Elevated Humoral Immune Response to SARS-CoV-2 at High Altitudes Revealed by an Anti-RBD “In-House” ELISA

Abstract

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a global pandemic with dramatic health and socioeconomic consequences. The Coronavirus Disease 2019 (COVID-19) challenges health systems to quickly respond by developing new diagnostic strategies that contribute to identify infected individuals, monitor infections, perform contact-tracing, and limit the spread of the virus. In this brief report, we developed a highly sensitive, specific, and precise “In-House” ELISA to correctly discriminate previously SARS-CoV-2-infected and non-infected individuals and study population seroprevalence. Among 758 individuals evaluated for anti-SARS-CoV-2 serology in the province of Tucumán, Argentina, we found a weak correlation between antibodies elicited against the RBD, the receptor-binding domain of the Spike protein, and the nucleocapsid (N) antigens of this virus. Additionally, we detected mild levels of anti-RBD IgG antibodies in 33.6% of individuals diagnosed with COVID-19, while only 19% showed sufficient antibody titers to be considered as plasma donors. No differences in IgG anti-RBD titers were found between women and men, neither in between different age groups ranging from 18 to 60. Surprisingly, individuals from a high altitude village displayed elevated and longer lasting anti-RBD titers compared to those from a lower altitude city. To our knowledge, this is the first report correlating altitude with increased humoral immune response against SARS-CoV-2 infection.

Evaluation of S- and M-Proteins Expressed in Escherichia coli and HEK Cells for Serological Detection of Antibodies in Response to SARS-CoV-2 Infections and mRNA-Based Vaccinations

“…The sensitivities of the RBD-protein ELISA ranged from 50% in the early stage to 90.8% in late stages of COVID-19, while the M-protein provided lower sensitivities of 33.3% to 41.7% considering IgG antibodies. The sensitivity of the RBD ELISA in group 3 was comparable to previously reported ELISA results using samples collected at least three weeks after diagnosis of SARS-CoV-2 [25,26]. Algaissi et al also reported a sensitivity of 40-60% in the S1 IgG ELISA for earlier time points [16], which relates very well to the current study.…”

“…As E. coli RBD did not provide good results in the IgG-based ELISA, although it bound to the ACE2 receptor, it was not further considered for testing [24]. Thus, RBD was expressed in HEK cells, as previous reports indicated also a good sensitivity in ELISA [16,[25][26][27]. When the monomeric and dimeric versions of RBD expressed in HEK cells in-house and two commercial RBDs were coated in ELISA, the obtained OD 450 -values were identical within the error range (Figure S7).…”

Humoral immunoresponse elicited against an adenoviral-based SARS-CoV-2 coronavirus vaccine in elderly patients

“…The basic demographics of the population studied are shown in Table 1 . Humoral immune responses against the RBD of the SARS-CoV-2 Spike glycoprotein were evaluated at different time points, from 0 to 180 days post vaccination (dpv) by a previously published anti-RBD “ In House ” ELISA [ 18 ].…”

“…Anti-RBD titers of convalescent individuals (CP) acquired with the same ELISA platform were obtained from previous studies [ 17 , 18 ]. This population was defined as individuals diagnosed with both RT-PCR and serology with both anti-RBD IgG ELISA and anti-N CMIA) who provided serum samples 28–42 days-post diagnosis with SARS-CoV-2 infection and with a median age of 36.9 ± 13.6.…”

“…Serum RBD-specific IgG antibody titers were determined by an “ in house ELISA” as previously described [ 17 , 18 ]. Briefly, 0.1 μg of recombinant RBD from SARS-CoV-2 was immobilized in each well of a 96-well flat polystyrene bottom plates (High Binding, Half-Area, Greiner #675,061).…”