The development of serum proteins and humoral immunity in opossum "embryos".

The development of serum proteins, immunoglobulins and the immune response was studied in opossum embryos'. Serum proteins gradually increased from birth to 80 days of age when adult values were obtained. γM immunoglobulins were found at all stages of development but γG immunoglobulins were less regularly present. Those embryos' which were 5 days or older at the time of immunization had an immune response to bacteriophage f2 and embryos' 15 days or older responded to a hapten determinant, DNP. γM antibodies were most prominent but γG antibodies could also be detected in the immune response of opossum embryos'.