It is known that the introduction in a normal subject of cells or tissues from an animal of another species or even a transplant from the same species will induce the appearance of defense processes. These differ with the degree of heterogeneity of the transplant. Experimentally, we can vary this degree of heterogeneity of transplanted cells and study the different responses in the frame of the normal and abnormal defense mechanism.

For the highly heterogeneous transplant, such as cells or tissue of a strange species, a primary response occurs, with liberation of hydrolytic enzymes and lipids. If sufficiendy strong, this response will destroy and eliminate the transplant. If the transplant is moderately heterogeneous, such as one from an individual of the same species, the primary reaction is milder so that the transplanted tissue survives this attack. It will, however, be killed and rejected with the appearance of the second defense stage, i.e., that of the allergic reaction. The damage to the transplant can be attributed to the antiheterogeneous reaction, which this time appears to be directed toward the product resulting from the bond between the transplant and tissue allergic antibodies.

For a still less heterogeneous transplant, such as one from young animals of the same species, the two defense responses are mild. However, the transplant is often destroyed through a later intervention of immune antibodies. This is seen to occur after some months for organs or for cell transplants such as bone marrow cells for the treatment of severe radiation damage. In these cases, the defense mechanism which intervenes months after grafting can be correlated to the immune stage. An autograft, which is a perfectly homologous transplant, usually will survive. The fate of a transplant thus appears to be determined by its heterogeneity. This heterogeneity, however, does not result only from the differences which exist between donor and receiver. Even an autotransplant can be heterogenized by surgical manipulation, heat or other treatment, or by changing its organizational relationship to other entities, to such a degree as to be destroyed by an immune, allergic or even a primary defense response.

The heterogeneity of the transplant—intrinsic or induced by the application of external agents—represents only one factor which determines the nature of the defense processes. Another factor corresponds to the changes in the antigen or constituents induced by the intervention of primary, allergic or even protective immunological reactions. The study of the defense reaction against the organism's own tissues or cells heterogenized by previous immunological responses is of special interest, in view of the role of such heterogenized entities in a more complex defense mechanism. The organism often heterogenizes its own entities through the agents used in the defense against foreign entities. Primary, allergic and even immune reactions induce various degrees of heterogenization of the organism's own constituents at various levels of the organization.

Through the intervention of hydrolytic enzymes, lipids, allergic antibodies or even neutralizing antibodies, different changes in an organism's own entities can be induced. From these, the heterogenization of body entities by lipids was studied in particular. The heterogeneous effect of lipoacids could be shown in many experiments, as in the following: Suspensions of cells of different organs of guinea pigs, in a concentration of 1 gram of cells to 10 cc.of saline, were prepared. At the same time lipoacid suspensions in saline were obtained starting from 2% solutions of different lipoacids in alcohol. Four weekly administrations to guinea pigs of the separate cell suspensions or of the lipoacid suspensions were not followed in most of the animals by any serious manifestations. A heterogenization of the cells was obtained through the action of the lipoacid suspension upon the cells. While one single injection of the so treated cells showed no noxious manifestations, consecutive injections at weekly intervals were seen to induce, in less than a month, important changes generally concerning the respective organs from which the cells derived.

The lipoacid cell complex acts as an antigen, with the type of cell determining the organ where the abnormal changes will occur, and the lipid determining the character of the occurring reaction. Depending upon the lipoacid, the effect will vary from minimal tissular lesions all the way to massive degenerative changes leading to death.

The degree of heterogeneity of the lipoacid appears to be one factor which determines the stage of defense induced. Oleic and linoleic acids, and the lipoacids from human placenta, cow liver or total body of guinea pigs had a slighter effect in inducing organ lesions than the lipoacids obtained from Bixa orellana and especially from the tubercle bacilli which led to serious damage in the respective organs. Tuberculin acting upon the cells had the same effect as lipids obtained from tubercle bacilli.

Through variations in the nature of the autogenous factors—hydrolytic enzymes, lipids, allergic antibodies or even immune antibodies—a graduated series of changes in an organism's own entities can be induced. Of the factors which intervene in the heterogenization of such entities, we have studied the lipids in particular. An antigenic role for lipoacids could be shown in many experiments. For example, suspensions of red cells or cells of different tissues of guinea pigs in a concentration of 1 gram of cells to 10 cc. of saline were prepared. At the same time lipoacid preparations were obtained in the following manner. 5 cc. of a 2% solution in alcohol of different lipoacids or mixtures of lipoacids were added to 110 cc. of water and the preparation boiled under low pressure until reduced to 100 cc.

