The first reason is the accumulation of lipids in non-fat tissues, including the thymus and bone marrow. Violation of the architecture of immune tissue negatively affects its functions, causing premature aging.
Secondly, the level of LDL* increases, which in turn affects the activity of leukocytes. And a low level of HDL** in the blood plasma leads to the accumulation of excess cholesterol and increased proliferation of bone marrow cells.
*Low density lipoproteins
**High Density Lipoproteins
Thirdly, obesity causes metabolic syndrome, which results in insulin resistance. Insulin has been shown to play a critical role in regulating immune cells by fine-tuning metabolic programming.
Fourthly, obesity contributes to the disruption of the formation of post-vaccination immunity and its rapid weakening. A large Scottish study of 3.6 million people found that 76% of vaccine recipients with a BMI > 40 kg/m2 were more likely to be hospitalized or die from COVID-19.
Fifth, obesity increases the secretion of cytokines and chemokines (markers of inflammation), increasing the number of macrophages in adipose tissue. Local and systemic inflammation increases in the body, which has been proven by many studies using the IN VIVO method.
Source: Ginzburg A. S. Paradoxes of the immune response in obesity (in Russian)