Complement C3 and marginal zone B cells promote IgG-mediated enhancement of RBC alloimmunization in mice

Administration of anti-RhD immunoglobulin (Ig) to decrease maternal alloimmunization (antibody-mediated immune suppression [AMIS]) was a landmark clinical development. However, IgG has potent immune-stimulatory effects in other settings (antibody-mediated immune enhancement [AMIE]). The dominant thinking has been that IgG causes AMIS for antigens on RBCs but AMIE for soluble antigens. However, we have recently reported that IgG against RBC antigens can cause either AMIS or AMIE as a function of an IgG subclass. Recent advances in mechanistic understanding have demonstrated that RBC alloimmunization requires the IFN-α/-β receptor (IFNAR) and is inhibited by the complement C3 protein. Here, we demonstrate the opposite for AMIE of an RBC alloantigen (IFNAR is not required and C3 enhances). RBC clearance, C3 deposition, and antigen modulation all preceded AMIE, and both CD4+ T cells and marginal zone B cells were required. We detected no significant increase in antigen-specific germinal center B cells, consistent with other studies of RBC alloimmunization that show extrafollicular-like responses. To the best of our knowledge, these findings provide the first evidence of an RBC alloimmunization pathway which is IFNAR independent and C3 dependent, thus further advancing our understanding of RBCs as an immunogen and AMIE as a phenomenon.

Genetic regulation of carnitine metabolism controls lipid damage repair and aging RBC hemolysis in vivo and in vitro

Recent large-scale multi-omics studies suggest that genetic factors influence the chemical individuality of donated blood. To examine this concept, we performed metabolomics analyses of 643 blood units from volunteers who donated units of packed red blood cells (RBCs) on two separate occasions. These analyses identified carnitine metabolism as the most reproducible pathway across multiple donations from the same donor. We also measured L-carnitine and acyl-carnitines in 13,091 packed RBC units from donors in the Recipient Epidemiology and Donor Evaluation (REDS) study. Genome wide association studies against 879,000 polymorphisms identified critical genetic factors contributing to inter-donor heterogeneity in end-of-storage carnitine levels, including common non-synonymous polymorphisms in genes encoding carnitine transporters (SLC22A16, SLC22A5, SLC16A9); carnitine synthesis (FLVCR1, MTDH) and metabolism (CPT1A, CPT2, CRAT, ACSS2), and carnitine-dependent repair of lipids oxidized by ALOX5. Significant associations between genetic polymorphisms on SLC22 transporters and carnitine pools in stored RBCs were validated in 525 Diversity Outbred mice. Donors carrying two alleles of the rs12210538 SLC22A16 Single Nucleotide Polymorphism exhibited the lowest L-carnitine levels, significant elevations of in vitro hemolysis, and the highest degree of vesiculation, accompanied by increases in lipid peroxidation markers. Separation of RBCs by age, via in vivo biotinylation in mice and Percoll density gradients of human RBCs, showed age-dependent depletions of L-carnitine and acyl-carnitine pools, accompanied by progressive failure of the reacylation process following chemically induced membrane lipid damage. Supplementation of stored murine RBCs with L-carnitine boosted post-transfusion recovery, suggesting this could represent a viable strategy to improve RBC storage quality.

Hemolysis and Metabolic Lesion of G6PD Deficient RBCs in Response to Dapsone Hydroxylamine in a Humanized Mouse Model

