Validation of a combined ELISA to detect IgG, IgA and IgM antibody responses to SARS-CoV-2 in mild or moderate non-hospitalised patients

BACKGROUND

Frequently SARS-CoV-2 results in mild or moderate disease with potentially lower concentrations of antibodies compared to those that are hospitalised. Here, we validated an ELISA using SARS-CoV-2 trimeric spike glycoprotein, with targeted detection of IgG, IgA and IgM (IgGAM) using serum and dried blood spots (DBS) from adults with mild or moderate disease.

METHODS

Targeting the SARS-CoV-2 trimeric spike, a combined anti-IgG, IgA and IgM serology ELISA assay was developed using 62 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 624 COVID-19 negative samples. The assay was validated using 73 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 359 COVID-19 negative serum samples with an additional 81 DBSs. The assay was further validated in 226 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, ≥14 days post symptom onset and 426 COVID-19 negative clinical samples.

RESULTS

A sensitivity and specificity of 98.6% (95% CI, 92.6-100.0), 98.3% (95% CI, 96.4-99.4), respectively, was observed following validation of the SARS-CoV-2 ELISA. No cross-reactivities with endemic coronaviruses or other human viruses were observed, and no change in results were recorded for interfering substances. The assay was stable at temperature extremes and components were stable for 15 days once opened. A matrix comparison showed DBS to correlate with serum results. Clinical validation of the assay reported a sensitivity of 94.7% (95% CI, 90.9-97.2%) and a specificity of 98.4% (95% CI, 96.6-99.3%).

CONCLUSIONS

The human anti-IgGAM SARS-CoV-2 ELISA provides accurate and sensitive detection of SARS-CoV-2 antibodies in non-hospitalised adults with mild or moderate disease. The use of dried blood spots makes the assay accessible to the wider community.

Update on neuromyelitis optica: natural history and management

Neuromyelitis optica or Devic disease is an inflammatory disorder of the central nervous system. It is caused by antibodies that attack aquaporin 4 water channels in the cell membrane of astrocytic foot processes at the blood brain barrier. It can involve the optic nerve, the spinal cord and beyond. Here we review its pathophysiology, clinical features, and therapy.

KCa2 channels activation prevents [Ca2+]i deregulation and reduces neuronal death following glutamate toxicity and cerebral ischemia

Exacerbated activation of glutamate receptor-coupled calcium channels and subsequent increase in intracellular calcium ([Ca2+]i) are established hallmarks of neuronal cell death in acute and chronic neurological diseases. Here we show that pathological [Ca2+]i deregulation occurring after glutamate receptor stimulation is effectively modulated by small conductance calcium-activated potassium (KCa2) channels. We found that neuronal excitotoxicity was associated with a rapid downregulation of KCa2.2 channels within 3 h after the onset of glutamate exposure. Activation of KCa2 channels preserved KCa2 expression and significantly reduced pathological increases in [Ca2+]i providing robust neuroprotection in vitro and in vivo. These data suggest a critical role for KCa2 channels in excitotoxic neuronal cell death and propose their activation as potential therapeutic strategy for the treatment of acute and chronic neurodegenerative disorders.

Gully hotspot contribution to landscape methane (CH4) and carbon dioxide (CO2) fluxes in a northern peatland

