FETAL RESPONSE TO ANTIGENIC STIMULUS

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Abstract
Fetal lambs were injected in utero at different stages of gestation and with a variety of antigens. The fetal lamb is able to form large amounts of specific antibody as early as the 70th day of the 150 day gestation period. Among the several antigens employed, the earliest and strongest response was to bacteriophage eX. Slightly less effective was horse ferritin, while ovalbumin proved to be a weaker antigen late in gestation, and non-antigenic before about 120 days. Diphtheria toxoid, Salmonella typhosa, and BCG were ineffective as antigens throughout fetal life. Thus, the timing of immunogenesis appears not to be a unique event, but differs with different antigens. The earliest anti-phage antibody formed in the fetus is a 19S macro-globulin. Only in older fetuses with more prolonged stimuli were appreciable amounts of 7S y-globulin formed.