The origin of immunoglobulins in opossum “embryos”☆

Abstract The appearance of immunoglobulins was studied in newborn and known aged pouch young opossums. Newborn serum collected from the neonate prior to the animals attachment to the teat, was studied for the first time. This newborn serum displayed a total lack of immunoglobulins. However, immunoglobulins were found present 12 hr after attachment and results indicated that the opossum embryos receive immunoglobulins through the mother's milk. The initial absence, the first appearance, and the later increase in concentration of these immunoglobulins was studied in a series of developing embryos using blood serum from known-aged neonates. IgG- and IgM-like serum proteins were identified in the adult opossum and a third protein class with IgA-like characteristics was isolated. Both IgG- and IgA-like antibodies were also identified in opossum milk.