Relationship between nasal viral load and SARS-CoV-2 antibody
levels
SARS-CoV-2 viral load was measured in nasal wash collected at the first
visit. SARS-CoV-2 was detected in about 48% (25/52) of anosmic and 45%
(24/53) of normosmic patients. Among SARS-CoV-2 positive patients, viral
load was not significantly different in anosmic and normosmic patients
(data not shown). Anosmic patients tended to have higher levels of
SARS-CoV-2 specific nasal and serum IgG and this difference reached
significance for RBD IgG in nasal wash (Figure 2a) . No
significant difference was observed for nasal or serum IgA. These
results contrast with our previous report indicating that patients with
prolonged anosmia had lower levels of nasal, but not serum IgG, 2 months
after onset of symptoms7. This difference suggests
that anosmia is associated with dynamic changes in antibody levels that
may be related to the changes in SARS-CoV-2 antigen
load16. The association with serum and nasal IgG, and
not IgA, levels suggests that antigen challenge occurs at the systemic
level. To further explore the relationship between viral replication and
antibody levels, nasal SARS-CoV-2 PCR-positive and negative patients
were compared. Among anosmic patients, SARS-CoV-2 PCR-positive patients
had lower levels of nasal and serum IgG as compared to SARS-CoV-2
PCR-negative patients (Figure 2b) . A similar trend was observed
for nasal IgA levels. In serum, SARS-CoV-2 negative patients had higher
levels of SARS-CoV-2 specific IgA, contrasting with IgG levels. Similar
opposite trends for serum IgG and IgA levels have been observed in
previous studies of COVID-19 convalescent patients, although the
mechanism involved has not been determined17.
Among SARS-CoV-2 PCR-positive patients, a negative correlation was
observed between SARS-CoV-2 viral load and nasal and serum IgG and IgA(Figure 2c) . Together these data suggest that, among patients
with more severe OD, SARS-CoV-2 replication in the nasal cavity may be
controlled by the presence of high levels of IgG and IgA. The most
significant negative correlations were observed with antibodies to RBD
and S1 subunit, suggesting that neutralizing antibodies may play an
important role (Figure 2c) . As the relationship between viral
load and levels of antibodies was observed in both nasal wash and in
serum, both mucosal immunity and systemic immunity transferred to the
mucosa may participate in the control of nasal SARS-CoV-2
replication18. Surprisingly, no significant
association between nasal SARS-CoV-2 viral load and antibody levels was
observed in normosmic patients (Figures 2b and 2c) . This
intriguing observation suggests an interaction between more severe OD
and antibody-mediated control of SARS-CoV-2 replication in the nasal
cavity. Such interaction may involve other immune effectors, including
innate immune cells, participating in the anti-viral activity of
antibodies19.