Peatlands are long term carbon catchments that sink atmospheric carbon dioxide (CO(2)) and source methane (CH(4)). In the uplands of the United Kingdom ombrotrophic blanket peatlands commonly exist within Calluna vulgaris (L.) dominated moorland ecosystems. These landscapes contain a range of topographical features that influence local hydrology, climate and plant community composition. In this study we examined the variation in ecosystem CO(2) respiration and net CH(4) fluxes from typical plant-soil systems in dendritic drainage gullies and adjacent blanket peat during the growing season. Typically, Eriophorum spp., Sphagnum spp. and mixed grasses occupied gullies while C. vulgaris dominated in adjacent blanket peat. Gross CO(2) respiration was highest in the areas of Eriophorum spp. (650+/-140 mg CO(2) m(-2) h(-1)) compared to those with Sphagnum spp. (338+/-49 mg CO(2) m(-2) h(-1)), mixed grasses (342+/-91 mg CO(2) m(-2) h(-1)) and C. vulgaris (174+/-63 mg CO(2) m(-2) h(-1)). Measurements of the net CH(4) flux showed higher fluxes from the Eriophorum spp (2.2+/-0.6 mg CH(4) m(-2) h(-1)) locations compared to the Sphagnum spp. (0.6+/-0.4 mg CH(4) m(-2) h(-1)), mixed grasses (0.1+/-0.1 mg CH(4) m(-2) h(-1)) and a negligible flux detected from C. vulgaris (0.0+/-0.0 mg CH(4) m(-2) h(-1)) locations. A GIS approach was applied to calculate the contribution of gullies to landscape scale greenhouse gas fluxes. Findings from the Moor House National Nature Reserve in the UK showed that although gullies occupied only 9.3% of the total land surface, gullies accounted for 95.8% and 21.6% of the peatland net CH(4) and CO(2) respiratory fluxes, respectively. The implication of these findings is that the relative contribution of characteristic gully systems need to be considered in estimates of landscape scale peatland greenhouse gas fluxes.

Total serum IgE and IgE antibodies specific to house dust mite found in two aged-matched cohorts of children with and without otitis media with effusion

OBJECTIVES

To determine whether otitis media with effusion (OME) is associated with elevated serum immunoglobulin E (IgE) and IgE specific for house dust mite.

DESIGN

Forty-seven children who had evidence of bilateral OME, both otoscopically and on tympanometry, on two separate occasions, 3 months apart were admitted for ventilation tubes. Forty-eight children admitted for minor eye surgery who had otoscopically normal ears and no history of middle ear problems were used as controls. Bloods samples were taken under anaesthesia. Total IgE and IgE radioallergosorbent test (RAST) to house dust mite was measured by the Pharmacia Unicap 100 system. The results from the two groups were compared.

SETTING

Birmingham Children's Hospital.

PARTICIPANTS

Children between the ages of 3 and 10. Children with Down's syndrome, cleft lip and palate, ciliary abnormalities, known immunodeficiencies and cardiac abnormalities were excluded.

MAIN OUTCOME MEASURES

Total IgE and RAST to house dust mite. A RAST of >0.35 was taken to be positive.

RESULTS

There was no statistical difference between the control and study groups for the total IgE. Six children from both study and control groups had a raised house dust mite RAST. There was no difference in the levels between either group.

CONCLUSIONS

Our findings indicate that there is no direct relationship between OME and biochemical evidence of allergy, specifically to house dust mite.

IgG from myeloperoxidase-antineutrophil cytoplasmic antibody-positive patients stimulates greater activation of primed neutrophils than IgG from proteinase 3-antineutrophil cytosplasmic antibody-positive patients

OBJECTIVE

Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA) have been reported to be pathologically and clinically different. The aim of this study was to assess whether these differences could be explained by differing abilities of proteinase 3-antineutrophil cytoplasmic antibody (PR3-ANCA)-positive IgG preparations or myeloperoxidase-ANCA (MPO-ANCA)-positive IgG preparations to activate neutrophils (polymorphonuclear cells [PMN]) in vitro.

METHODS

Using Percoll density gradients, PMN were isolated (concentration 2 x 10(6)/ml) and primed with cytochalasin B (1 ng/ml) and tumor necrosis factor alpha (TNFalpha; 2 ng/ml). The PMN were activated with 200 microg/ml of normal IgG or ANCA. Activation was determined by 1) superoxide anion generation as determined by the superoxide dismutase-inhibitable reduction of ferricytochrome c, 2) monitoring fluxes in Ca2+ concentration using Fura 2-AM-loaded PMN, and 3) degranulation using an MPO assay. Surface expression of PR3 and MPO was determined by fluorescence-activated cell sorter analysis. ANCA isotypes were investigated by enzyme-linked immunosorbent assay.

