A review of complementary mechanisms which protect the developing marsupial pouch young

Marsupials are born without a functioning adaptive immune system, into a non-sterile environment where they continue to develop. This review examines the extent of exposure of pouch young to microorganisms and describes the protective mechanisms that are complementary to adaptive immunity in the developing young. Complementary protective mechanisms include the role of the innate immune system and maternal protection strategies, such as immune compounds in milk, prenatal transfer of immunoglobulins, antimicrobial compounds secreted in the pouch, and chemical or mechanical cleaning of the pouch and pouch young.

► Marsupials are unable to mount an adaptive immune response at birth. ► Instead, maternal mechanisms and innate immunity protect the developing marsupial. ► Milk contains immunoglobulins, lysozyme, transferrin and immune cells. ► The pouch contains β-lactoglobulin, α-lactalbumin, hornerin and dermcidin. ► Innate immunity involves cathelicidins, which kill a broad range of bacteria.