Glucose 6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy in humans (∼5% of all individuals). G6PD deficiency (G6PDd) is caused by an unstable enzyme and manifests most strongly in red blood cells (RBCs) that cannot synthesize new protein. G6PDd RBCs have decreased ability to mitigate oxidative stress due to lower levels of NADPH, as a result of a defective pentose phosphate pathway. Accordingly, oxidative drugs can result in hemolysis and potentially life-threatening anemia in G6PDd patients. Dapsone is a highly useful drug for treating a variety of pathologies but oral dapsone is contraindicated in patients with G6PDd due to oxidative stress-induced anemia. Dapsone must be metabolized to become hemolytic. Dapsone hydroxylamine (DDS-NOH) has been implicated as the major hemolytic dapsone metabolite, but this has never been tested on G6PDd RBCs with in vivo circulation as a metric. Moreover, the metabolic lesion caused by DDS-NOH is unknown. We report that RBCs from a novel humanized mouse expressing the human Mediterranean G6PD-deficient variant have increased sensitivity to DDS-NOH. In addition, we show that DDS-NOH damaged RBCs can either undergo sequestration (with subsequent return to circulation) or permanent removal in a dose-dependent manner, with G6PD-sufficient RBCs mostly being sequestered, and G6PDd RBCs mostly being permanently removed. Finally, we characterize the metabolic lesion caused by DDS-NOH in G6PDd RBCs and report a blockage in terminal glycolysis resulting in a cellular accumulation of pyruvate. These findings confirm DDS-NOH as a hemolytic metabolite and elucidate metabolic effects of DDS-NOH on G6PDd RBCs. SIGNIFICANCE STATEMENT: These findings confirm that dapsone hydroxylamine, an active metabolite of dapsone, causes in vivo clearance of murine red blood cells expressing a human variant of deficient glucose 6-phosphate dehydrogenase (G6PD), an enzymopathy that affects half a billion individuals (G6PD deficiency). Both cellular mechanisms of clearance (sequestration versus destruction) and specific metabolic disturbances caused by dapsone hydroxylamine are elucidated, providing novel mechanistic understanding.

The role of RBC antigen transgene integration sites on RBC biology in mice

BACKGROUND

Transgenic mice expressing RBC specific antigens are widely used in mechanistic studies of RBC alloimmunization. Existing RBC donor strains have random transgene integration, potentially disrupting host elements that can confound biological interpretation.

STUDY DESIGN AND METHODS

Integration site and genomic alterations were characterized by both targeted locus amplification and congenic backcrossing in the five most commonly used RBC alloantigen donor strains (KEL-K2_hi , KEL-K2_med , and KEL-K2_lo , and KEL-K1). A targeted transgenic approach was developed to allow RBC specific transgene expression from a safe harbor locus (ROSA26). Alloimmune responses were assessed by transfusing alloantigen expressing RBCs into wild-type recipients and measuring alloantibodies by flow cytometry.

RESULTS/FINDINGS

Four of the five analyzed strains had at least one gene disrupted by the transgene integration but none of the disrupted genes are known to be involved in RBC biology. The integration of KEL-K2_med potentially altered the immunological properties of RBCs, although the biological significance of the observed changes is unclear. The ROSA26 targeted approach resulted in a single copy of the transgene that maintains RBC specific expression without random disruption of genomic elements.

CONCLUSION

These findings provide a detailed characterization of genomic disruption by transgene integration found in commonly used RBC donor strains that is relevant to numerous previous publications as well as future studies. With the possible exception of KEL-K2_med , transgene integration is not predicted to affect RBC biology in existing models, and new models can avoid this concern using the described targeted transgenic approach.

Mouse background genetics in biomedical research: The devil's in the details

BACKGROUND

Genetically modified mice are used widely to explore mechanisms in most biomedical fields-including transfusion. Concluding that a gene modification is responsible for a phenotypic change assumes no other differences between the gene-modified and wild-type mice besides the targetted gene.

STUDY DESIGN AND METHODS

To test the hypothesis that the N-terminus of Band3, which regulates metabolism, affects RBC storage biology, RBCs from mice with a modified N-terminus of Band3 were stored under simulated blood bank conditions. All strains of mice were generated with the same initial embryonic stem cells from 129 mice and each strain was backcrossed with C57BL/6 (B6) mice. Both 24-h recoveries post-transfusion and metabolomics were determined for stored RBCs. Genetic profiles of mice were assessed by a high-resolution SNP array.

RESULTS

RBCs from mice with a mutated Band3 N-terminus had increased lipid oxidation and worse 24-h recoveries, "demonstrating" that Band3 regulates oxidative injury during RBC storage. However, SNP analysis demonstrated variable inheritance of 129 genetic elements between strains. Controlled interbreeding experiments demonstrated that the changes in lipid oxidation and some of the decreased 24-hr recovery were caused by inheritance of a region of chromosome 1 of 129 origin, and not due to the modification of Band 3. SNP genotyping of a panel of commonly used commercially available KO mice showed considerable 129 contamination, despite wild-type B6 mice being listed as the correct control.

