Biological and Clinical Factors contributing to the Metabolic Heterogeneity of Hospitalized Patients with and without COVID-19

The Corona Virus Disease 2019 (COVID-19) pandemic represents an ongoing worldwide challenge. Exploratory studies evaluating the impact of COVID-19 infection on the plasma metabolome have been performed, often with small numbers of patients, and with or without relevant control data; however, determining the impact of biological and clinical variables remains critical to understanding potential markers of disease severity and progression. The present large study, including relevant controls, sought to understand independent and overlapping metabolic features of samples from acutely ill patients (n = 831), testing positive (n = 543) or negative (n = 288) for COVID-19. High-throughput metabolomics analyses were complemented with antigen and enzymatic activity assays on 831 plasma samples from acutely ill patients while in the emergency department, at admission, and during hospitalization. We then performed additional lipidomics analyses of the 60 subjects with the lowest and highest body mass index, either COVID-19 positive or negative. Omics data were correlated to detailed data on patient characteristics and clinical laboratory assays measuring coagulation, hematology and chemistry analytes. Significant changes in arginine/proline/citrulline, tryptophan/indole/kynurenine, fatty acid and acyl-carnitine metabolism emerged as highly relevant markers of disease severity, progression and prognosis as a function of biological and clinical variables in these patients. Further, machine learning models were trained by entering all metabolomics and clinical data from half of the COVID-19 patient cohort and then tested on the other half yielding ~ 78% prediction accuracy. Finally, the extensive amount of information accumulated in this large, prospective, observational study provides a foundation for follow-up mechanistic studies and data sharing opportunities, which will advance our understanding of the characteristics of the plasma metabolism in COVID-19 and other acute critical illnesses.

Affinity of human IgG subclasses to mouse Fc gamma receptors

Human IgG is the main antibody class used in antibody therapies because of its efficacy and longer half-life, which are completely or partly due to FcγR-mediated functions of the molecules. Preclinical testing in mouse models are frequently performed using human IgG, but no detailed information on binding of human IgG to mouse FcγRs is available. The orthologous mouse and human FcγRs share roughly 60-70% identity, suggesting some incompatibility. Here, we report binding affinities of all mouse and human IgG subclasses to mouse FcγR. Human IgGs bound to mouse FcγR with remarkably similar binding strengths as we know from binding to human ortholog receptors, with relative affinities IgG3>IgG1>IgG4>IgG2 and FcγRI>>FcγRIV>FcγRIII>FcγRIIb. This suggests human IgG subclasses to have similar relative FcγR-mediated biological activities in mice.

Prevention of transfusion-transmitted cytomegalovirus in low-birth weight infants (≤1500 g) using cytomegalovirus-seronegative and leukoreduced transfusions

The transfusion-transmitted cytomegalovirus (TT-CMV) can cause serious morbidity and mortality in low-birth weight infants (LBWIs). Transfusion-transmitted cytomegalovirus can be minimized in LBWIs born to cytomegalovirus (CMV)-seronegative mothers with the use of CMV-seronegative blood components. Despite evidence that has independently shown that either leukoreduction or the use of CMV-seronegative components mitigates TT-CMV, the potential efficacy of combining these 2 strategies has not been substantiated in very LBWIs (<1500 g) born to either CMV-seronegative or CMV-seropositive mothers. Nonetheless, the serious risks of CMV infection posed by allogeneic transfusions and the broad implementation of universal leukoreduction have made this combination strategy the de facto clinical standard for transfusion of LBWIs. Although preferred, this combined approach has not been validated in clinical trials and, thus, warrants a large prospective study to determine whether this is the optimal transfusion tactic or if additional safety measures are necessary to prevent TT-CMV in LBWIs born to both CMV- seronegative and CMV-seropositive mothers. The aim of this prospective birth cohort study, therefore, is to estimate the incidence of TT-CMV in 1300 LBWIs (≤1500 g) who receive CMV-seronegative plus leuko-reduced blood products to evaluate the effectiveness of this coupled strategy. Conducted in Atlanta, GA, this study has been registered at the US National Institutes of Health (ClinicalTrials.gov no. NCT00907686).

