. 2021 May 5;30:09636897211010632. doi: 10.1177/09636897211010632

Table 2.

Representative Adaptive Immune Cell Subset Changes and Cytokine Secretions in SARS-CoV-2 Infection.

Immune Cell Subset	Changes in Frequency		Changes in Phenotype	Reference
CD4⁺/CD8⁺ T Cell Ratio	Increased ratio indicates poor efficacy after treatment			^20,21,126
CD8⁺ T Cell	Mild	Decreased total number in the peripheral blood. Increased CD8⁺ T cells infiltrate the lungs with clonal expansion. In mild cases, multi-cytokine production of CD8⁺ T cells is higher compared to CD4⁺ T cells	Upon SARS-CoV-2 infection, the circulating peripheral CD8⁺ T cells are activated and produce granzyme B and perforin. In convalescent patients, CD8⁺ T cells recognize the viral spike protein, M protein, and least eight SARS-CoV-2 ORFs	^{8,21,61,68,88,102,127–134}
CD8⁺ T Cell	Severe	Further decreased total number	Circulating peripheral CD8⁺ T cells are activated and produce high amounts of granzyme B and perforin, yet may exhibit increased expression of exhaustion markers, including PD-1, Tim-3, and NKG2A	^{20,21,61,127–129}
CD4⁺ T Cell	Mild	Decreased total number. Decreased T_reg, memory, and effector memory cells SARS-CoV-2 infection can prime CD4⁺ T lymphocytes to differentiate into Th17 and T_FH.	Decreased conventional Th1 and IFNγ secretion Increased pathogenic Th1 cells, which can secrete IL-6 and GM-CSF to induce CD14⁺ CD16⁺ monocyte activation Decreased CD4⁺ naïve, CD4⁺ memory, and effector memory subsets Increased CD4⁺ effector-GNLY subsets	^{21,56,102,122,124,129–131,135–141}
	Severe	Decreased in the most severe cases and increased percentage of over-activated with reduced IFNγ production Increased percentage in the naive subset but decreased in the memory and effector memory subsets. Numbers increase with recovery	Increased CD4⁺ naïve subsets Decreased CD4⁺ memory, and effector memory subsets CD4⁺ T lymphocytes differentiate into pathogenic Th1 cells. Increased CD4⁺ effector-GNLY subsets	^{20,72,124,128,135,142}
Others T cell	Decreased numbers of total circulating γδT cells but increased frequency of CD4⁺ γδT cells			^143–145
B cell	Mild	The humoral response is less affected by the virus. Most convalescent COVID-19 individuals have neutralizing antibodies B cells in geminal center are largely absent during the acute phase	Within 1 week of illness onset, antibodies are detectable in approximately 40% of patients. Fifteen days after infection, the detectable antibody count rapidly increases to 100%, followed by IgM (94.3%) and IgG (79.8%) Specific antibodies against the RBD of the spike protein, SARS-CoV-2 NP, and the main protease Increased active state but decreased memory B cell subsets	^{20,72,124,127,131,135,146–155}
B cell	Severe	Proportion of B cells is significantly higher than in moderate cases		^{20,72,124,127,131,135,146–155}