Immunology of the mammary gland

The mammary gland is an organ of specific structure whose elementary task is to supply offspring with nutritive and other biologically active substances during the first weeks, or, depending on the species, the first months of life. This prolongs the period of close contact between the mother and her young, which is necessary for their regular growth. Most mammal offspring are born with physiological agammaglobulinaemia, because of the specific structure of the placenta, so that they receive the first specific protection against pathogenic microorganisms through colostrum. Furthermore, this gland is in direct contact with the outer environment through the secretary ducts, so that there are great possibilities for the occurrence of infections. It is therefore necessary to secure protective mechanisms which would prevent such infections. It is clear that there is a distinct connection between the immunological system and the mammary gland, and that link is the central topic of this paper. It presents the basic mechanisms of mammary gland defense which are divided into two categories: nonspecific (innate) and specific immune response. The mammary gland secretion contains several types of leukocytes, such as lymphocytes, macrophages, and neutrophiles, as well as 2% epithelial cells. On the average, there are 0.2 x 106 somatic cells in one mililiter of milk. Macrophages account for most of these (58%), as well as lymphocytes (28%), while a smaller number of somatic cells (12%) are polymorphonuclears (PMN). The paper considers the characteristics and main functions of these cell types.