3.1 Cytokine storm in COVID-19
In response to massive amounts of released cytokines, a form of
inflammatory reaction would be triggered, namely cytokine storm
syndrome, that is characterized by higher IL-6 levels. This is obviously
detected in seriously ill COVID-19 patients and may further weaken their
immune response (Dal Moro and Livi, 2020).
Because of the positive correlation between high IL-6 level and COVID-19
severity, IL-6 is specifically suggested to be the master marker used
for monitoring disease progression (Liu et al., 2020b). There a growing
evidence that IL-6 can play a crucial part in the
uncontrolled intestinal inflammatory process, proving its role in the
pathogenesis of COVID-19-asociated diarrhea. However, another causing
factor may be attributed to the direct viral invasion of gut epithelial
cells via ACE-2 (Mudter and Neurath, 2007).
As previously reported, IL-6 could prohibit the olfactory signal
pathway; proposing that anosmia detected in COVID-19 patients may be due
to IL-6-mediated inflammation of the nasal mucosa (Henkin et al., 2013;
Luërs et al., 2020). Besides, other additional elements supporting that
SARS-CoV-2 may have a neuro-invasive propensity to invade the central
olfactory pathway causing an olfactory dysfunction (Marinosci et al.,
2020). Jointly, IL-6 was also found to be extremely involved
in promoting the ocular inflammation; matching with conjunctivitis that
is recently reported to be linked with COVID-19 infection (Ghasemi,
2018).