A SECOND STUDY ON THE H-Y TRANSPLANTATION ANTIGEN IN MICE.

Abstract

In mice,H-Y, a histocompatibility locus on theY-chromosome, is responsible for the rejection of male skin isografts by females of many isogenic strains. As a histocompatibility locusH-Yis unique and important experimentally because of its apparent lack of alleles and its absence in females (§1). Using mice of theC57BL/6 strain, where theMSTof male to female grafts is 25 ± 2.5 days, a comparison has been made of the various means by which adult females can be rendered unresponsive of theYantigen (as revealed by inability to reject male skin isografts). The extent to which these various tolerance-inducing procedures result in the establishment of detectable levels of cell chimerism, and the susceptibility of these tolerant states to abrogation by transfer of isologous lymphoid cells have also been investigated. A high proportion of adultC57 females were rendered tolerant of theYantigen following: (a) Intravenous or intraperitoneal inoculation of very high dosages (at least 500 million) of isologous male spleen cells. The former route was the more effective, and repeated exposures to the antigenic stimulus were more effective than single ones (§4.1). (b) The receipt of orthotopic skin grafts from infantC57 males (§4.2). (c) Multiparity byC57 males (§4.3). (d) About 3 weeks’ parabiotic union with isologous males, or isologous females which were themselves to lerant of theYfactor as a consequence of neonatal inoculation with isologous or even homologous (Astrain) male cells (§4.4). Parabiosis with females rendered tolerant through multiparity was ineffective. Furthermore, parabiosis of specifically sensitized females with isologous males did not affect their immunological status. Indeed, some of the male partners succumbed to 'parabiosis intoxication'. A sensitive test for chimerism was developed, capable of revealing the presence of as few as 12500Y-antigen-containing cells in a standard test population of 20 million spleen cells (§6.1). On the basis of this test (§6.2), females rendered tolerant by inoculation of isologous male cells at birth, or in adult life, were chimeric as were females neonatally inoculated with (CBA×C57)F1spleen cells. Chimerism was infrequent in females rendered tolerant by neonatal injection of homologous marrow cells. It was consistently demonstrable in females rendered tolerant by parabiosis with isologous males but not in females which had been made tolerant by parabiosis with females rendered unresponsive by neonatal injection with homologous (AU) marrow cells, or in females rendered tolerant by multiparity. These findings indicate that apparently similar states of tolerance of theYfactor can be induced in adult hosts by two widely disparate antigen dosage ranges (§7.2), achieved by different regimens of administration or exposure. The lower effective dosage ranges do not result in the establishment of detectable levels of cell chimerism. Attempts to induce tolerance of theYantigen by means of single or multiple, spaced intravenous or intraperitoneal injections of very low dosages (ranging from 7 × 103to 2 × 106) of isologous male splenic cells were only marginally successful (§4.5). The results of studies on the abolition of tolerance of theYfactor by transfer of isologous lymphoid cells from specifically sensitized females (§5; §7.5) indicated that a necessary condition for abrogation of tolerance was a demonstrable level of chimerism. Putatively non-chimeric or very low level chimeric tolerant females were unaffected by the intraperitoneal transfer of even three donor equivalents of immune cells. However, such animals could easily be made susceptible to adoptive immunization either by giving them a second isograft of male skin, or by increasing the number ofY-antigen-containing cells in their bodies by injecting them with 20 to 30 million isologous male spleen cells, at about the time of transfer of immune lymphoid cells. These findings suggest that when lymphoid cells are transferred from a sensitized to a tolerant, or probably even to a normal host, further antigenic stimulation is necessary to make them immunologically effective (§7.5). Possibly the transferred cell population does not include enough ‘ready-made’ cells of the type that can immediately circulate in the blood stream and infiltrate and mount an effective immunologic attack upon a well established ‘target’ graft. The phenomenon of ‘split-tolerance’ is discussed in relation to some new observations bearing upon it (§7.4), which suggest that the phenomenon may apply to homologous as well as toF1hybrid cellular inocula.