Reversal of Wasting Syndrome in Thymectomized Mice by Multiple Syngeneic or Allogeneic Thymus Grafts2

Abstract

Restoration of normal immunologic development with reversal of wasting syndrome is described in wasted thymectomized mice receiving multiple grafts of newborn syngeneic or allogeneic thymus. Recovered mice showed normal development of lymphoid tissues and immunologic capacity as measured by homograft rejection and graft-versus-host reactivity of spleen cells. Twenty-three of thirty-five wasted mice receiving five syngeneic thymus grafts recovered. In contrast, only 2 of 15 given single syngeneic thymus grafts recovered, whereas 9 of 15 survived with persistent wasting, lymphoid hypoplasia, and immune deficiency. Sixteen of thirty wasted mice receiving multiple allogeneic thymus grafts recovered. When host and donor shared the same H-2 locus, 12 of 14 recovered; 9 of these 12 became cellular chimeras with the thymus donor strain. When host and donor differed at the H-2 locus, only 4 of 16 mice recovered and only host-type immunocompetent cells were demonstrable. These experiments indicated that thymus grafts restored immune capacity and permitted reversal of wasting by 1) stimulating development of the host's lymphoid system (humoral), 2) donating lymphoid cells to the host (cellular), or 3) a combination of both mechanisms. With allogeneic thymus grafts, both humoral and cellular mechanisms seemed to contribute if host and donor shared the H-2 locus, whereas humoral mechanisms alone may have been operative in mice grafted with thymus across the H-2 barrier. Multiple thymus grafts were more effective in reversing wasting syndrome than were single thymus grafts, probably because they presented greater humoral stimulation and more lymphoid cells to the host's lymphoid system.