A comparison of four serological assays for detecting anti-SARS-CoV-2 antibodies in human serum samples from different populations.

It is of paramount importance to evaluate the prevalence of both asymptomatic and symptomatic cases of SARS-CoV-2 infection and their differing antibody response profiles. Here, we performed a pilot study of four serological assays to assess the amounts of anti-SARS-CoV-2 antibodies in serum samples obtained from 491 healthy individuals before the SARS-CoV-2 pandemic, 51 individuals hospitalized with COVID-19, 209 suspected cases of COVID-19 with mild symptoms, and 200 healthy blood donors. We used two ELISA assays that recognized the full-length nucleoprotein (N) or trimeric spike (S) protein ectodomain of SARS-CoV-2. In addition, we developed the S-Flow assay that recognized the S protein expressed at the cell surface using flow cytometry, and the luciferase immunoprecipitation system (LIPS) assay that recognized diverse SARS-CoV-2 antigens including the S1 domain and the carboxyl-terminal domain of N by immunoprecipitation. We obtained similar results with the four serological assays. Differences in sensitivity were attributed to the technique and the antigen used. High anti-SARS-CoV-2 antibody titers were associated with neutralization activity, which was assessed using infectious SARS-CoV-2 or lentiviral-S pseudotype virus. In hospitalized patients with COVID-19, seroconversion and virus neutralization occurred between 5 and 14 days after symptom onset, confirming previous studies. Seropositivity was detected in 32% of mildly symptomatic individuals within 15 days of symptom onset and in 3% of healthy blood donors. The four antibody assays that we used enabled a broad evaluation of SARS-CoV-2 seroprevalence and antibody profiling in different subpopulations within one region.

Plasmacytoid dendritic cells initiate a complex chemokine and cytokine network and are a viable drug target in chronic HCV patients.

Plasmacytoid dendritic cells (pDCs) are the professional type I interferon (IFN)-producing cells, and upon activation they traffic to lymph organs, where they bridge innate and adaptive immunity. Using multianalyte profiling (MAP), we have mapped the key chemokines and cytokines produced in response to pDC activation, taking into consideration the role of autocrine IFN, as well as paracrine effects on other innate cells (e.g., monocytes and conventional DCs). Interestingly, we identify four distinct cytokine/chemokine loops initiated by Toll-like receptor engagement. Finally, we applied this analytic approach to the study of pDC activity in chronic hepatitis C patients. Based on the activation state of pDCs in fresh blood, the lack of agonistic activity of infectious virions, the production of a broad array of cytokines/chemokines once stimulated, and the direct effects of pDCs on other PBMCs, we conclude that the pDCs from hepatitis C virus (HCV)-infected individuals are fully functional and are, indeed, a viable drug target. In sum, this study provides insight into the use of MAP technology for characterizing cytokine networks, and highlights how a rare cell type integrates the activation of other inflammatory cells. Furthermore, this work will help evaluate the therapeutic application of pDC agonists in diseases such as chronic HCV infection.

Vasopressin-V2 receptor stimulation reduces sodium excretion in healthy humans.

In addition to its effect on water permeability, vasopressin, through its V2 receptors (AVPR2), stimulates Na reabsorption in the collecting duct by increasing the activity of the amiloride-sensitive sodium channel ENaC. This study evaluated whether dDAVP (a potent AVPR2 agonist) reduces sodium excretion in healthy humans (n = 6) and in patients with central (C; n = 2) or nephrogenic (N) diabetes insipidus (DI) as a result of mutations of either the aquaporin 2 gene (AQP2; n = 3) or AVPR2 (n = 10). dDAVP was infused intravenously (0.3 microg/kg body wt in 20 min), and urine was collected for 60 min before (basal) and 150 min after the infusion. dDAVP markedly reduced both urine flow rate and sodium excretion in healthy individuals. A reduction in sodium excretion was also observed in CDI and NDI-AQP2 patients but not in NDI-AVPR2 patients. The magnitude of the fall in sodium excretion correlated with the rise in urine osmolality and the fall in urine output but not with the simultaneously observed fall in mean BP. These results suggest that the dDAVP-induced antinatriuresis is due to a direct V2 receptor-dependent stimulation of sodium reabsorption in the collecting duct and is not secondary to a hemodynamic effect. In conclusion, this study reveals a potent V2-dependent antinatriuretic effect of vasopressin in humans. The possibility that an inappropriate stimulation of ENaC by vasopressin might lead to significant sodium retention in chronic situations remains to be determined.

Chronic V2 vasopressin receptor stimulation increases basal blood pressure and exacerbates deoxycorticosterone acetate-salt hypertension.

The present study was intended to determine whether the long-term V2 receptor-mediated effects of vasopressin on sodium reabsorption in the renal collecting duct is an aggravating factor in salt-sensitive hypertension. Deoxycorticosterone acetate (DOCA)-salt hypertension was induced in uninephrectomized rats that had been chronically pretreated with a V2 agonist (dDAVP; 1-deamino-8D-arginine vasopressin; 0.6 microg/kg.d) or a V2 antagonist (SR121463, 3 mg/kg.d) or were untreated. Plasma osmolality and natremia were not significantly different in the groups. Blood pressure was significantly increased by dDAVP pretreatment (+11 mm Hg; P = 0.006), and this effect was exacerbated after DOCA-salt-induced hypertension (+17 mm Hg; P = 0.042). The dDAVP-treated rats had a lower hematocrit (40 +/- 2% vs. 47 +/- 1% and 45 +/- 2%) and markedly higher albuminuria (91 +/- 9 vs. 17 +/- 8 and 15 +/- 8 mg/d), mortality rate (50% vs. 0% and 0%), and cardiac and renal hypertrophy than the control and SR121463 groups. Histological renal lesions were worsened by V2 agonism and prevented by V2 antagonism. Renal mRNA expression of beta- and gamma-subunits of the epithelial sodium channel was significantly increased by dDAVP treatment (P < 0.05). These findings provide evidence that chronic stimulation of vasopressin V2 receptor raises basal blood pressure in rats and exacerbates the development of DOCA-salt hypertension, organ damage, and mortality. These effects could be due at least in part to the sustained stimulation of sodium reabsorption by epithelial sodium channel in the distal part of the nephron, which promotes sodium retention.