Mastitis (inflammation of the mammary gland), as we can see in the name, is an inflammatory reaction of the dairy cow's organism to the presence of microorganisms in the udder. In inflammation, many of the body's own chemicals are released into the tissue as a result of pathogenic microorganisms and other irritants. These increase the permeability of blood vessels, allowing white blood cells to reach the site of inflammation more easily.
White blood cells are motile cells of the immune system that, in addition to producing antibodies, also take up and consume microorganisms and other solid foreign substances in the animal or human body. The process is called phagocytosis (absorption, ingestion) and cells macrophages, microphages, etc. These cells are called somatic = the body's own because they are a normal part of the body. They only accumulate at the site of inflammation, because they fight infection.
A dairy cow with a healthy udder has about 20,000 - 100,000 somatic cells in milk per 1 milliliter (ml). It is a kind of preventive measure of the organism in case the microbes penetrate into the tissue. The immune systems of animals are still on alert, their cells and antibodies (especially IgA classes) are still present on the mucous membranes, for example, to protect these body inputs from infection. It is similar in the internal organs. The task of the immune system is defense, and therefore it acts as a defender.
After the infection penetrates the mammary gland of the dairy cow, based on chemical signals, the white blood cells actively move to the site of inflammation and their number thus increases. And in clinical mastitis, the value of the number of somatic cells can reach up to 10 million in 1 ml of milk or mammary gland secretion.