DISCUSSION

Thousands of articles published each year use gene-modified mice, yet genetic background issues are rarely considered. Assessment of such issues are not, but should become, routine norms of murine experimentation.

Hematologic and systemic metabolic alterations due to Mediterranean class II G6PD deficiency in mice

Deficiency of glucose-6-phosphate dehydrogenase (G6PD) is the single most common enzymopathy, present in approximately 400 million humans (approximately 5%). Its prevalence is hypothesized to be due to conferring resistance to malaria. However, G6PD deficiency also results in hemolytic sequelae from oxidant stress. Moreover, G6PD deficiency is associated with kidney disease, diabetes, pulmonary hypertension, immunological defects, and neurodegenerative diseases. To date, the only available mouse models have decreased levels of WT stable G6PD caused by promoter mutations. However, human G6PD mutations are missense mutations that result in decreased enzymatic stability. As such, this results in very low activity in red blood cells (RBCs) that cannot synthesize new protein. To generate a more accurate model, the human sequence for a severe form of G6PD deficiency, Med(-), was knocked into the murine G6PD locus. As predicted, G6PD levels were extremely low in RBCs, and deficient mice had increased hemolytic sequelae to oxidant stress. Nonerythroid organs had metabolic changes consistent with mild G6PD deficiency, consistent with what has been observed in humans. Juxtaposition of G6PD-deficient and WT mice revealed altered lipid metabolism in multiple organ systems. Together, these findings both establish a mouse model of G6PD deficiency that more accurately reflects human G6PD deficiency and advance our basic understanding of altered metabolism in this setting.

In utero exposure to alloantigens primes alloimmunization to platelet transfusion in mice

BACKGROUND

Platelet transfusions remain a mainstay of treatment for many patients with thrombocytopenia, but can lead to alloantibodies to Human Leukocyte Antigens (anti-HLA) resulting in inadequate responses to subsequent platelet transfusions (refractoriness), as well as complicate transplantation. Despite substantial decreases in alloimmunization with the implementation of leukoreduction, a significant percentage of patients still become alloimmunized following platelet transfusions. It remains unclear why some patients make anti-HLA antibodies, but others do not make anti-HLA antibodies even with chronic transfusion. Antecedent pregnancy correlates with risk of alloimmunization due to platelet transfusion in humans - however, isolation of pregnancy as a single variable is not possible in human populations.

STUDY DESIGN AND METHODS

A tractable murine model of pregnancy and transfusion was engineered by breeding C57BL/6 (H-2b ) dames with BALB/c (H-2d ) sires. After pregnancy, female mice were transfused with leukoreduced platelets from F1 (H-2b/d ) donors that expressed the same paternal major histocompatibility complex (MHC) H-2d alloantigens as the sires. Control groups allowed isolation of pregnancy or transfusion alone as independent variables. Alloimmunization was determined by testing serum for antibodies to H-2d MHC alloantigens.

RESULTS

No alloantibodies were detected after pregnancy alone, or in response to transfusion of platelets alone; however, significant levels of alloantibodies were detected when pregnancy was followed by transfusion.

CONCLUSIONS

These findings isolate antecedent pregnancy as a causal contribution to increased frequencies of alloimmunization by subsequent platelet transfusion in mice and provide a platform for ongoing mechanistic investigation.

