[High Heterogeneity of Virus-Neutralizing and RBD-Binding Activities of COVID-19 Convalescent Sera].

The parameters of the humoral response are an important immunological characteristic of donors who recovered from COVID-19 and vaccinated individuals. Analysis of the level of virus-binding antibodies has become widespread. The most accurate predictor of effective immune protection against symptomatic SARS-CoV-2 infection is the activity of virus-neutralizing antibodies. We determined virus-neutralizing activities in plasma samples of individuals (n = 111) who had COVID-19 from April to September 2020. Three independent methods were used: conventional with live virus, with virus-like particles pseudotyped with spike protein, and a surrogate virus-neutralization test (cVNT, pVNT and sVNT, respectively). For comparison, the levels of IgG, IgA and IgM antibodies against the receptor-binding domain of the SARS-CoV-2 spike protein were also evaluated. The levels of virus-binding as well as virus-neutralizing antibodies in cVNT and pVNT showed high heterogeneity. A comparison of cVNT and pVNT results showed a high correlation, sVNT results also correlated well with both cVNt and pVNT. To the greatest extent, the level of IgG antibodies correlated with the results of cVNT, pVNT and sVNT. These results can be used in the selection of plasmas that are best suited for transfusion and treatment of acute COVID-19. In addition, data on the virus-neutralizing activity of plasma are important for the selection of potential donors, for the isolation of SARS-CoV-2-specific B-lymphocytes, in order to further generate monoclonal virus-neutralizing antibodies.

High Heterogeneity of Virus-Neutralizing and RBD-Binding Activities of COVID-19 Convalescent Sera.

The parameters of the humoral response are an important immunological characteristic of donors who recovered from COVID-19 and vaccinated individuals. Analysis of the level of virus-binding antibodies has become widespread. The most accurate predictor of effective immune protection against symptomatic SARS-CoV-2 infection is the activity of virus-neutralizing antibodies. We determined virus-neutralizing activities in plasma samples of individuals (n = 111) who had COVID-19 from April to September 2020. Three independent methods were used: conventional with live virus, with virus-like particles pseudotyped with spike protein, and a surrogate virus-neutralization test (cVNT, pVNT and sVNT, respectively). For comparison, the levels of IgG, IgA and IgM antibodies against the receptor-binding domain of the SARS-CoV-2 spike protein were also evaluated. The levels of virus-binding as well as virus-neutralizing antibodies in cVNT and pVNT showed high heterogeneity. A comparison of cVNT and pVNT results showed a high correlation, sVNT results also correlated well with both cVNT and pVNT. To the greatest extent, the level of IgG antibodies correlated with the results of cVNT, pVNT and sVNT. These results can be used in the selection of plasmas that are best suited for transfusion and treatment of acute COVID-19. In addition, data on the virus-neutralizing activity of plasma are important for the selection of potential donors, for the isolation of SARS-CoV-2-specific B-lymphocytes, in order to further generate monoclonal virus-neutralizing antibodies.

[The perspective fluoroplastic porous carrier for conservation and transfer of samples of blood plasma: application of "dry drop" technique with the purpose of detection of individual fatty acids.]

It is proposed for preserving samples of biological fluids (blood plasma first of all) and mailing them to analytical laboratory to significantly modify a well-known technique of "dried blood spot" (DBS) at the expense of application of home-made fluoroplastic filtering material type MFFK-G as a porous carrier of fluid biological sample. The synthetic material contains no chemically active molecular fragments and it has four times greater water capacity than filter and chromatographic paper. Thus, fluoroplastic porous disc of mass of 15 mg is suitable to carrying of 70-100 mkl (instead of 15-20 mkl) of fluid. The preliminary impregnation of such a disc with solution of antioxidant - 0.5% - 0.9% 2,6-di-tret-butyl-4-methyl phenol in chloroform - permits to strongly increase stability of higher poly-saturated fatty acids in applied of dry plasma sample or erythrocytic mass on the disc. In that case, time of storage of ready-made disc with dry sample under room temperature increases up to 35-40 days and time of storage in freezer - from 50-60 days to half a year and longer. The storage of dry samples in airtight bottles of vials air-blown with technical propanebutane, also increases time of storage of samples approximately on a degree. This method permits to qualitatively determine content of individual fatty acids in the fraction of etherized and non-etherized fatty acids and also total and free cholesterol in samples of biological fluids.