A close interaction between the virus SARS-CoV-2 and the
immune system of an individual results in a diverse clinical
manifestation of the COVID-19 disease. While adaptive immune
responses are essential for SARS-CoV-2 virus clearance, the
innate immune cells, such as macrophages, may contribute, in
some cases, to the disease progression. Macrophages have
shown a significant production of IL-6, suggesting they may
contribute to the excessive inflammation in COVID-19 disease.
Macrophage Activation Syndrome may further explain the high
serum levels of CRP, which are normally lacking in viral
infections. In adaptive immune responses, it has been revealed
that cytotoxic CD8+ T cells exhibit functional exhaustion patterns,
such as the expression of NKG2A, PD-1, and TIM-3. Since SARSCoV-2 restrains antigen presentation by downregulating
MHC class I and II molecules and, therefore, inhibits the T cellmediated immune responses, humoral immune responses also
play a substantial role. Specific IgA response appears to be
stronger and more persistent than the IgM response. Moreover,
IgM and IgG antibodies show similar dynamics in COVID-19
disease.