Common Mucosal Immune System

The human mammary gland is an integral effector component of the common mucosal immune system. However, from physiological and immunological aspects it displays several unique features not shared by other mucosal sites. The development, maturation, and activity of the mammary gland exhibits a strong hormonal dependence. Furthermore, in comparison to the intestinal and respiratory tracts, the mammary gland is not colonized by high numbers of bacteria of enormous diversity and does not contain mucosal inductive sites analogous to the intestinal Peyer’s patches.

Comparative evaluations of various immunization routes effective in the induction of antibodies in human milk are limited. Systemic immunization induces IgG antibodies in plasma but due to the low levels of total IgG in human milk, their protective effect remains unknown. Oral or intranasal immunization or infection induces secretory IgA in milk as demonstrated in several studies.. Because secretory IgA in milk displays protective functions, alternative immunization routes and antigen-delivery systems should be explored.