Immunological protection of the vulnerable marsupial pouch young: two periods of immune transfer during lactation in Trichosurus vulpecula (brushtailpossum)

Marsupial young are born with an underdeveloped immune system and are depen dent upon passively acquired immune protection provided by the mother's mil k. Colostrum and milk samples were collected from the brushtail possum thro ughout lactation and the concentration of secretory IgA (sIgA), IgG and tra nsferrin was determined by Western blotting. Two periods of immune transfer were identified. The first, a colostral phase, occurs immediately after bi rth and involves sIgA, IgG and transferrin. During the early lactation stag e, pouch young receive milk of a unique composition as they undergo develop mental changes in the pouch that occur in utero for eutherian mammals. At t he end of this external gestation, the composition of the milk changes (swi tch phase) to resemble that of eutherian mammals in the late lactation phas e. The second transfer of immunity consists of IgG and transferrin, and occ urs during the switch phase prior to maturation of the immune response. (C) 2000 Elsevier Science Ltd. All rights reserved.