RESULTS

Activation of PMN by MPO-ANCA-positive IgG preparations compared with PR3-ANCA-positive IgG preparations resulted in greater generation of superoxide anions (MPO-ANCA-positive IgG preparations 9.13 +/- 0.39 nmoles [mean +/- SEM], PR3-ANCA-positive IgG preparations 6.32 +/- 0.35 nmoles; P < 0.001), Ca2+ fluxes (MPO-ANCA-positive IgG preparations 0.735 +/- 0.10, PR3-ANCA-positive IgG preparations 0.33 +/- 0.098; P < 0.01), and MPO degranulation (MPO-ANCA-positive IgG preparations 251.98 +/- 26.7 ng, PR3-ANCA-positive IgG preparations 145.19 +/- 19.4 ng; P < 0.001). The increased activation seen with MPO-ANCA-positive IgG preparations was not due to increased expression of MPO on the cell surface, because following TNFalpha priming PR3 was expressed on significantly more cells than was MPO (PR3 expression 54.2 +/- 5.18%, MPO 31.6 +/- 3.55%; P < 0.001). IgG1 and IgG4 were the predominant isotypes in both MPO-ANCA-positive IgG preparations and PR3-ANCA. MPO-ANCA contained significantly more IgG1 than did PR3-ANCA, and PR3-ANCA-positive IgG preparations contained significantly more IgG3.

CONCLUSION

In vitro MPO-ANCA-positive IgG preparations are more activating than PR3-ANCA-positive IgG preparations. The increased activation cannot be explained by increased MPO expression on the cell surface or greater IgG3 present in MPO-ANCA-positive IgG preparations. Differences in activation of PMN by these antibodies may determine some differences between WG and MPA.

Molecular determinants of NMDA receptor function in GABAergic neurones of rat forebrain

1. The functional and molecular properties of NMDA receptors (NMDA-Rs) were studied in single, visually identified GABAergic medial septal neurones of the rat forebrain using patch clamp, fluorometric Ca2+ measurements and the single-cell reverse transcription-polymerase chain reaction (RT-PCR) technique. 2. Large neurones close to the mid-line of the medial septal region were shown by the expression of mRNA for a form of glutamate decarboxylase (GAD65) to be almost exclusively GABAergic. A variety of NR2 subunit combinations were detected in the same population of neurones. When tested for NR2A-C, all but one neurone were shown to express mRNA for NR2B. The NR2B subunit mRNA was usually detected together with NR2A or NR2C. mRNA for NR2D was detected in most neurones from a separate batch of cells tested only for this subunit. 3. Single channel measurements in outside-out patches combined with RT-PCR on the same cell showed that NMDA-R channels from these neurones had main single channel conductance levels of 42 pS in 2 mM Ca2+ and 49 pS in 1 mM Ca2+. In addition, a number of other conductance levels were observed, with values in 2 mM Ca2+ of 51, 31, 19 and 13 pS. No clear difference was observed in the pattern of conductance levels displayed by neurones in which different subunit combinations were detected. 4. Whole-cell agonist-induced currents were strongly reduced by the NMDA-R antagonist ifenprodil, at a concentration that mainly affects receptors containing NR2B in recombinant systems. Currents activated by NMDA had a high sensitivity to extracellular Mg2+. 5. The fraction of the total cation current through NMDA-R that was carried by Ca2+, measured using a combination of patch clamp and fluorometry in neurones loaded with a high concentration of the Ca2+ indicator fura-2, was found to be approximately 12%. 6. NMDA-R-mediated excitatory synaptic currents (EPSCs) had similar time courses to those in neurones in other brain regions. The decay kinetics were biexponential, with respective mean values for the fast (tau f) and slow (tau 8) time constants of 79 and 300 ms at -60 mV, and 66 and 284 ms at +40 mV. EPSCs were greatly reduced by ifenprodil (3 microM). 7. In conclusion, NMDA receptors in GABAergic medial septal neurones display a characteristic functional profile. The NR2 subunit mRNA detected and the single channel conductance levels observed suggest that, in addition to NR2B, which is present in nearly all cells, NR2A, NR2C and NR2D are also expressed. However, most of the functional properties of NMDA-Rs in these neurones, including the strong inhibition by ifenprodil and Mg2+, the high fractional Ca2+ current, and the time course of the synaptic currents, are more consistent with those known for NR2B than for the other NR2 subunits. These results suggest that the NR2B subunit dominates over other NR2 subunits in determining the functional properties of NMDA-Rs in these neurones.

