INVASION AND DESTRUCTION OF HOMOLOGOUS KIDNEY BY LOCALLY INOCULATED LYMPHOID CELLS

QUANTITATIVE STUDIES ON THE BEHAVIOR OF SENSITIZED LYMPHOCYTES IN VITRO : I. RELATIONSHIP OF THE DEGREE OF DESTRUCTION OF HOMOLOGOUS TARGET CELLS TO THE NUMBER OF LYMPHOCYTES AND TO THE TIME OF CONTACT IN CULTURE AND CONSIDERATION OF THE EFFECTS OF ISOIMMUNE SERUM

When lymphoid cells, derived from rats immunized with respect to homologous skin, were cultured with target cells originally of donor origin, cytocidal and cytostatic activities of the attacking lymphocytes became evident. By application of a sensitive and reproducible quantitative assay system, various aspects of the mechanism of this destructive interaction between target cells and lymphocytes were examined with the following results. 1. The degree of survival of target cells was inversely related to the number of sensitized lymphocytes. Graphic plots of the data indicated that this relationship was an exponential one similar to "single-hit" inactivation phenomena. One interpretation which could be placed on these results is that a single lymphocyte, if immunologically active, was sufficient to destroy or at least have a detectably adverse effect on one target cell. Furthermore, from such a model it could be computed that, of the lymphocytes derived from an immunized animal, approximately 1 to 2 per cent of the cells were immunologically active; i.e., capable of demonstrable destructive activities against homologous target cells in vitro. 2. Morphological studies on the effect of sensitized lymphoid cells on homologous target cells, aftervarious lengths of time in culture, showed that by 7 hours of incubation, the attacking lymphocytes firmly adhered to the target cells. The cytotoxic effect of these lymphocytes generally occurred after the 20th hour. Quantitative studies supported this conclusion; the latent period, i.e., the time required for detectable degrees of target cell destruction to occur, was approximately 20 hours. 3. A consequence of the incubation of target cells with normal lymphoid cells or even with small numbers of sensitized lymphoid cells was an increase in the rate of division of the target cells. As might be expected, this was reflected in a shorter doubling time of these cells. 4. Extracts prepared from sonically disrupted sensitized lymphocytes proved to be no more deleterious to target cells than similar preparations from normal lymphoid cells. Furthermore, no evidence could be obtained that sensitized lymphoid cells, separated from target cells by a Millipore membrane, were cytocidally effective. These data indicated that if a cell-bound substance is involved in the destruction of homologous cells, either it is not toxic by itself, or it cannot be detached from the sensitized cells. In any case, close apposition of the lymphocytes to the target cells is apparently required for the destruction of the latter in vitro. 5. Serum obtained from immunized animals, if heat-inactivated, did not adversely affect homologous target cells; if employed fresh, slight degrees of toxicity resulted. Specific isoimmune sera did not impart any detectable degrees of immunological reactivity upon otherwise normal lymphoid cells. Immune sera, even in high concentrations, did not augment the effect of sensitized lymphoid cells upon homologous target cells; rather a slight inhibitory effect of these sera was detected. 6. Attempts to detect the presence of complement activity, which might have been provided by the lymphoid cells in culture, were unsuccessful. On the basis of these results, it was suggested that the destruction of homologous target cells by sensitized lymphoid cells occurs as a two step process. First, the attacking lymphocytes attach to their targets via a non-toxic cell-bound substance having an immunologic specificity, and then, destruction of the target cells follows the result of some process dependent on the metabolic activity of the attacking lymphoid cells.

THE ROLE OF LYMPHOCYTES IN THE SENSITIZATION OF RATS TO RENAL HOMOGRAFTS

In order to study the role of blood-borne small lymphocytes in the sensitization of rats to renal homografts 2 techniques for the perfusion of isolated rat kidneys were employed: (a) the in vitro perfusion of kidneys with thoracic duct cells suspended in either an artificial medium or in blood; the perfusates were then injected into rats syngeneic with the lymphocyte donors; (b) the in vivo perfusion of kidneys with blood issuing from the femoral artery and returning to the femoral vein of living rats. The degree of sensitization conferred on the recipients by the perfusates was assessed by applying a skin homograft from the kidney donor and scoring the epithelial necrosis at 6 days. The in vitro experiments indicated that parental strain thoracic duct cells, which had passed through an F₁ hybrid kidney could confer upon a parental rat sensitivity to an F₁ skin graft. Several perfusions with radioactively labelled lymphocytes showed that the injected cells migrated to the lymph nodes and spleen of the recipients Labelled large pyroninophilic cells were occasionally seen in the spleen and lymph nodes of recipients, and it was suggested that these had arisen from the injected cells. Although the in vitro perfusions with blood indicated that renal homografts might sensitize their hosts within 1 hour, the in vivo perfusions suggested that about 5 to 12 hours were required. The more rapid sensitization in vitro was possibly due to the more frequent opportunity for contact between lymphocytes and kidney vascular endothelium which was afforded by the conditions in vitro.

