Defects in B-cell function and metabolism in uremia: role of parathyroid hormone

Safety and immediate humoral response of COVID-19 vaccines in chronic kidney disease patients: the SENCOVAC study

Background

Chronic kidney disease (CKD) patients are at high-risk for severe Covid-19. The multicentric, observational and prospective SENCOVAC study aims to describe the humoral response and safety of SARS-CoV-2 vaccines in CKD patients. Safety and immediate humoral response results are reported here.

Methods

Four cohorts of patients were included: kidney transplant (KT) recipients, haemodialysis (HD), peritoneal dialysis (PD) and non-dialysis CKD patients from 50 Spanish centres. Adverse events after vaccine doses were recorded. At baseline and on day 28 after the last vaccine dose, anti-Spike antibodies were measured and compared between cohorts. Factors associated with development of anti-Spike antibodies were analyzed.

Results

1746 participants were recruited: 1116 HD, 171 PD, 176 non-dialysis CKD patients and 283 KT recipients. Most patients (98%) received mRNA vaccines. At least one vaccine reaction developed after the first dose in 763 (53.5%) and after the second dose in 741 (54.5%) of patients. Anti-Spike antibodies were measured in the first 301 patients. At 28 days, 95% of patients had developed antibodies: 79% of KT, 98% of HD, 99% of PD and 100% of non-dialysis CKD patients (p<0.001). In a multivariate adjusted analysis, absence of an antibody response was independently associated to KT (OR 20.56, p = 0.001) and to BNT162b2 vaccine (OR 6.03, p = 0.023).

Conclusion

The rate of anti-Spike antibody development after vaccination in KT patients was low but in other CKD patients it approached 100%; suggesting that KT patients require persistent isolation measures and booster doses of a Covid-19 vaccine. Potential differences between Covid-19 vaccines should be explored in prospective controlled studies.

Beyond Bone: Infectious Diseases and Immunity in Parathyroid Disorders

Parathyroid disorders are characterized by alterations in calcium and phosphate homeostasis due to inappropriately high or low levels of parathyroid hormone (PTH). Despite PTH receptor type 1 has been described in almost all immune lineages and calcium signalling has been confirmed as a crucial mediator for immune response, in vitro studies on the physiological interactions between PTH and immunity are conflicting and not representative of the clinical scenarios seen in patients with parathyroid disorders. Infectious diseases are among the main causes of increased morbidity and mortality in patients with secondary hyperparathyroidism and chronic kidney disease. More, immune alterations have been described in primary hyperparathyroidism. Recent studies have unveiled an increased risk of infections also in hypoparathyroidism, suggesting that not only calcium, but also physiological levels of PTH may be necessary for a proper immune response. Finally, calcium/phosphate imbalance could affect negatively the prognosis of infectious diseases. Our review aimed to collect available data on infectious disease prevalence in patients with parathyroid disorders and new evidence on the role of PTH and calcium in determining the increased risk of infections observed in these patients.

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Immune Dysfunction and Risk of Infection in Chronic Kidney Disease

Cardiovascular disease and infections are directly or indirectly associated with an altered immune response, which leads to a high incidence of morbidity and mortality, and together, they account for up to 70% of all deaths among patients with chronic kidney dysfunction. Impairment of the normal reaction of the innate and adaptive immune systems in chronic kidney disease predisposes patients to an increased risk of infections, virus-associated cancers, and a diminished vaccine response. On the other hand, an abnormal, exaggerated reaction of the immune systems can also occur in this group of patients, resulting in increased production and decreased clearance of proinflammatory cytokines, which can lead to inflammation and its sequelae (eg, atherosclerotic cardiovascular disease). Epigenetically, modifications in hematopoietic stem cells involving a shift from lymphoid to myeloid cell lineage may underlie uremia-associated immunological senescence, which is not reversed by renal replacement therapy, including kidney transplantation. Measures aimed at attenuating the immune abnormalities in chronic kidney disease/end-stage renal disease should be an area of focused research as this could potentially lead to a better understanding and, thus, development of therapies that could reduce the disastrously high death rate in this patient population. The aim of the present article is to review the characteristics, causes, and mechanisms of the immune dysfunction related to chronic kidney disease.