Localized calcium signalling and neuronal integration in cerebellar Purkinje neurones

The use of high resolution imaging techniques has revealed new forms of dendritic signal integration in neurones. In contrast to electrical signals that have a more widespread influence on the cell, brief Ca2+ transients resulting from synaptic activation are often restricted to a small part of the dendritic tree. In cerebellar Purkinje neurones, different levels of Ca2+ signalling have been observed that may involve the entire neurone or be spatially limited to fine dendritic structures. The Ca2+ signals accompanying subthreshold excitatory postsynaptic potentials resulting from stimulation of the excitatory parallel fibre input can be restricted to regions as small as a spiny dendrite or a single dendritic spine. With the recruitment of increasing numbers of inputs there is a summation of Ca2+ signals in highly restricted regions of the spiny dendrites that is independent of electrical summation at the soma. Of a number of potential sources that could provide the Ca2+ responsible for the postsynaptic changes, Ca2+ entry through voltage-gated Ca2+ channels has received the most support, although other sources like Ca2+ entry through ligand-gated channels and especially Ca2+ release from intracellular stores need to be considered.

Fractional calcium current through neuronal AMPA-receptor channels with a low calcium permeability

The Ca(2+)-permeation properties of AMPA-receptor (AMPA-R) channels in Purkinje neurons in rat cerebellar slices were studied using a combination of whole-cell patch-clamp recordings, Fura-2 fluorometry, and single-cell reverse-transcription (RT)-PCR. Several lines of evidence indicate that Purkinje neurons, at both early and late stages of postnatal development, express exclusively AMPA-R channels with a low Ca2+ permeability. First, no Ca2+ signal was detected during application of either AMPA or kainate to Purkinje neurons loaded with the Ca2+ indicator Fura-2 AM. In contrast, kainate application induced large Ca2+ transients in Bergmann glia cells. Second, in ion substitution experiments, when Ca2+ is the only extracellular permeant cation, the reversal potential corresponds to that expected for AMPA-R channels with a low permeability for Ca2+. Third, using a fluorometric flux-measurement approach (Schneggenburger et al., 1993a), we found that the Ca2+ fraction of the total cation current through AMPA-R channels is approximately 0.6%. This value is approximately sixfold lower than that found for recombinant AMPA-R lacking the AMPA-R subunit GluR2. Furthermore, single-cell RT-PCR experiments revealed the presence of the AMPA-R subunits GluR1, GluR2, and GluR3 in Purkinje neurons in cerebellar slices at developmental stages corresponding to those studied electrophysiologically. The expression of GluR2 in all cells tested (n = 14) is consistent with the subunit composition predicted from studies of recombinant AMPA-R channels with a low permeability for Ca2+ (Burnashev et al., 1992b). In conclusion, this study establishes that cerebellar Purkinje neurons at all postnatal developmental stages possess AMPA-R channels with a low permeability for Ca2+.

Stereoencephalotomy and control of skeletal muscle tone

Stereotactic interventions at the thalamic or subtalamic level for treatment of pathological hyperkinesias provide a good model for investigation of the systems controlling tonic innervation in the alert subject. It is suggested that the poststereotactic muscular hypotonia observed contralaterally to the lesion is due to changes in the tonic innervation pattern caused by interruption of a proprioceptive feedback loop.

