Abstract
Previous reports (1,2) have shown that cells capable of producing immunoglobulins are present in the liver of the mouse embryo by the fourteenth day of gestation. When transferred to lethally irradiated hosts, these lymphoid precursors, while dependent upon intact thymic function for their ability to produce detectable specific antibody in response to antigenic stimulation were able to synthesize immunoglobulins in the absence of the thymus. These findings suggested that while the thymus may promote the ability of these lymphoid precursors to form specific antibody, immunoglobulin synthesis per se is independent of the thymus. The initial experiments, however, did not rule out the possibility that the transferred cells may in fact have been post-thymic cells with previously determined antigenic commitment. That is, the immunoglobulins produced by these cells could have been antibodies to antigens contacted shortly after transfer. In this report it will be shown that cells which have the potential to produce immunoglobulins in thymectomized irradiated hosts are present in the yolk sac, placenta, and liver of the mouse embryo prior to the appearance of the thymus.
Materials and Methods. Pregnancies were surgically interrupted at various stages of gestation. The embryos and extra-embryonic tissues were dissected free of maternal tissue; they then were washed twice in cold TC 199 (Difco) in an effort to eliminate the possibility of contamination of the extra-embryonic tissues by maternal blood. Identical organs or tissues from a single pregnancy (5-9 embryos) were pooled in cold TC 199 and the cells were gently dissociated by mincing and aspiration through a 20-gauge needle. The age of the gestation was based on the following criteria: 7-8 days, a well developed ectoplacental cone and early membrane formation; 9 days, a well-developed yolk sac, a conspicuous heart, and no liver pigment; 10 days, early pigmentation in the liver; 11-12 days, a well-pigmented liver and the absence of the thymus.
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