DYNAMICS OF ANTIBODIES TO VARIOUS ANTIGENS OF THE SARS-COV-2 CORONAVIRUS IN PATIENTS WITH CONFIRMED COVID-19 INFECTION

Presence of IgG and IgM antibodies in venous blood of 76 patients with confirmed presence of SARS-CoV-2 was determined. The study was carried out by ELISA using Russian test systems. Revealed different levels of IgM antibodies to N-protein and RBD (receptor binding domain of the Spike protein). The level of IgM to RBD did not reach high values, while the level of IgM to N-protein sharply increased in a short period of time to high values by the 3rd week of the disease and decreased only by the 8th week. The dynamics of IgG antibodies to the whole virion antigen and the recombinant spikes was similar, reaching high values at 4-5 weeks of the disease, however, the dynamics of IgG to the N-protein differed, showing a slight increase by the 1st week of the disease and a low level throughout the entire period of observation. Different dynamics of production of IgG and IgM antibodies to N-protein and RBD were noted. The amount of IgM to the N-protein increased sharply and reached a high level, while the amount of IgG increased smoothly and did not show a high level. The opposite picture was observed for antibodies to RBD. The characteristic dynamics of IgG, measured using test systems withsorbed whole virion or recombinant spike proteins, suggests duration of the disease

Heavily Isotype-Dependent Protective Activities of Human Antibodies against Vaccinia Virus Extracellular Virion Antigen B5

ABSTRACT Antibodies against the extracellular virion (EV or EEV) form of vaccinia virus are an important component of protective immunity in animal models and likely contribute to the protection of immunized humans against poxviruses. Using fully human monoclonal antibodies (MAbs), we now have shown that the protective attributes of the human anti-B5 antibody response to the smallpox vaccine (vaccinia virus) are heavily dependent on effector functions. By switching Fc domains of a single MAb, we have definitively shown that neutralization in vitro—and protection in vivo in a mouse model—by the human anti-B5 immunoglobulin G MAbs is isotype dependent, thereby demonstrating that efficient protection by these antibodies is not simply dependent on binding an appropriate vaccinia virion antigen with high affinity but in fact requires antibody effector function. The complement components C3 and C1q, but not C5, were required for neutralization. We also have demonstrated that human MAbs against B5 can potently direct complement-dependent cytotoxicity of vaccinia virus-infected cells. Each of these results was then extended to the polyclonal human antibody response to the smallpox vaccine. A model is proposed to explain the mechanism of EV neutralization. Altogether these findings enhance our understanding of the central protective activities of smallpox vaccine-elicited antibodies in immunized humans.

Molecular Fine-Specificity Analysis of Antibody Responses to Human Cytomegalovirus and Design of Novel Synthetic-Peptide-Based Serodiagnostic Assays

To identify single immunodominant marker proteins which can replace complex virion antigen in serodiagnostic assays, we investigated in detail the molecular fine specificity of antibody responses in different individuals with latent or active human cytomegalovirus (HCMV) infection. An overview of the HCMV proteins recognized by human antibodies was obtained by immunoblotting. For selected immunodominant proteins the epitope fine specificity of the antibody response was determined by a peptide-scanning enzyme-linked immunosorbent assay (ELISA). Epitope clusters were synthesized as combination peptides and were used for further serologic analysis of immunoglobulin M (IgM) and IgG reactivities with panels of sera from different groups of patients in comparison to those with cytomegalovirus (CMV) virion antigen. Several serum samples had significantly higher reactivities with peptides than with the CMV virion antigen. However, individual serum samples occasionally recognized diverse peptide epitopes, stressing the importance of using combinations of peptides in serologic assays. From these studies we were able to define a specific combination of peptides derived from pp52 (UL44) and pp150 (UL32) for the specific and highly sensitive early detection of HCMV IgM, whereas a combination of peptides from pp150 (UL32), gB (UL55), and pp28 (UL99) was selected to give optimal and specific reactivity with HCMV IgG. On the basis of the results obtained with these peptide combinations, new, highly specific serodiagnostic assays were constructed. These assays had sensitivities of 98.9 and 96.4% for IgG and IgM, respectively, in comparison with the results obtained with the “gold standard,” the virion antigen-based ELISA. From the results of this study we conclude that specific combinations of highly defined synthetic peptides can replace complex HCMV virion extracts used in current serodiagnostics and may add to further standardization of HCMV serology.

Joint recognition by cytotoxic T cells of inactivated Sendai virus and products of the major histocompatibility complex.

Cytotoxic T cells specific for Sendai virus were generated by culturing murine spleen cells in vitro together with UV-inactivated Sendai virus. In vivo immunization of donor mice with UV-inactivated Sendai virus resulted in an in vitro secondary response of increased magnitude. Cytotoxic activity was demonstrated in a short-term 51Cr-release assay, using syngeneic tumor cells which had been coated with inactivated Sendai virus by incubation at 4 degrees C for 30 min. The lysis of Sendai virus-coated target cells was restricted by the H-2 haplotype of the target cells, suggesting that the H-2 genes of the target cell contributed to the specificity of the lysis. Kinetic experiments showed that susceptibility to lysis by cytotoxic T cells specific for Sendai virus appeared within 30 min after coating target cells with inactivated virus. Furthermore, there was no detectable synthesis of new proteins in cells treated with UV-inactivated Sendai virus. For these reasons, we suggest that neither viral replication nor the synthesis of new proteins are necessary for the production of the antigen recognized by cytotoxic cells specific for Sendai virus. We infer that the virus-specific component on the target cells is probably a preformed virion antigen adsorbed onto or integrated into the cell membrane. These results imply that, if the cytotoxic T cell recognizes a single antigenic determinant specified both by viral and H-2 genes, this determinant is formed by the physical association of H-2 and Sendai virus antigens rather than by their alteration during the processes of synthesis.