Underlying renal insufficiency: the pivotal risk factor for Pneumocystis jirovecii pneumonia in immunosuppressed patients with non-transplant glomerular disease

PURPOSES

Data on PCP in patients with glomerular disease are rare. The aim of this study was to assess the predictors of PCP development, the risk factors for mortality and the incidence of acute kidney injury (AKI) when high-dose trimethoprim-sulphamethoxazole (TMP-SMX) was used in patients with non-transplant glomerular disease.

METHODS

Forty-seven patients with PCP, as confirmed by positive results for Pneumocystis jirovecii DNA or Pneumocystis jirovecii cysts tested by a methenamine silver stain between January 1, 2003, and December 30, 2012, were retrospectively investigated. The baseline characteristics of glomerular disease, clinical findings of PCP and renal parameters after treatment were collected. Predictors for PCP development and risk factors for mortality were determined using a multivariate logistic regression analysis.

RESULTS

All PCP patients exclusively received immunosuppressants. Baseline renal insufficiency [estimated glomerular filtration rate (eGFR) <60 mL/min·1.73 m²] was present in 87.23 % of patients. The overall mortality rate was 29.79 %. A pulmonary coinfection and the need for mechanical ventilation were independently associated with PCP mortality. A lower eGFR, lower serum albumin level and a higher percentage of global glomerulosclerosis were independent predictors of PCP in patients with IgA nephropathy receiving immunosuppressants. AKI occurred in 60.47 % of patients who received TMP-SMX. After treatment cessation, 93.75 % of surviving patients showed a recovery of renal function to baseline values.

CONCLUSIONS

PCP is a fatal complication in patients with glomerular disease, and the use of immunosuppressants may be a basic risk factor for this infection. Underlying renal insufficiency and high renal pathology chronicity are the key risk factors for PCP in IgA nephropathy. TMP-SMX therapy remains an ideal choice because of high treatment response and frequently reversible kidney injury.

Toll-like receptors TLR4 (Asp299Gly and Thr399Ile) and TLR2 (Arg677Trp and Arg753Gln) gene polymorphisms in end-stage renal disease patients on peritoneal dialysis

BACKGROUND

Toll-like receptors (TLRs), expressed on cells of the innate immune system, are the first line of host defense. Recognition of bacterial pathogens by the peritoneum is mediated in part by TLR. In this study, we investigated the role of TLR4 (Asp299Gly and Thr399Ile) and TLR2 (Arg677Trp and Arg753Gln) gene polymorphisms in end-stage renal disease (ESRD) patients on peritoneal dialysis (PD).

METHOD

A total of 100 ESRD patients on PD and 150 healthy controls were enrolled in the study. The patients were divided into two groups: ESRD patients on PD with peritonitis (n = 38) and without peritonitis (n = 62). Genotyping of TLR4 (Asp299Gly and Thr399Ile) and TLR2 (Arg677Trp and Arg753Gln) genes were performed by polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP).

RESULTS

Heterozygous variant of TLR4 (Thr399Ile) Thr/Ile genotype showed significant association with both groups of patients (patients with and without peritonitis) with no difference between the groups. Overall, TLR4 (Thr399Ile) Thr/Ile genotype demonstrated an association with ESRD on PD (OR 3.9). Further, TLR4 (Thr399Ile) polymorphism showed significant association with PD patients having two or more episodes of peritonitis compared to patients with no peritonitis. No such association of increased risk of ESRD was observed with TLR4 (Asp299Gly) Asp/Gly genotype and TLR2 polymorphisms. Haplotype frequencies, Gly/Ile and Asp/Ile, conferred 2.46- and 4.62-fold increased risk of ESRD, respectively.

