Influence of Lymphopoiesis Control Mechanisms on the Recovery of Immune Capacities in Isogenic Radiation Chimeras

The capacities of cells belonging either to foetal liver or to adult bone marrow or spleen are extremely different as far as the production of immunologically competent cells (ICC) by isogenic chimeras is concerned. The study of thymectomized radiation chimeras by the Simonsen test and the Jern technique shows that it is only the spleen or the lymph nodes which are able to bring ICC to a thymectomized animal; the bone marrow and the foetal liver carry only precursor cells which cannot be transformed into ICC when the recipient lacks its thymus. Furthermore, the functional ICC brought to these animals by the spleen cell suspensions have limited life span, not exceeding 300- 400 days. It must also be stressed that the thymectomized isogenic chimeras treated by bone marrow or foetal liver, although they display no immune reactivity, have an increased production of immunoglobulins. Therefore it seems that in this case there is no regulation of the production, differentiation and maturation of ICC. However, a control of the production and/or reactivity of ICC does exist in non-thymectomized radiation chimeras. This can be shown by the Simonsen test and the Jern technique for the primary reactions and by the study of homologous tumour graft rejection for the second-set reaction. This regulatory activity could be mediated either through a feed-back mechanism acting on ICC production or through a more complex process involving an interaction between antigens and cells. (author)