Complement activation on endothelium initiates antibody-mediated acute lung injury

Antibodies targeting human leukocyte antigen (HLA)/major histocompatibility complex (MHC) proteins limit successful transplantation and transfusion, and their presence in blood products can cause lethal transfusion-related acute lung injury (TRALI). It is unclear which cell types are bound by these anti-leukocyte antibodies to initiate an immunologic cascade resulting in lung injury. We therefore conditionally removed MHC class I (MHC I) from likely cellular targets in antibody-mediated lung injury. Only the removal of endothelial MHC I reduced lung injury and mortality, related mechanistically to absent endothelial complement fixation and lung platelet retention. Restoration of endothelial MHC I rendered MHC I-deficient mice susceptible to lung injury. Neutrophil responses, including neutrophil extracellular trap (NET) release, were intact in endothelial MHC I-deficient mice, whereas complement depletion reduced both lung injury and NETs. Human pulmonary endothelial cells showed high HLA class I expression, and posttransfusion complement activation was increased in clinical TRALI. These results indicate that the critical source of antigen for anti-leukocyte antibodies is in fact the endothelium, which reframes our understanding of TRALI as a rapid-onset vasculitis. Inhibition of complement activation may have multiple beneficial effects of reducing endothelial injury, platelet retention, and NET release in conditions where antibodies trigger these pathogenic responses.

IgG Subclass Determines Suppression Versus Enhancement of Humoral Alloimmunity to Kell RBC Antigens in Mice

It has long been appreciated that immunoglobulins are not just the effector endpoint of humoral immunity, but rather have a complex role in regulating antibody responses themselves. Donor derived anti-RhD IgG has been used for over 50 years as an immunoprophylactic to prevent maternal alloimmunization to RhD. Although anti-RhD has dramatically decreased rates of hemolytic disease of the fetus and newborn (for the RhD alloantigen), anti-RhD also fails in some cases, and can even paradoxically enhance immune responses in some circumstances. Attempts to generate a monoclonal anti-RhD have largely failed, with some monoclonals suppressing less than donor derived anti-RhD and others enhancing immunity. These difficulties likely result, in part, because the mechanism of anti-RhD remains unclear. However, substantial evidence exists to reject the common explanations of simple clearance of RhD + RBCs or masking of antigen. Donor derived anti-RhD is a mixture of 4 different IgG subtypes. To the best of our knowledge an analysis of the role different IgG subtypes play in immunoregulation has not been carried out; and, only IgG1 and IgG3 have been tested as monoclonals. Multiple attempts to elicit alloimmune responses to human RhD epitopes in mice have failed. To circumvent this limitation, we utilize a tractable animal model of RBC alloimmunization using the human Kell glycoprotein as an antigen to test the effect of IgG subtype on immunoregulation by antibodies to RBC alloantigens. We report that the ability of an anti-RBC IgG to enhance, suppress (at the level of IgM responses), or have no effect is a function of the IgG subclass in this model system.

Impact of taurine on red blood cell metabolism and implications for blood storage

BACKGROUND

Taurine is an antioxidant that is abundant in some common energy drinks. Here we hypothesized that the antioxidant activity of taurine in red blood cells (RBCs) could be leveraged to counteract storage-induced oxidant stress.

STUDY DESIGN AND METHODS

Metabolomics analyses were performed on plasma and RBCs from healthy volunteers (n = 4) at baseline and after consumption of a whole can of a common, taurine-rich (1000 mg/serving) energy drink. Reductionistic studies were also performed by incubating human RBCs with taurine ex vivo (unlabeled or ¹³ C¹⁵ N-labeled) at increasing doses (0, 100, 500, and 1000 μmol/L) at 37°C for up to 16 hours, with and without oxidant stress challenge with hydrogen peroxide (0.1% or 0.5%). Finally, we stored human and murine RBCs under blood bank conditions in additives supplemented with 500 μmol/L taurine, before metabolomics and posttransfusion recovery studies.

RESULTS

Consumption of energy drinks increased plasma and RBC levels of taurine, which was paralleled by increases in glycolysis and glutathione (GSH) metabolism in the RBC. These observations were recapitulated ex vivo after incubation with taurine and hydrogen peroxide. Taurine levels in the RBCs from the REDS-III RBC-Omics donor biobank were directly proportional to the total levels of GSH and glutathionylated metabolites and inversely correlated to oxidative hemolysis measurements. Storage of human RBCs in the presence of taurine improved energy and redox markers of storage quality and increased posttransfusion recoveries in FVB mice.

CONCLUSION

Taurine modulates RBC antioxidant metabolism in vivo and ex vivo, an observation of potential relevance to transfusion medicine.