The cell suspensions were administered to guinea pigs in four injections at weekly intervals with no serious manifestations. The same was done for the lipoacids above. A preparation was obtained through the action of the lipoacids upon the cell suspension in the following manner. 5 cc. of the colloidal lipoacid aqueous suspension were added to 5 cc. of the suspension of cells of different tissues. To 5 cc. of red cells, only 1 cc. of the lipidic suspension was added. The mixture in each case was incubated for two hours at 37°C and centrifuged. The cellular residues, separated from the supernatant fluid, were resuspended in saline and kept frozen. While one injection of the so treated cells showed no noxious manifestations, consecutive injections at weekly intervals were seen to induce, in less than a month, manifest changes in the respective organs. With the red cells, a marked anemia was induced. Oleic and linoleic acids, and the lipoacids from human placenta, cow liver or total body of guinea pigs had only a slight effect in inducing organ lesions. The lipoacids obtained from Bixa orellana and especially from the tubercle bacilli led to serious damage in the respective organs and resulted in death usually in less than 3 weeks. Tuberculin in these cases had the same effect as lipids obtained from tubercle bacilli.

The degree of heterogeneity of the lipoacid appears to be the factor which determines the stage of defense induced. The lipoacid cell complex acts as an antigen, with the type of cell detennining the organ where the abnormal changes occurs, and the lipid determining the character of the occurring reaction. Depending upon the lipoacid, the effect will vary from minimal tissular lesions all the way to massive degenerative changes leading to death.

The intervention of a bond between cells and lipids appears evident when acid lipid preparations are injected repeatedly at weekly intervals in the same organ. Lesions are obtained which are similar to but less intensive than those produced by the cell lipoacid complexes.

It was highly interesting to note the differences in lesions depending on the origin of the cells injected. Zones of necrosis, often with subacute cellular degeneration and even with inflammatory processes, were induced by not too heterogeneous fatty acids. Acute glomerulonephritis, liver degeneration, pneumonia, enteritis or encephalitis resulted from repeated injections of cells from kidney, liver, lungs, intestines and brain treated in vitro with bixin, lipoacids of tubercle bacilli, lipoacids of fish or even fatty acid mixtures of cod liver oil.

Against tissue transplants, injections of the host with lipoids with negative character—such as fatty acids, mixture of lipoacids of different origins, and lipids with SH or SeH as polar groups—have exaggerated all phases of defense processes. Skin transplants between siblings, which usually give a high percentage of accepted grafts, were rejected completely after treatment with some of these agents. The degree of heterogeneity of the agents appeared particularly interesting. With lipoacids of the same species, very high doses were required to induce only minimal changes. On the other hand, preparations of lipoacids of fish, mollusk, molds and microbes produced marked effects. Transplants treated with these preparations were rejected or absorbed after eight or more days. Seldom was an immediate rejection seen.

Even more interesting were the results obtained by direct action of the lipids upon transplants, achieving a bond between them. For these experiments, the agents were used in oil solutions as well as in saline suspensions. Transplants were dipped into different preparations. Even autografts if treated with lipoacids of the same species often were rejected. This took place even after more than three weeks. When more heterogeneous lipoacids were used, such as those obtained from other species, autografts were rejected as completely as transplants of the same species, i.e., around the eighth day. This also occurred with relatively heterogeneous agents, such as the lipoids of microbes, especially those of the tubercle bacilli. With still more heterogeneous agents, such as lipoids with SH or SeH polar groups, the treated transplants were rejected through an immediate direct inflammatory reaction.

The influence exerted by injections of the opposite group of lipoids with positive character was in the opposite direction. The percentage of accepted transplants was increased.

By dipping skin transplants of animals of the same species in preparations of the insaponifiable fractions of the species, the percentage of persistent grafts was highly increased. In some experiments all the transplants between siblings were positive. Even between different strains of mice, such positive results were obtained. The treatment of transplants with butanol alone was not effective. Adding butanol to the preparation of insaponifiable fractions, however, enhanced the effect of the latter.

The most interesting results were obtained by cross treatment—in which the transplant was treated with the insaponifiable fraction of the strain of the host and the host with the insaponifiable fraction of the donor. An unusual number of positive grafts were obtained between strains of mice and, in exceptional cases, even between species when a mixture of the two preparations of insaponifiable fractions of the donor and host was used for the treatment of both transplant and host.

Even more interesting results were obtained when, in addition to these treatments of transplant and host, another treatment—that of the "bed" of the transplant—was added. The wound receiving the transplant was soaked with the mixture of insaponifiable fractions. Often after the graft, treatment with the fractions was continued through small injections into the bed of the transplant. Injections into the transplant itself, if possible, increased the number of positive results.

Before pursuing further the study of these interesting problems, an analysis of another aspect of the response to heterogenized material has appeared necessary. It concerns the intervention of different levels of the organization in the defense mechanism. This was seen to vary according to the degree of heterogeneity of the transplant. The defense processes thus can be limited to the heterogenized entity or to entities of the same level, or they can extend far into the hierarchic organization. With a highly heterogenized material, a broad hierarchic reaction occurs with several superior levels intervening. In these cases primary enzymatic or prolonged processes involve the tissular, organic and systemic levels. With less heterogenization, the ensuing primary reaction is not strong enough to destroy and eliminate the heterogenized entities and an allergic reaction takes place. This involves other levels such as tissular and even organic. With still less intensive heterogenization, the defense remains localized at the affected level itself and is weaker. With the defense inefficient in its primary or allergic stages, a protective stage becomes necessary in order to take care of the heterogenized entities.

The analysis of many conditions indicates the importance of the different factors for the development of the clinical manifestations.