The sensitivity of SARS-CoV-2 antigen tests in the view of large-scale testing.

OBJECTIVES: Antigen tests have emerged as an alternative to SARS-CoV-2 diagnostic PCR, thought to be valuable especially for the screening of bigger communities. To check appropriateness of the antigen based testing, we determined sensitivity of two point-of-care antigen tests when applied to a cohort of COVID-19 symptomatic, COVID-19 asymptomatic and healthy persons. METHODS: We examined nasopharyngeal swabs with antigen test 1 (Panbio Covid-19 Ag Rapid Test, Abbott) and antigen test 2 (Standard F Covid-19 Ag FIA, SD Biosensor). An additional nasopharyngeal and oropharyngeal swab of the same individual was checked with PCR (Allplex SARS-nCoV-2, Seegene). Within a 4-day period in October 2020, we collected specimens from 591 subjects. Of them, 290 had COVID-19 associated symptoms. RESULTS: While PCR positivity was detected in 223 cases, antigen test 1 and antigen test 2 were found positive in 148 (sensitivity 0.664, 95%CI 0.599, 0.722) and 141 (sensitivity 0.623, 95%CI 0.558, 0.684) patients, respectively. When only symptomatic patients were analysed, sensitivity increased to 0.738 (95%CI 0.667, 0.799) for the antigen test 1 and to 0.685 (95%CI 0.611, 0.750) for the antigen test 2. The substantial drop in sensitivity to 12.9% (95%CI 0.067, 0.234) was observed for samples with the PCR threshold cycle above > 30. CONCLUSIONS: Low sensitivity of antigen tests leads to the considerable risk of false negativity. It is advisable to implement repeated testing with high enough frequency if the antigen test is used as a frontline screening tool, and to follow with PCR if it is applied to vulnerable populations.

Molecular-orbital study of hydroxylation of collagenous proline and lysine.

EHT and CNDO/2 types of calculations permit the interpretation of the course of hydroxylation of collagenous proline and lysine. Calculations were performed for the models of proline (I), zwitterion of proline (II), proline-containing peptide (III), and lysine (IV). The theoretical results are consistent with an electrophilic mechanism.

Effect of intermittent high altitude hypoxia on the synthesis of collagenous and non-collagenous proteins of the right and left ventricular myocardium.

The incorporation of 14C-proline into collagenous and non-collagenous proteins of the right and left ventricular myocardium was investigated in rats exposed to intermittent high altitude hypoxia. Experimental results have shown that even in control animals significant differences exist in the concentration and synthesis of individual protein fractions between the right and left ventricular myocardium. Long-term exposure to intermittent high altitude hypoxia induced a significantly increased concentration of collagenous and non-collagenous proteins in both ventricles. The incorporation of 14C-proline was not affected at this period (ie period of stabilised hypertrophy) in either of the fractions studied.

The chemiluminescence of rabbit alveolar macrophages induced by quartz dust particles.

Quartz dust particles (respirable fraction) triggered luminol-dependent chemiluminescence (CL) when added to unstimulated rabbit alveolar macrophages (AM). It was shown by increasing the dust dose added to the same amount of cells, and conversely, that the intensity of chemiluminescent reaction depended on the ratio cells:dust particles. The ratio giving maximum CL yield was estimated.

Effects of magnetic field exposure on the development of lung fibrosis elicited by industrial pollutants.

Lung injury elicited by a single intratracheal instillation of fibrogenic (quartz) and nuisance (anatase) dusts and/or weekly repeated instillation of CdCl2 solution combined with sinusoidal (50 Hz, 10 mT) magnetic field (MF) exposure was studied in male rats. Combined effects in bronchoalveolar lavage (BAL), rat lungs and regional lymph nodes after 4 months of MF exposure (1 h/5 days per week) were evaluated biochemically and by cytological and histopathological examination. Damage of cell membranes in the cell part of BAL due to MF exposure was not observed in the examined animal groups. Following MF exposure, decreased synthesis of collagen proteins (incorporation of [14C]proline) was demonstrated in lungs with quartz dust burden. Histological examination revealed differences in the lung tissue reaction suggesting the modification of the repair process due to MF exposure following experimental injury in both quartz and cadmium groups.

Creatinephosphokinase in human diploid cell lines.

The activity of CPK was proved in cultivated cells from amniotic fluid cells, thymus, spleen, pericardium, umbilical cord, skin and muscle. The activity in these strains did not significantly differ. The average value is 224 plus or minus 68 i.u. CPK/mg N. No differences of activity were disclosed between embryonal, foetal and children cultures. The activity of CPK in post mortem cultures was not altered. The relationship between collagen synthesis and CPK activity is suggested. The evidence of CPK activity in amniotic fluid cells corresponding to the activity in other foetal cultures and the whole sample under investigation opens the way to the prenatal investigation of pathophysiology and inborn errors of the metabolism of this enzyme.

Biosynthesis of collagen during the life cycle of human diploid cell lines.

In the course of the active phase of growth collagen synthesis appears relatively stable and decreases when the culture passes into the degenerative phase III. The increase of cell nitrogen indicates the increasing accumulation of cell proteins with their aging in vitro. The ratio of soluble to insoluble collagen is relatively constant in fibroblast cultures from different tissues, periods of development during the active phase of growth. The increase of insoluble collagen in long term cultivated Marfan syndrome fibroblasts indicates the possible relationship between increasing stability of collagen and ageing of fibroblasts in vitro. Further studies confirmed the significant differences between control fibroblast and fibroblast derived from tissues of patients affected by Marfan syndrome. No differences were found in collagen synthesis and in the ratio of soluble to insoluble collagen in fibroblast strains from embryos, foetuses, children and young adults. The collagen synthesis and the ratio of soluble to insoluble collagen does not differ in fibroblast cultures derived from or post-natal period of life. The collagen synthesis in amniotic fluid cells was confirmed by analysis of cell proteins and proteins produced into the cultivation medium. The ultrastructural analysis of these cells reveals formation of intracellular fibrills and their growth in the extracellular space. The possibility of prenatal investigation of inborn errors of collagen metabolism is pointed out.