Multiple immune function impairments in diabetic patients and their effects on COVID-19

Table 1 Impaired immunity against coronavirus disease 2019 in patients with diabetes

Type of immune response	Immune cell type	Immune cell abnormalities that cause COVID-19 exacerbation in diabetes
Innate immunity	Dendritic cells	(1) Hyperglycemia promotes DC maturation and apoptosis[15-17]; (2) Reduction in quantity[17]; and (3) Abnormal function: IFN-α[18]
	Macrophages	(1) Macrophages accumulate in the lungs[26,29]; (2) Increased numbers of M1-type macrophages[29]; and (3) Macrophages may promote inflammatory storms and DIC of COVID-19[30]
	Neutrophils	(1) Neutrophils are more prone to NETosis in diabetes[34]; and (2) Diabetes may increase ACE2 expression, which mediates enhanced neutrophil infiltration[36,37]
	NK cells	NK cell levels increase but activity decreases and function abnormally in diabetes[41,42]
	NKT cells	NKT cells were inversely associated with diabetes progression or COVID-19 severity[46]
Adaptive immunity	B cells	Changes in the number, phenotype, and function of B cells in diabetic patients may exacerbate the abnormal response to COVID-19[51]
	T cell	The higher correlation between CD4 T cells and antibodies targeting the S1 domain of the spike protein leads to the worsening of COVID-19 in diabetes[53]

COVID-19: Coronavirus disease 2019; IFN-α: Interferon-alpha; ACE2: Angiotensin converting enzyme 2.