Vibration-evoked reciprocal inhibition between human wrist muscles

Reciprocal inhibition of the voluntarily contracting wrist extensor (extensor carpi radialis, ECR) evoked by proprioceptive afferent input from the flexor (flexor carpi radialis, FCR), was studied in healthy human subjects. Vibration of the FCR tendon was used to elicit Ia-dominated afferent discharge whilst inhibition of ECR was assessed as the reduction in asynchronous, on-going EMG. A small early phase of inhibition (I1) was evident in 25% of trials. The latency (ca. 25 ms) of this component suggested that it was mediated by an Ia oligosynaptic. possibly 'classical' disynaptic, inhibitory pathway. A later and apparently separate phase of reduced activity (I2, ca. 40 ms) was, however, far more consistently observed (96% of trials) and of greater magnitude. The I2 component was usually followed, some 20 ms later, by a phase of elevated activity (E1, 72% trials). Reductions in simultaneously recorded net extensor torque commenced at about 60 ms following the onset of flexor tendon vibration, i.e. some 20 ms after the main I2 EMG component. These mechanical responses must have almost exclusively resulted from reciprocal inhibition of extensor EMG since vibration of the relaxed FCR evoked minimal excitatory flexor activity. The reflex pattern, in any individual subject, was relatively unaffected by altering the duration of the vibration train between one and nineteen cycles (125 Hz). This suggests that the entire response complex resulted largely from the initial afferent volley. The sizes of both the I1 and I2 reductions in ECR activity increased with increasing voluntary extensor contraction so that their depths remained constant proportions of background EMG. Very similar results were obtained when reciprocal inhibition of FCR was produced by vibration of the belly of ECR. Thus, reciprocal inhibition between wrist muscles is mainly expressed as a rather stereotyped, short duration reduction in EMG whose depth is determined by the pre-existing level of motor activity. Some functional implications of this form of reflex behaviour are discussed.

Electromyographic reflexes evoked in human wrist flexors by tendon extension and by displacement of the wrist joint

1. The electromyographic (EMG) reflexes evoked in the wrist flexor muscle, flexor carpi radialis (FCR), by percutaneous extension of its tendon and by forcible extension of the wrist joint have been studied. Reflexes were elicited during steadily maintained voluntary flexor contraction of 10% of each subject's maximum. 2. Tendon extension, using 'ramp and hold' displacements, evoked fairly prolonged (ca 50 ms) increases in EMG activity. These responses were usually subdivided into two main excitatory peaks of respectively short (SL, ca 20 ms) and long (LL, ca 45 ms) latency. This pattern contrasted with that observed following brief tendon taps when only a single, SL peak was elicited. 3. 'Stretch' reflexes evoked by 'ramp and hold' wrist extensions, as has been noted by numerous earlier investigators, were also protracted and comprised two main excitatory components. These responses resembled those produced by tendon extension both in their general form and in their behaviour upon altering the velocity of mechanical stimuli. Quantitatively, however, two main differences were evident. The reflexes evoked by wrist extension, including their SL and LL peaks, were generally somewhat larger. Additionally, when parameters of the two modes of stimulation were adjusted to elicit SL responses of equivalent amplitude, the LL responses elicited by tendon extension were regularly smaller and of shorter duration than those elicited by wrist extension. 4. Termination of the two forms of mechanical stimulation, by releasing tendon or wrist extension, each elicited a SL reduction in EMG activity. Such troughs were more pronounced and more consistently observed upon release of wrist extension. 5. Neither local anaesthesia of the skin overlying the flexor tendons at the wrist nor ischaemia of the hand and lower forearm produced any systematic modification of reflex response patterns. 6. It is concluded that intramuscular receptors (presumably muscle spindles) in FCR mediate both the SL and LL reflexes evoked in this muscle by extension of its tendon. Intramuscular receptors also seem certain to be very largely responsible for the EMG responses generated in this muscle by wrist extension.