Profiling peripheral B-cell subtypes most predictive for cardiac allograft rejection

Introduction

B-cells have been strongly implicated in cardiac allograft rejection (CAR). Recently, however, the CTOT-11 trial showed that depleting mature CD20+ B-cells did not reduce rates of rejection in cardiac allograft recipients and unexpectedly increased the severity of allograft vasculopathy. Therefore, it can be hypothesized that differing phenotypic subtypes of B-cells correspond with different biological mechanisms relating to CAR. Though, current applications to quantify these subtypes of immune cells, i.e with immunohistochemistry or flow cytometry, are often restricted by limited cell markers and cost-burden; therefore, we demonstrate a novel deconvolution method, FARDEEP, that has been validated to accurately enumerate peripheral blood mononuclear cell-subtypes (PBMCs) in a quicker and more cost-effective manner.

Purpose

To better understand the association of different B-cell subtypes in CAR by identifying the B-cell subtype most predictive for pathologically defined rejection.

Methods

The machine learning tool, FARDEEP, was trained with the transcriptomic signatures of 29 PBMC subtypes, characterized by previous single-cell RNA experiments. FARDEEP then was used to deconvolute data-mined RNA from 259 blood samples from 98 cardiac allograft recipients enrolled in the CARGO study (GSE2445). Random forest tree (RF) was then used to analyze the levels of deconvoluted subtypes to predict the severity of rejection assessed by endomyocardial biopsy. Finally, RF was used to identify the subtypes of PBMCs most valuable in predicting rejection.

Results

Out of the 259 samples with consensus pathological readings, 140 had a consensus International Society of Heart and Lung Transplant grade of 0, 63 with grade 1a, 31 with grade 1b, and 25 with grade 3a or higher. We grouped biopsy samples with grade 0, 1a, and 1b as “low-risk” rejection (n=234). 3a or higher samples were grouped as “high-risk” (n=25). There were no grade 2s in the dataset. According to the dataset, blood was extracted from patients on average 72.5 days post-transplant. The RF had good performance in predicting rejection severity. (Figure 1a) CD20- plasmablast cells were stronger predictors for differentiating high-risk from low-risk compared to CD20+ B-cell populations (i.e B Naive and B Memory cells). (Figure 1b) Overall, however, dendritic cells (DCs), neutrophils, monocytes, and basophils were the strongest predictors for rejection.

Conclusion

Our findings support the results from the CTOT-11 trial showing that CD20+ B-cells may not contribute to CAR as significantly as seen with other PBMC subtypes. Instead, we showed that among B-cells, CD20- plasmablasts were more likely associated with CAR, possibly explaining why targeting CD20 was ineffective in preventing rejection. Thus, targeting plasmablast-associated markers could potentially be more useful to prevent CAR.

Model Performance with Variables

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): 1) Society of Academic Emergency Medicine Foundation; 2) The Jewish Fund

Extrapontine myelinolysis and cortical laminar necrosis caused by severe hypernatremia following peritoneal lavage for ruptured hydatid cyst of the liver. A case report and review of the literature

Extrapontine myelinolysis (EPM) and cortical laminar necrosis (CLN) have rarely been reported in association with severe hypernatremia. We describe a patient with EPM associated with CLN following severe hypernatremia due to hypertonic peritoneal lavage after a ruptured hydatid cyst of the liver. Clinical and neuroimaging findings in acute stage and serial brain MRI at two and five month follow-up are discussed in detail.

GB virus C/hepatitis G virus infection in Saudi Arabian blood donors and patients with cryptogenic hepatitis

Viral hepatitis is a common infection in the developing countries. Aside from Hepatitis A-E viruses, a novel hepatitis virus termed GBV-C, or HGV, was recently described. We have studied the prevalence of this virus among Saudi Arabian healthy blood donors (n = 200) and patients with cryptogenic (non-A-E) hepatitis (n=71). After serum extraction and RNA reverse transcription, amplification was carried out by the polymerase chain reaction (PCR), using primers for the 5' noncoding region (NCR), NS5A region and NS3 helicase region. Among the patients with cryptogenic hepatitis, PCR-positivity was 18/71 (25.4%) for the 5' NCR, 14/71 (19.7%) for the NS5A region, and 15/71 (21.1%) for the NS3 helicase region. Among the healthy blood donors, PCR-positivity was 4/200 (2%) for the 5' NCR, 0/200 (0%) for the NS5A region, and 1/200 (0.5%) for the NS3 helicase region. Since the 5' NCR is considered the most conserved segment of the virus genome, it is not unusual to find higher positivity rate when that region is used for amplification. It is noted that the positivity rate is not far different among the three amplified regions, indicating that the heterogeneity of GBV-C/HGV is not as extensive as in hepatitis C virus. Phylogenetic analysis of 5'NCR DNA sequences showed that all isolates in this study belong to genotype 2. We conclude that the prevalence of GBV-C/HGV is similar to what is reported worldwide among the general Saudi population but relatively higher among Saudi patients with cryptogenic hepatitis.

