Further Studies on Serum Protein Formation by Chimeras ∗ II. Induction of Chimerism with Sublethal X-Irradiation and Heterologous Antiorgan Serum

Abstract

It has been shown that heterologous antiserum against lymphocytes (ALS) or thymocytes (ATS) is a potent immunosuppressive agent and significantly prolongs survival of allografts or xenografts of skin or other organs in animals so treated (1–4). However, its prolonged administration is accompanied by many untoward side effects many of which are incomptaible with host survival (5, 6). On the other hand, although allogeneic or xenogeneic bone marrow transfer protects lethally irradiated mice from radiation death, there is still a very high incidence of fatal secondary disease (7, 8). The present experiments were designed to induce xenogeneic chimerism using a combination of sublethal X-irradiation and the administration of small quantities of ALS or ATS in order to avoid the many systemic complications that may be encountered when either of these procedures is used alone.

The synthesis of donor type serum proteins by tissues in vitro from postirradiation ratinto-mouse chimeras has been demonstrated previously (9, 10) by the incorporation of ¹⁴C-amino acids into serum proteins and subsequent autoradiography of immunoelectrophoretic patterns of concentrated culture fluids obtained from these tissues (11). The same method was applied in the present study to determine whether the combination of low dosage X-irradiation and ALS or ATS would be sufficient to permit the survival of the xenogeneic bone marrow cells in their hosts.

Materials and Methods. Prepartaion of antimouse ALS and antimouse ATS. Lymph nodes from the axillary and cervical regions or thymus glands were obtained from C₅₇B1/6 male mice (Millerton Labs., Millerton, N. Y.), weighing 25–30 g. The cell suspensions were prepared by gently pressing the tissue through a 60-mesh stainless steel wire screen into medium 199 (Microbiological Associates, Bethesda, Md.). These cells were washed twice and resuspended in 0.15 M saline containing 0.1% dextran (Pharmacia, Uppsala, Sweden) and 100 IU of heparin/10⁹ cells. The cell suspensions were adjusted to the desired concentration.