Repeated gestational exposure of mice to chlorpyrifos oxon is associated with paraoxonase 1 (PON1) modulated effects in maternal and fetal tissues

Chlorpyrifos oxon (CPO), the toxic metabolite of the organophosphorus (OP) insecticide chlorpyrifos, causes developmental neurotoxicity in humans and rodents. CPO is hydrolyzed by paraoxonase-1 (PON1), with protection determined by PON1 levels and the human Q192R polymorphism. To examine how the Q192R polymorphism influences fetal toxicity associated with gestational CPO exposure, we measured enzyme inhibition and fetal-brain gene expression in wild-type (PON1(+/+)), PON1-knockout (PON1(-/-)), and tgHuPON1R192 and tgHuPON1Q192 transgenic mice. Pregnant mice exposed dermally to 0, 0.50, 0.75, or 0.85 mg/kg/d CPO from gestational day (GD) 6 through 17 were sacrificed on GD18. Biomarkers of CPO exposure inhibited in maternal tissues included brain acetylcholinesterase (AChE), red blood cell acylpeptide hydrolase (APH), and plasma butyrylcholinesterase (BChE) and carboxylesterase (CES). Fetal plasma BChE was inhibited in PON1(-/-) and tgHuPON1Q192, but not PON1(+/+) or tgHuPON1R192 mice. Fetal brain AChE and plasma CES were inhibited in PON1(-/-) mice, but not in other genotypes. Weighted gene co-expression network analysis identified five gene modules based on clustering of the correlations among their fetal-brain expression values, allowing for correlation of module membership with the phenotypic data on enzyme inhibition. One module that correlated highly with maternal brain AChE activity had a large representation of homeobox genes. Gene set enrichment analysis revealed multiple gene sets affected by gestational CPO exposure in tgHuPON1Q192 but not tgHuPON1R192 mice, including gene sets involved in protein export, lipid metabolism, and neurotransmission. These data indicate that maternal PON1 status modulates the effects of repeated gestational CPO exposure on fetal-brain gene expression and on inhibition of both maternal and fetal biomarker enzymes.

Models for assessing antipsychotics: antagonism of amphetamine-induced hyperactivity and stereotypies in mice

All classical antipsychotics, such as chlorpromazine and haloperidol, have potent dopamine receptor-blocking properties. This unit describes the rat anti-Thy-1.1 model of acute proliferative glomerulonephritis for the study of chronic renal insufficiency. A procedure is detailed for the induction of glomerulonephritis in rats as well as measurement of daily urinary excretion of protein, which is a convenient, primary screening tool. The unit also provides methods for assessment of glomerular filtration rate and effective renal plasma flow in anesthetized rats with anti-Thy-1.1-induced renal insufficiency.

Omentoplasty in abdominoperineal resection of the rectum

An omental pedicle graft, based on the right gastro-epiploic artery to facilitate perineal healing, was used in 20 cases of abdominoperineal resection of the rectum. There was one postoperative death. Primary healing of the perineum occurred in all cases. The technique is described and recommended.

A comparison between diuresis renography and the Whitaker test in 64 kidneys

Fifty-seven patients have provided 64 dilated pelvicaliceal units for study by diuresis renography and the Whitaker test. Of 45 kidneys showing a type I or type IIIa renographic response (unobstructed), 32 were, according to Whitaker's criteria, obstructed, 8 fell into an equivocal zone and only 5 were unobstructed. Thirty-five of these kidneys--33 of which were associated with moderate or severe loin pain--were operated on for presumed obstruction with generally excellent symptomatic and renographic result. Thus the detection of a type I or type IIIa response in a dilated, painful system cannot be taken to exclude obstruction. Better correlation was obtained between renography and the Whitaker test in patients exhibiting a type IIIb or type II renographic response. Diuresis renography is a sensitive indicator of urodynamic disturbance in the upper urinary tract and an ideal means of evaluating post-operative progress. The Whitaker test provides a reliable means of selecting patients who will benefit from pyeloplasty.

