of sulphamoxole 3200 mg/trimethoprim 640 mg or trimethoprim 700 mg alone were compared to a five day regimen of sulphamoxole 800 mg/trimethoprim 160 mg twice daily. All 31 treated with a five day regimen of trimethoprim sulphamoxole healed without further treatment. Of 27 patients treated with the single dose sulphamoxole/trimethoprim regimen, only 21 were cured and of 34 treated with trimethoprim alone, 25 responded. Antibacterial susceptibilities were performed on 31 H. ducreyi isolates. The laboratory susceptibility of these strains to trimethoprim correlated with the clinical response to the single agent. Trimethoprim alone in a dose of 700 mg or the combination of sulphamoxole (3200 mg) and trimethoprim (640 mg) is not satisfactory for the single dose treatment of genital ulcer disease. However, when prescribed for five days, sulphamoxole/trimethoprim is effective and compares favourably with other treatment regimens.

Comparison of media for the primary isolation of Haemophilus ducreyi

The rates of isolation of Haemophilus ducreyi from patients with presumed chancroid has been low, and improved cultural techniques are required. We determined the isolation rates of H. ducreyi from 38 patients with clinical chancroid and compared gonococcal agar supplemented with bovine hemoglobin to Mueller-Hinton agar supplemented with chocolated horse blood, each with and without 5% fetal calf serum. The rate of isolation and the qualitative and quantitative growth of strains was best on gonococcal agar with added fetal calf serum (GC-HgS). However, three strains were isolated only on Mueller-Hinton base (MH-base). GC-HgS was compared with MH-HB for the isolation of H. ducreyi from 201 patients with clinical chancroid. Seventy-one percent of cultures were positive on GC-HgS, and 61% were positive on MH-HB (P less than .005); however, 10% of cultures were positive only on MH-HB. The use of the two media together increased the yield of positive cultures to 81%. Thus maximal rates of isolation of H. ducreyi from clinical specimens requires the use of two media, GC-HgS and MH-HB.

Epidemiology of chancroid and Haemophilus ducreyi in Nairobi, Kenya

Of 300 men in Nairobi, Kenya, with culture-proven chancroid, 57% had acquired infection from prostitutes. The majority of infections were acquired in the city of Nairobi. All 10 female source contacts examined had genital ulcers. 13 of 29 female secondary contacts were culture-positive for Haemophilus ducreyi and 10 of these infected women had clinical chancroid. Of 122 prostitutes from the middle and lower social strata, 12 had genital ulcers, 5 of which were culture-positive for H ducreyi, and a further 5 had symptomless genital carriage of H ducreyi. Prostitutes are a major reservoir of H ducreyi in Nairobi. No evidence of transmission of H ducreyi by women without clinical chancroid was detected.