CONCLUSIONS

TLR4 Thr399Ile genotype was associated with ESRD patients on PD; however, the genotype frequency was similar in PD patients with and without peritonitis.

Serum vitamin D levels are positively associated with varicella zoster immunity in chronic dialysis patients

Uremia results in a relatively immunocompromised status, and patients under chronic dialysis have an elevated risk of developing herpes zoster (HZ). We sought to investigate the relationship between vitamin D status and immunity to varicella-zoster virus (VZV). A multicenter prevalent hemodialysis cohort was assembled between 2012 and 2013. We assayed the biochemical parameters, 25-hydroxy- (25-OH-D) and 1,25-dihydroxyvitamin D, vitamin D-binding protein levels in the sera. VZV immunity was quantitated using VZV-specific glycoprotein IgG and IgM titers. Eighty-eight patients were enrolled and their sera were analyzed. Chronic hemodialysis patients with 25-OH-D < 30 ng/ml (insufficiency or deficiency) had significantly lower VZV-IgG than those with sufficient 25-OH-D (p = 0.04). This discrepancy became more prominent if active vitamin D users alone were analyzed (p = 0.01). Generalized additive modeling showed that those with 25-OH-D higher than 27.8 ng/ml or bioavailable 25-OH-D higher than 3.88 ng/ml had significantly higher VZV-IgG levels than those with lower values. Linear regression suggested that both total and bioavailable 25-OH-D were significantly associated with higher VZV-IgG levels (p = 0.003 [total] and 0.01 [bioavailable]), whereas patients with cancer had lower VZV-IgG. Vitamin D may therefore be a potentially useful choice for raising VZV immunity in chronic dialysis patients.

Iron sucrose impairs phagocytic function and promotes apoptosis in polymorphonuclear leukocytes

BACKGROUND

With the recent implementation of bundling reimbursement policy, the use of intravenous (IV) iron preparations for the management of anemia in the end-stage renal disease (ESRD) population has dramatically increased. Iron overload increases the risk of infections in individuals with or without kidney disease. IV iron administration in ESRD patients impairs bacteriocidal capacity of polymorphonuclear leukocytes (PMNs) against Escherichia coli. These preparations consist of an elemental iron core and a carbohydrate shell. In addition to the iron core, the carbohydrate shell may affect PMNs. We therefore examined the effect of iron sucrose, a commonly used preparation, on phagocytic capacity of PMNs from a group of normal individuals against Gram-positive (Staphylococcus aureus) and Gram-negative (E. coli) bacteria.

METHODS

Iron sucrose was added to heparinized blood samples at pharmacologically-relevant concentrations and incubated for 4 and 24 h at 37°C to simulate in vivo condition. Blood samples mixed with equal volume of saline solution served as controls. To isolate the effects of the carbohydrate shell, blood samples were co-treated with the iron chelator, desferrioxamine.

RESULTS

Iron sucrose caused significant PMN apoptosis and dose-dependent suppression of phagocytic function against both Gram-positive and Gram-negative bacteria. These abnormalities were prevented by desferrioxamine which precluded contribution of the carbohydrate shell to the PMN dysfunction.

CONCLUSIONS

At pharmacologically-relevant concentrations, iron sucrose promotes apoptosis and inhibits phagocytic activities of PMNs. The deleterious effect of iron sucrose is mediated by its elemental iron core, not its carbohydrate shell, and as such may be shared by other IV iron preparations.

