Cytokine storm:
It is well observed clinically that one of the main causes of
deterioration of patients’ clinical conditions is the significant
increase of proinflammatory cytokines levels in their sera suggesting
the importance of this immune defense mechanism in the pathological
processes of this disease(27). This huge increase in cytokines levels or
what is known clinically with cytokine storm, could lead to serious
pathologic findings including increased vascular permeability, increased
blood viscosity, deteriorated pulmonary functions which could be
associated with multiple organ failure and death(63).
A study which compared COVID-19 patients who were admitted to ICU units
with clinically stable patients and normal controls found that there was
noticeable increase in serum levels of certain cytokines including
IL-1β, IL-1ra, IL-7, IL-8, IL-9, IL-10, basic FGF, G-CSF, GM-CSF, IFN-γ,
IP-10, MCP-1, MIP-1α, MIP-1β, PDGF, TNFα, and VEGF in ICU and stable
patients in relation to the third group. In specific, IL-2, IL-7, IL-10,
G-CSF, IP-10, MCP-1, MIP-1α, and TNFα were even higher in those admitted
to ICU compared with the clinically stable patients highlighting the
role of the cytokine storm in worsening the patients’ clinical
conditions(64). Another study showed similar findings suggesting the
relation between the increase in proinflammatory cytokines levels and
the occurrence of serious lung pathology (65).
The cytokine storm has been proposed to be in part due to abnormal GIT
microbiota features which have normally important role in maintaining a
balanced host immune response. In a study which involved 366 study
subjects, it was found a significant correlation between microbiota
disturbance and uncontrolled production of inflammatory cytokines
suggesting a relation between COVID-19 cytokine storm and microbiota
patterns. Examples of these microbiota are
Bacteroides genus, Streptococcus genus and Clostridiales which had
negative correlation with the measured proinflammatory cytokines while
Ruminococcus genus, Blautia genus and Lactobacillus genus had positive
correlation (66).