Introduction
The coronavirus disease-19 (COVID-19) is caused by a virus called severe
acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (Zhou, Yang et al.
2020). The virus is a single-stranded RNA virus coding for major
structural surface glycoproteins: spike (S), matrix (M), envelope (E),
and nucleoprotein (N) and a set of 16 nonstructural proteins (NSPs) as
well as several additional open reading frames encoding for accessory
proteins involved in host-virus interactions (Bartlam, Yang et al.
2005). The S protein is a homotrimeric protein consisting of the
functional domains S1 and S2 which are responsible for binding of the
virus to the angiotensin converting enzyme-2 (ACE2) (Shang, Ye et al.
2020). Spread of the virus is done by person to person contact via
airborne droplets and aerosols. Most of the infected persons develop
mildly symptomatic disease such as fever, cough, dyspnea, fatigue
headache, dysgusia, anosmia, rhinorrhoea, vomiting and diarrhea, while
10 to 30% of infected persons remain asymptomatic (Marian 2021).
Antibody production has been documented in patients with acute infection
within 21 days post infection onset, whereas persons with mild symptoms
have low or undetectable levels of antibodies (Long, Liu et al. 2020,
Long, Tang et al. 2020). T cell response has been investigated in
COVID-19 patients after stimulation with N derived peptides using
IFNγ-based enzyme-linked immunospots assays (IFNγ ELISPOT assays)
demonstrating circulation of N-specific precursor cells in infected
individuals. In contrast, low proportions of cells recognizing peptides
derived from non-structural proteins (NSPs) were observed in those
persons (Le Bert, Tan et al. 2020). Recently, preferential T helper cell
type 1 (Th1) responses to S protein have been detected in patients with
acute respiratory distress syndrome at early stages of the disease which
increase over the time (Weiskopf, Schmitz et al. 2020).
The aim of this study was to evaluate the long-term humoral and cellular
immune response to SARS-CoV-2-S-protein comparing individuals
PCR-positive or –negative for SARS-CoV-2 from the first pandemic wave
with Wuhan type SARS-CoV-2 in spring 2020 6 to 9 months after infection.
This study identifies a set of persons diagnosed with positive
SARS-CoV-2 PCR that did not develop positive serological or cellular
immune responses to SARS-CoV-2 and underlines the importance to appeal
to all reconvalescent individuals to get COVID-19 vaccination.