Immunological mechanisms of increased susceptibility to COVID-19 disease and its severe course in patients with diabetes mellitus type 2 and obesity

In this review, we analyze and summarize literature data and the results of our own research related to the immunity status of patients with type 2 diabetes mellitus (T2D) and those T2D patients who were infected with the SARS-CoV-2 virus. It was shown that in the blood plasma of T2D patients, especially those with ele­vated BMI, the level and ultrastructure of the main cellular components of natural immunity – neutrophils and monocytes – were affected accompanied by high levels of proinflammatory cytokines (IL-1β, IL-6, IL-17 and TNF-α). It was suggested that the increased susceptibility of T2D patients to SARS-CoV-2 infection is primarily­ due to a weakening of the innate immune defense against pathogens, whereas in T2D patients who have COVID-19, adaptive T-cell immunity disorders accompanied by a cytokine storm prevail. It was concluded that hyperinflammation in T2D+COVID19 patients is the result of enhancement of already existing before SARS-CoV-2 infection T2D-caused disorders of innate and adaptive immunity, in the mechanism of which cytokines and chemokines play a significant role. Keywords: COVID-19, cytokines, innate and adaptive­ immunit, neutrophils, T-lymphocytes, type 2 diabetes mellitus