Influence of size and gene dosage on the survival of skin allografts on rats rendered tolerant at birth.

Abstract

In most studies on the phenomenon of immunological tolerance as it applies to the cellular antigens responsible for transplantation immunity, neonatal mice or rats are inoculated with suspensions of living, allogeneic cells and, when immunologically mature, challenged with skin allografts of the same genetic origin as the putative tolerance-conferring stimulus. If such grafts are accepted permanently, the animals are judged to be highly or completely tolerant, whereas if the grafts outlive those on untreated recipients but are eventually rejected, the hosts are considered partially or incompletely tolerant. Although there is evidence that exposure to the test graft may sometimes augment the degree of unresponsiveness induced at birth (1), it has generally been assumed that such grafts are indicators of, rather than contributors to, the immunological states of their hosts. We here provide evidence that this assumption is incorrect. Our results indicate that the attributes of the test grafts that putatively tolerant rats are challenged with influence their immune response. Our findings also indicate that the survivals of these grafts are determined by the same factors that operate when only weak histoincompatibilities prevail. Materials and Methods Rats. Major histocompatibility complex (MHC)-incompatible BN/Ss (BN; RTI") andLewis/Ss (Lew; RT11) rats, as well as their F1 hybrids (Lew/BN), were used. The median survival time (MST) of BN (or Lew/BN) skin on adult Lew hosts is ~ 10 d (1).Because there was no difference in the ability of bone marrow cells from reciprocally produced F1 hybrids to induce tolerance of skin, or of skin from these hybrids to survive on tolerant hosts, the results using them have been pooled. There also was no evidence of a sex difference in tolerance susceptibility. Hence, the results with males and females have likewise been pooled.Tolerance Induction. Tolerance was induced by inoculating rats <20 h old intravenously with suspensions of bone marrow cells prepared from adult F1 hybrid animals according to procedures described elsewhere (2).Skin Grafting. Animals were grafted when 2 mo old. Grafting entailed the transfer of fullthickness ventral-trunk skin. The preparation of the grafts, as well as the operative technique, have been described elsewhere (3). First grafts were always transplanted to the right thorax, and second grafts to the left. When animals were grafted simultaneously with two grafts of

Major histocompatibility complex (MHC) restriction of foreign transplantation antigens in rats rendered tolerant at birth.

“…Surely, if only MHC restriction were involved in determining the fate of third party grafts on tolerant animals, one would not have expected two of eight Lewis rats rendered tolerant at birth with (Lewis X DA)F, hybrid BMC (and bearing [Lewis X DA]F, hybrid skin grafts), to have accepted (BN .B4 X Lewis)F, hybrid skin grafts for >50 d. Accordingly, we believe that the heterozygous nature of these third party grafts, along with the amount of tissue transplanted (each recipient received two grafts), somehow induced unresponsiveness to their foreign antigens . This presumption is not without precedence, as it is in complete accord with a previous observation that, despite the fact that on the basis of MHC restriction Lewis rats rendered tolerant with (Lewis X BN)F, hybrid BMC should accept Skn-incompatible BN skin grafts more readily than (Lewis X BN)F, hybrid skin grafts, the opposite is the case, especially if the grafts are large (7) .…”

“…The other group received two (BN.B4 X Lewis)F1 hybrid grafts . It was deemed important to keep graft dosage as constant as possible since it is known that the size of a test graft can influence its survival on a putatively tolerant animal (7). For comparison, (Lewis X DA)F1 hybrids also were challenged with two (BN .B4 X Lewis)F 1 skin grafts .…”

Intrathymic Tolerance Induction: Determination of Tolerance to Class II Major Histocompatibility Complex Antigens in Maturing T Lymphocytes by a Bone Marrow‐Derived Non‐Lymphoid Thymus Cell

“…It seems that differences in the extent of tolerance induction that can be demonstrated in in vitro assays remain undetectable over a broad range in a skin graft rejection assays. Secondly, there is increasing evidence that skin grafts do not provide reliable information about the induction of tolerance to class I antigens, A high variability in graft acceptance has been described, depending on the kind of skin used and the location of the skin implantation [35,36], We feel that an allogeneic CTL assay provides more reliable information.…”

Some Immunological Considerations in Liver Transplantation

“…In our experience, kidney transplant survival exceeds that of heart transplants which, in turn, are favored over skin grafts. Even where skin grafts are concerned, it has been reported that large skin grafts may survive better than do small ones (15); recent experiments by Silvers and colleagues, in which immunological tolerance in rats is reinforced by large skin grafts but not by small ones, may be relevant (16).…”