The pathogenesis of the graft-versus-host reaction in chicken embryos. Pathological changes in the yolk sac, thymus, bone marrow and bursa of Fabricius

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Immune reconstitution in the immunodeficient chicken by transfer of embryonic lymphoid cells

Embryonic chickens were rendered immunodeficient by in ovo injection of homologous IgM on the 10th embryonic day. The immunodeficient embryos were intravenously given lymphoid cells taken from normal embryonic bursa, spleen or thymus on the 15th embryonic day. Gain of splenic or bursal weight, natural antibodies to sheep red blood cells (SRBC), frequencies of rosette forming cells (RFC) binding to SRBC or dinitrophenyl-SRBC (DNP-SRBC) and of immunoglobulin bearing cells (IBC) in the bursa and the spleen were investigated to assess the effect of transferred cells during the embryonic stage. Transferred bursal and splenic cells showed an ability to restore the frequency of RFC or IBC in the recipients. However, reversion from the immunodeficient state was not observed in the thymic cell transfer. These findings suggested that the cells derived from embryonic bursa and spleen contained stem cells which developed into RFC and also into precursors of IBC.

A new analysis of allogeneic interactions

Allogeneic reactions have conventionally been considered as typical immune responses by one population of cells to antigens present on the other. This view is inadequate, since it does not explain many features of these reactions, among which are: (1) reactivity is much higher between different strains within a species than between species, in spite of the much greater antigenic disparity in the second case; (2) a very high proportion of cells may respond to allogeneic stimuli; (3) major histocompatibility differences are not essential for vigorous allogeneic reactions; (4) the responding population need not be immunologically competent to respond to antigens of the stimulating population; (5) the stimulating population must be both metabolically active and immunocompetent. We have tried to produce a model of cell interaction which will account for these and other anomalies, which at the same time explaining both normal antigenic stimulation (through cell-cell cooperation) and allogeneic interactions as examples of the same basic mechanisms. The model is based on the Bretscher-Cohn scheme of cell interaction. An allogeneic reaction is seen as having two stages: (1) Cells come together when antibody receptors on cells of one population combine with antigens on cells of the other. To this extent, our model is the same as the conventional one. It need not be the responding population which has the receptors, however. (2) A species-specific proliferation signal passes between the cells. This is the same signal as is involved in normal antibody induction. Even antigen-receptor bonds which are very weak may result in effective stimulation of one or both partners because of enhancing effect of this signal, and because the antigens involved are probably repeated over the cell surface, enabling multipoint binding. This explains the very proportions of cells which proliferate. The exact outcome of any allogeneic interaction will depend on which of the two populations have antibody receptors for antigens on the other, which can produce the proliferative stimulus, and which can respond to either the proliferative signal alone or to this stimulus plus antigen.