EFFECTS OF ADA INHIBITION ON T CELL DEVELOPMENT IN VITRO.: 8

Abstract

The effects of an induced ADA deficient state on thymocyte development in vitro has been studied in fetal thymus organ culture. Culturing day 16 fetal thymus for 5 days results in the development of normal cortical and medullary thymocyte populations. Thymuses were explanted at various stages of fetal life, day 16 (thymocytes are all large, immature subcapsular cortical thymocytes), day 18 (cortical thymocytes predominate - medullary thymocytes undetectable), and day 20 (both cortical and medullary thymocytes detectable in normal proportions), and incubated at the lowest concentration of inhibitor (both EHNA and DCF were run in separate studies) that produced >90% enzyme inhibition plus varying concentrations of AdR. Control cultures contained AdR or medium only. The results are summarized as follows:a) Day 16 cultures - little increase in cell number and no evidence of cortical or medullary thymocyte development.b) Day 18 cultures - a decrease in cell number and no medullary thymocyte development.c) Day 20 cultures - a decrease in cell number in the cortical thymocyte population with medullary thymocytes unaffected.The day 16 and 18 thymocytes that were incubated in an ADA deficient state had the characteristics of subcapsular thymocytes: they were Thyl+, TdT+ and RT-1+ (histocompatibility antigen). Thus, an induced ADA deficient state prevented the differentiation of subcapsular thymocytes into "mature" cortical and medullary thymocytes.(Supported by NIH grants HD-17061 and HD-00554)