Downregulation of tyrosinase activity in human melanocyte cell cultures by yohimbine

Treatment of human melanocyte cell cultures with the alpha-2 adrenergic receptor antagonist yohimbine results in a marked down-regulation of tyrosinase activity. A 30% decrease occurs within 12 h of exposure of cells to yohimbine (100 microM), and by 48 h tyrosinase activity in treated melanocytes is less than a fifth that of control cultures. The inhibition is dose dependent and occurs in human melanocytes derived from either black or white skin types, and also in mouse melanoma cells. The yohimbine-induced decrease in tyrosinase activity is reversible, with enzyme levels returning to 90% of control values 48 h after removal of drug. Although tyrosinase activity is markedly suppressed by yohimbine, the compound has no effect on cell proliferation, cellular translation, or DNA synthesis. Treatment of melanocyte cultures with yohimbine blocks the increase in tyrosinase activity by either 3-isobutyl-1-methylxanthine, dibutyryl cAMP, or forskolin. Results of cAMP immunoassays, show that intracellular levels of the cyclic nucleotide are unaffected in cells treated with yohimbine. Tyrosinase inhibition by yohimbine does not involve a decrease in substrate availability since tyrosine uptake studies show that yohimbine has no effect on the amount of tyrosine entering the cell. Incubation of a melanosome-enriched fraction with yohimbine does not cause a lowering of tyrosinase activity, suggesting that an intact cell is required for yohimbine action. In addition, tyrosinase extracts show no reduction in activity when incubated directly with yohimbine, indicating that the drug does not act as a direct inhibitor of the enzyme. Finally, results of western immunoblotting show that yohimbine does not significantly lower the amount of tyrosinase protein in human melanocytes. These findings suggest that yohimbine acts through an as yet unidentified signaling pathway to lower the catalytic activity of pre-existing tyrosinase molecules present in melanocytes.

Unexpected localization of the Na+/Cl--dependent-like orphan transporter, Rxt1, on synaptic vesicles in the rat central nervous system

Numerous features of its primary structure demonstrate that the orphan transporter Rxt1 belongs to the Na+/Cl--dependent neurotransmitter plasma membrane transporter superfamily, which includes the dopamine, norepinephrine, serotonin and gamma-aminobutyric acid (GABA) transporters. Initial immunocytochemical investigations with affinity-purified antibodies have established that Rxt1 is localized, almost exclusively, in axon terminals of glutamatergic neurons and subsets of GABAergic neurons in the CNS. Further studies were carried out to determine its subcellular distribution. In a first series of experiments, PC-12 cells were transfected with plasmids encoding either the dopamine transporter or Rxt1. Immunofluorescence experiments showed that the dopamine transporter was expressed in these cells, and, as expected, addressed to their plasma membrane. Surprisingly, this was never the case with Rxt1, which was targeted to the same subcellular compartment as synaptophysin, a vesicular protein. In a second set of experiments, subcellular fractionation of rat striatum showed that Rxt1, but not the dopamine transporter, was relatively abundant in the purified synaptic vesicle fraction. Finally, electron microscopic immunocytochemistry with anti-Rxt1 antibodies showed peroxidase as well as pre- and post-embedding immunogold labelling confined to the intracellular compartment in various brain regions. Moreover, quantitative analysis of post-embedding experiments demonstrated that the immunogold particles corresponding to Rxt1 immunoreactivity were mostly localized to small synaptic vesicles. These data indicate that, in contrast with the other members of the Na+/Cl--dependent neurotransmitter transporter superfamily, which are targeted to the plasma membrane, Rxt1 is distributed as a vesicular protein in the CNS.