Effect of uremia on structure and function of immune system

End-stage renal disease (ESRD) is simultaneously associated with immune activation, marked by systemic inflammation, and immune deficiency. Systemic inflammation contributes to atherosclerosis, cardiovascular disease, cachexia, and anemia, whereas immune deficiency leads to impaired response to vaccination, and increased incidence and severity of microbial infections. ESRD-associated inflammation and immune deficiency are associated with the following: (a) general expansion of monocytes and elevations of their basal integrin, Toll-like receptor (TLR)-2, TLR-4 expression, cytokine production, and reactive oxygen species (ROS) generation and reduced phagocytic capacity, (b) depletion and impaired inhibitory activity of regulatory T cells, (c) spontaneous activation, degranulation, increased basal ROS production, decreased phagocytic capacity, and increased apoptosis of the circulating polymorphonuclear leukocytes, (d) upregulation of ROS production machinery and chemokine expression in the cellular constituents of various tissues, highlighting participation of nonimmune cells in the prevailing inflammatory state, (e) depletion of the antigen-presenting dendritic cells, (f) reduced CD4/CD8 T cell ratio and depletion of naïve and central memory T cells, (g) diffuse B cell lymphopenia leading to impaired humoral immunity, and (h) increased proinflammatory activity of low-density lipoprotein and reduced anti-inflammatory capacity of high-density lipoprotein. Thus, ESRD-associated inflammation is due to activation of innate immune system, orchestrated by monocytes, macrophages, granulocytes, and cellular constituents of other organs/tissues. This is coupled with immune deficiency that is caused by depletion of dendritic cells, naïve and central memory T cells and B cells, and impaired phagocytic function of polymorphonuclear leukocytes and monocytes.

The role of mast cells in parathyroid bone disease

Chronic hyperparathyroidism (HPT) is a common cause of metabolic bone disease. These studies investigated the underlying cellular and molecular mechanisms responsible for the detrimental actions of elevated parathyroid hormone (PTH) on the skeleton. Bone biopsies from hyperparathyroid patients revealed an association between parathyroid bone disease and increased numbers of bone marrow mast cells. We therefore evaluated the role of mast cells in the etiology of parathyroid bone disease in a rat model for chronic HPT. In rats, mature mast cells were preferentially located at sites undergoing bone turnover, and the number of mast cells at the bone-bone marrow interface was greatly increased following treatment with PTH. Time-course studies and studies employing parathyroid hormone-related peptide (PTHrP), as well as inhibitors of platelet-derived growth factor-A (PDGF-A, trapidil), kit (gleevec), and PI3K (wortmannin) signaling revealed that mature mast cell redistribution from bone marrow to bone surfaces precedes and is associated with osteitis fibrosa, a hallmark of parathyroid bone disease. Importantly, mature mast cells were not observed in the bone marrow of mice. Mice, in turn, were resistant to the development of PTH-induced bone marrow fibrosis. These findings suggest that the mast cell may be a novel target for treatment of metabolic bone disease.

Effect of end-stage renal disease on B-lymphocyte subpopulations, IL-7, BAFF and BAFF receptor expression

BACKGROUND

End-stage renal disease (ESRD) results in increased susceptibility to infections, impaired response to vaccination and diffuse B-cell lymphopenia. However, the precise nature and mechanism of ESRD-induced B-cell lymphopenia remains unclear. Therefore, we studied the distribution of major B-cell subsets, B-cell growth, differentiation and survival factors, IL-7 and BAFF, and their receptors in 21 haemodialysis patients and 21 controls.

METHODS

Innate B1 cells (CD19+, CD5+), conventional B2 cells (CD19+, CD5-), newly formed transitional B cells (CD19+, CD10+, CD27-), naïve B cells (CD19+, CD27-) and memory B cells (CD19+, CD27+) and BAFF receptor were quantified by flow cytometry. Plasma IL-7, BAFF, IL-6, TNF-alpha and IL-10 were measured by ELISA.

RESULTS

The ESRD group exhibited significant reductions of all B-cell subpopulations except for transitional B cells that were less severely affected. No significant difference was found in B-cell apoptosis between the ESRD and control groups. Moreover, plasma IL-7 and BAFF levels were elevated in ESRD patients, therefore excluding their deficiencies as a possible culprit. However, BAFF receptor expression was significantly reduced in transitional but not mature B cells in the ESRD group. Interestingly, B-cell activation with the TLR9 agonist resulted in significantly greater production of IL-6 and TNF alpha but not IL-10 in the ESRD group.

