Intraembryonic Origin of Lymphoid Stem Cells in the Chicken: Studies with Sex Chromosome and IgG Allotype Markers in Histocompatible Yolk Sac‐Embryo Chimaeras

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Abstract
Two day old chick embryonic bodies were transplanted onto the area vasculosa of age-matched histocompatible blastoderms, resulting in the development of yolk sac-embryo chimeras. Eighteen of these succeeded in hatching and became adults. Differences in sex chromosomes and in Ig[immunoglobulin]G allotype between the embryo and the yolk sac were used to study the contribution of these 2 components to the lymphoid cell development. At 5-7 wk of age the chimeras proved to be completely normal in the IgM and IgG antibody production against human .gamma. globulin and Brucella abortus and in the lymphocyte responses to phytohemagglutinin and concanavalin [Con] A. For the sex chromosome analyses bursa cells and specifically stimulated B [bursa-derived] and T [thymus-derived] lymphocytes were used. The latter was achieved by stimulating thymus, spleen and bone marrow cells in vitro with anti-Ig and Con A. Only 4 of 1498 mitoses analyzed belonged to the sex opposite to that of the bird. Among the chimeras eleven were marked through IgG allotypes. At the age of 3-20 wk all 11 chimeras showed serum IgG of the embryo allotype and none of the yolk sac type. Based on the use of 2 different markers, lymphoid stem cells in the chicken are apparently originally derived from an intraembryonic source and not from the yolk sac.