Renal tubular damage without glomerular damage after cytotoxic drugs and aminoglycosides

Cytotoxic agents and aminoglycosides when given for a maximum of eleven days damaged the renal tubules as indicated by an increased urinary beta 2-microglobulin (beta 2-m), N-acetyl-beta-D-glucosaminidase (NAG) and total protein. Methotrexate (MTX) caused the greatest changes among the cytotoxic agents studied. Prophylactic doses of aminoglycosides in surgical patients also caused tubuloproteinuria. The tubular damage was greatest when aminoglycosides were given to treat septicaemia complicating haematological malignancies in patients who had previously had cytotoxic drugs. However, even in these patients there was no evidence of glomerular failure or increased glomerular permeability seven days after beginning chemotherapy.

Effect of metoclopramide on guinea pig stomach: critical dependence on intrinsic stores of acetylcholine

This study is concerned with an investigation of the hypothesis that metoclopramide enhances the contractile activity of the guinea pig antrum by increasing acetylcholine release from the postganglionic cholinergic nerve ending. Longitudinal muscle strips were stimulated repetitively (200 microseconds pulses, 20 Hz, supra maximal current) for 2 hr in the presence of hemicholinium-3 (200 micron). Pretreatment in this manner produced a mean reduction of 50% in the acetylcholine content, when compared with that in repetitively stimulated control strips not incubated with hemicholinium-3. In the hemicholinium-3-treated strips the normal excitatory response to metoclopramide (60 micrometer) was prevented. Only a small reduction in response to metoclopramide was detected in strips which were incubated with hemicholinium-3 but not stimulated repetitively, and in which there was no significant change in acetylcholine content. The stimulant effect of metoclopramide depends, therefore, upon maintenance of intrinsic stores of acetylcholine.

Pharmacological analysis of the effects of metoclopramide on the guinea pig isolated stomach

A pharmacological analysis has been made of the effects of metoclopramide on the contractile activity of isolated longitudinal muscle strips prepared from the guinea pig stomach. Metoclopramide produced up to 3-fold increases in the amplitude of the spontaneous contractions exhibited by such a preparation. This phenomenon was antagonized by hyoscine but not by tetrodotoxin nor by hexamethonium. The contractile response to transmural stimulation was also enhanced by metoclopramide, as was the response to extrinsic acetylcholine. Neural inhibitory systems were not affected by metoclopramide. The apparent sensitization to extrinsic acetylcholine was, however, prevented by tetrodotoxin and hexamethonium, implying that this effect depends upon ganglionic stimulation by acetylcholine. These results suggest that metoclopramide may act by increasing the amount of acetylcholine released at the postgangionic cholinergic nerve ending.

Albumin metabolism: effect of the nutritional state and the dietary protein intake

Nine malnourished and nine children who had recovered from malnutrition were given a single injection of albumin-(131)I and were studied during consecutive periods in which the dietary protein was changed.Malnourished children had significantly lower catabolic rates of albumin than had recovered children on the same protein intake. Both nutritional groups, however, showed a progressive fall in catabolic rate after 3-5 days on a low protein diet (0.7-1.0 g/kg per day), and the maximum effect was seen in the 2nd wk of low protein feeding. The catabolic rate could return to normal within 3 wk in a malnourished child fed 4 g of protein/kg per day. The albumin synthetic rate was measured by a computer technique suitable for nonsteady-state conditions. The synthetic rate in the malnourished groups (101 mg/kg per day) fed on a low protein diet was significantly lower than the rate in the recovered groups (148 mg/kg per day). The synthetic rate responded rapidly to a change in diet; when the rate fell, the intravascular albumin mass was maintained by two compensating mechanisms: (1) a net transfer of extravascular albumin into the intravascular pool; and (2) by a delayed fall in the catabolic rate. The net transfer of albumin into the intravascular compartment diminished as the catabolic rate fell. ADAPTATION TO A LOW PROTEIN DIET WAS ASSOCIATED WITH: (a) low synthetic and catabolic rates of albumin; (b) a reduced extravascular albumin mass; and (c) a capacity for a rapid return to normal in the synthetic rate when the dietary protein was increased.