CONCLUSIONS

Thus, despite elevation of B-cell growth, differentiation and survival factors, ESRD patients exhibited diffuse reduction of B-cell subpopulations. This was associated with the down-regulation of BAFF receptor in transitional B cells. The latter can, in part, contribute to B-cell lymphopenia by promoting resistance to the biological actions of BAFF that is a potent B-cell differentiation and survival factor.

Naïve and central memory T-cell lymphopenia in end-stage renal disease

End-stage renal disease (ESRD) is associated with increased propensity to infections, diminished response to vaccination, impaired cell-mediated immunity, and reduced CD4+/CD8+ T-lymphocyte ratio. Four subsets of CD4+ and CD8+ T cells have been recently identified: naïve cells (as yet uncommitted), central memory (CM) cells (previously programmed), and CD45RA-positive and CD45RA-negative effector memory (EM) cells (programmed to perform specific effector functions). The effect of ESRD on subpopulations of T lymphocytes is unclear and was studied here. Twenty-one hemodialysis patients and 21 age-matched controls were studied. Pre- and post-dialysis blood samples were obtained and analyzed by three-color flow cytometry. CD4+/CD8+ ratio and the numbers of the naïve and CM CD4+ and CD8+ T cells were significantly reduced, whereas the numbers of EM CD4+ and CD8+ T cells were unchanged in the ESRD group. The reduction of the naïve and CM T-cell counts in the ESRD group was associated with increased apoptosis of these cells. Negative correlations were found between severity of azotemia, oxidative stress, and hyperphosphatemia with the number of naïve T cells. Comparison of diabetic with non-diabetic ESRD patients revealed higher numbers of total CD8+ cells and EM CD8+ T cells in the diabetic group. Dialysis did not significantly change the naïve and CM CD4+ or CD8+ cell counts, but significantly lowered CD8+ EM cell count. Thus, ESRD results in increased apoptosis and diminished populations of naïve and CM T lymphocytes. This phenomenon may, in part, contribute to the impaired immune response in this population.

Interleukin-6 production and secretion by human parathyroids

Parathyroid hormone (PTH) stimulates osteoblasts to produce the proinflammatory cytokine interleukin-6 (IL-6), causing bone resorption. In patients with primary hyperparathyroidism, elevated serum levels of IL-6 normalize after resection of parathyroid tumours. Because IL-6 is also expressed in normal parathyroids and in other endocrine cells (adrenal and islet), we hypothesized that parathyroid tumours might contribute directly to the elevated serum IL-6 levels in patients with hyperparathyroidism. Immunohistochemistry identified IL-6, PTH, and chromogranin-A (an endocrine and neuroendocrine tumour marker) in normal, adenomatous and hyperplastic parathyroids. Using immunofluorescence and confocal microscopy, IL-6 co-localized with PTH and with chromogranin-A in parathyroid cells. All cultured parathyroid tumours secreted IL-6 at levels markedly higher than optimally stimulated peripheral blood mononuclear cells. Supernates from cultured parathyroids stimulated proliferation of an IL-6-dependent cell line, and anti-IL-6 MoAb abolished this stimulatory effect. IL-6 mRNA was documented in cultured parathyroid tumours, cultured normal parathyroids, fresh operative parathyroid tumours and fresh operative normal specimens. In conclusion, these data show that parathyroid tumours and normal parathyroids contain, produce and secrete IL-6. Our findings present a novel pathway by which human parathyroids may contribute markedly to IL-6 production and elevation of serum IL-6 levels in patients with hyperparathyroidism. The physiological relevance of IL-6 production by human parathyroids remains to be determined, but IL-6 secretion by parathyroid tumours may contribute to bone loss and to other multi-system complaints observed in these patients.