| Summary: | The influence of the host environment on the differentiation of stem cells was investigated by using irradiation and allophenic chimeras generated with responder and nonresponder mouse strains. By using three different antigens, the synthetic polypeptide (T,G)-A--L and the hormone insulin of beef or pork origin, and a variety of irradiation chimeras P(NR)→F 1(R x NR), P 1(R) + P 2(NR)→F 1(R x NR), or F 1(R x NR)→P 1(NR), it was found that stem cells of nonresponder genotype differentiated into T cells that were of responder phenotype, judged by their capacity to give responses in the presence of macrophage-presenting cells of responder genotype. It was noteworthy, however, that stem cells of nonresponder genotype did not differentiate into responder antigen-presenting cells in a responder environment in an irradiated chimera. The conclusion that T cells of nonresponder genotype differentiate into phenotype responders was confirmed in allophenic chimeras, using insulins as antigens. With insulin by virtue of the species variants the specificity of the response is known, with C57BL T cells recognizing the A chain, whereas BALB/c cells recognize the B chain. Maturation in a chimeric environment was found to alter the recognition capacity of the T cell pool, as judged by the ability of C57BL cells from the allophenic (C57BL ⇆ BALB/c) to recognize B chains also. However, the specificity of functional presentation by macrophages does not change. the implications of these observations for mechanisms of Ir gene action are discussed.
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