Inability of Monoclonal Antibodies to Clear Red Blood Cells during Incompatible Transfusions is not a Property of the Whole Cell (84.19)

During an incompatible transfusion (Tx), antibodies (Abs) against some blood group antigens (Ags) will lead to hemolysis while others will allow for continued red blood cell (RBC) circulation despite IgG binding. We tested the nature of RBC clearance using transgenic mice expressing well-defined RBC Ags and monoclonal Abs. Tx of RBCs, expressing human glycophorin A (hGPA), into mice treated with anti-hGPA IgG1 monoclonal Abs led to partial clearance of those RBCs. A population of RBCs persisted and continued to circulate in a 2nd animal also passively immunized against hGPA, indicating that survival was not due to splenic saturation or consumption of the monoclonal Abs. We therefore concluded that these hGPA RBCs were resistant to clearance as they were also positive for hGPA and bound Abs. These studies were also performed using RBCs expressing the Duffy Ag and anti-Duffy IgG2a monoclonal Abs. To test if resistance comprises a whole cell protection from Ab-induced lysis, we transfused blood expressing both hGPA and Duffy Ags into mice passively immunized against hGPA. The resistant RBCs were then transfused into mice passively immunized against Duffy. Although these RBCs were able to resist a 2nd Tx against the same anti-hGPA Ab as the one used during the 1st Tx, these did not resist a 2nd Tx during which anti-Duffy was used. We, therefore, conclude that resistance occurs with different Ags and is not a property of the cell but rather is at the Ag-Ab level.

Inhibition of the primary antibody response to transfused allogeneic platelets (145.8)

Alloantibodies are a clinically significant sequela of platelet (PLT) transfusion, potentially rendering patients refractory to ongoing transfusion support. PLTs are restricted to the peripheral circulation, where antigens are primarily sampled by the spleen and liver. We hypothesized that the primary antibody (Ab) response to allogeneic PLTs depends upon CD4 T cell help in the splenic microenvironment. C57BL/6 recipients (H-2b) transfused four times weekly with 1x108 leukoreduced BALB/c (H-2d) PLTs developed anti-donor Ab by day 28 (15/15 mice). Adoptive transfer of CFSE labeled CD4+ TCR75 cells, a TCR transgenic specific for a peptide from Kd presented by I-Ab, augmented the Ab response by day 14 to a single transfusion (9/9). TCR75 division by day 5 was exclusive to the spleen and not the liver or lymph nodes. Anti-donor Ab was undetectable in CD4 depleted recipients (0/15). Splenectomized recipients did not develop detectable anti-donor Ab (0/13) and adoptively transferred TCR75 cells did not divide or rescue the Ab response (0/9). The non-responsiveness in splenectomized animals was not due to donor specific tolerance as these recipients responded robustly to subsequent donor whole blood (6/6). Enhanced alloimmunization by adoptive transfer and abrogation by depletion supports the critical role for CD4 T cell help. Failure of TCR75 proliferation in splenectomized recipients suggests that an intact spleen is required, but the liver insufficient, for PLT alloimmunization.

Activation of the double-stranded-RNA-activated protein kinase and induction of vascular cell adhesion molecule-1 by poly (I).poly (C) in endothelial cells

Double-stranded RNA (dsRNA) induces the vascular cell adhesion molecule VCAM-1 to high levels of expression in human umbilical vein endothelial (HUVE) cells. Although VCAM-1 is also induced by the cytokine interleukin 1 beta (IL-1 beta), activation of the dsRNA-activated protein kinase (PKR) occurs only in response to incubation with dsRNA but not with IL-1 beta. Incubation of HUVE cells with the synthetic dsRNA, poly (I).poly (C), activates PKR with increased autophosphorylation, increased phosphorylation of the translation factor eIF2 alpha, and increased activation of the transcription factor NF-kappa B. Promoter analysis in HUVE cells using a VCAM-1 promoter linked to CAT reporter gene demonstrates that poly (I).poly (C) responsiveness resides in the minimal VCAM-1 promoter that contains two NF-kappa B sites, and deletion of the NF-kappa B sites eliminates basal and poly (I).poly (C)-induced CAT activity, supporting the importance of NF-kappa B in the poly (I).poly (C)-mediated induction of VCAM-1. In vitro studies using purified reagents demonstrate that PKR is capable of phosphorylating I kappa B alpha (the inhibitory subunit of NF-kappa B) in a dsRNA-dependent manner. This suggests that phosphorylation of I kappa B alpha by PKR could be an initial step in the activation of NF-kappa B by dsRNA. NF-kappa B is also activated by IL-1 beta in HUVE cells, but this activation occurs without increased PKR autophosphorylation or eIF2 alpha phosphorylation. Poly (I).poly (C) induces VCAM-1 mRNA levels that are dramatically higher and sustained longer than levels induced by IL-1 beta. Although phosphorylation of eIF2 alpha interferes with protein translation, sufficient VCAM-1 mRNA translation occurs in response to poly (I).poly (C) to yield VCAM-1 protein levels that are similar to levels that are induced by IL-1 beta. This suggests that the higher, sustained VCAM-1 mRNA levels that occur in response to incubation with poly (I).poly (C) compensate for the partial translational block resulting from increased eIF2 alpha phosphorylation. These studies indicate that transcriptional and translational regulatory events that occur in response to activation of PKR by dsRNA are important in the regulation of VCAM-1 gene expression in HUVE cells.