Type 2 Diabetes is caused by high blood sugar levels that occur when the pancreas is not able to produce enough insulin. Type 1 Diabetes is caused by high blood sugar levels that occur due to the pancreas not being able to produce ANY insulin.
When blood sugar is high, and the body does not produce enough insulin this can disrupt the body’s immune responses by weakening some of the immune cells that handle the fight against viruses and bacteria (also known as “invaders”).
Think of the immune system as an army made up of many different units that work together to protect the body. There are two main units that provide the first, and second lines of defense against "invaders” like viruses and bacteria that can make us sick. These two “units” are known as the innate and adaptive immune responses, the “fighting power” within each response is done by special cells like neutrophils, macrophages, and T cells. Diabetes causes dysfunction in these cells, and as a result the immune system is weakened (Berbudi et al, 2020).