The cellular basis of the local graft-versus-host reaction in rat kidney

Injection of parental strain rat lymphocytes under the kidney capsule of semi-allogeneic F1 recipients causes a local graft-versus-host reaction (GVHR) characterized by a heavy mononuclear cell infiltrate and renal tubular destruction. Since the cellular events involved may have relevance to allogeneic tissue damage in GVH disease and allograft rejection, a detailed analysis of the rat renal GVH reaction was performed. A purified CD4+ lymphocyte subpopulation was as effective in mediating a local GVHR as unfractionated parental lymphocytes, but neither naive CD8+ nor specifically sensitized CD8+ lymphocytes produced a detectable renal GVHR. Mononuclear cells harvested from renal GVHR lesions induced by CD4+ lymphocytes were able to lyse natural killer (NK)-sensitive targets when tested in vitro, but showed no allospecific cell-mediated cytotoxicity. Experiments using recombinant PVG rats demonstrated that the ability of the injected cells to cause a GVHR was dependent upon a disparity in MHC class II antigens and that an isolated disparity of MHC class I antigens alone was not a sufficient stimulus to provoke a response. The use of chimaeric rats demonstrated that F1 MHC alloantigens present on kidney parenchyma (but absent on bone marrow-derived cells) were not sufficient to stimulate injected parental lymphocytes, even in the presence of markedly increased amounts of MHC antigens on vascular endothelium and renal tubular cells following in vivo administration of interferon-gamma (IFN-gamma). These results suggest that the renal GVHR in the rat is mediated principally by the interaction of parental CD4+ lymphocytes recognizing and responding to class II F1 alloantigens on bone marrow-derived cells. The resulting tissue damage is most likely a result of a delayed-type hypersensitivity (DTH) phenomenon.

Ontogenic development of contrasuppression

Using a xenogeneic graft-versus-host assay system, we have been able to document the sequential appearance of certain regulatory cells in newborn mice. Before birth, mouse spleen cells exhibit potent suppression that cannot be ameliorated by contrasuppressor cells. On the day of birth, the spleens contain equally potent suppressor cells, but these cells now can be inhibited totally by contrasuppressor cells. Between days 1 and 2 after birth, suppression, as picked up by our system, has disappeared. However, it can be found hiding behind contrasuppressor cells, as elimination of the latter cells with appropriate antisera reveals cells with the same suppressive potency as spleen cells taken 1 or 2 days earlier. Further, if the thymus is removed on the day of birth or 1 day later, the suppressor-obscuring cells do not appear. Thus, there appears to be an inherent ontogenic schedule that the thymus follows, which determines the time when different regulatory cells will emerge from it.

[Immunologic mechanism following liver transplantation. An experimental study in the rat]

To investigate the immunological status of hepatic grafts we transplanted livers from different inbred rats orthotopically on 58 LEW rats; rearterialization of the grafts was achieved with an hepatico aortal segment of the donor. Survival time depended on the donor strain; LBNF1-allografts survived in 67% (n = 12), WiS- in 60% (n = 20) and BUF- in 43% (n = 14) indefinitely. In the DA-to-LEW-combination we found no long-term survivor. Liver perfusates (LP) were prepared from 10 BDE and 10 LEW; after keeping the livers for 6 h at room temperature we perfused via portal vein with 2 ml/g Ringer's solution five times. The treatment of BDE-kidney recipients (LEW) with LP showed prolonged survival; at 5 days application 10.2 +/- 1.3 d (control: 6.5 +/- 0.5 d; P less than 0.001), at 10 days treatment 15.3 +/- 7.3 d. In vitro LP inhibited the PHA-stimulation of LEW lymphoid cells in more than 90% and the ConA-stimulation of LEW spleen cells in more than 95%. In MLC LP showed strong inhibitory effect (inhibition rate greater than 97%) even when different combinations of responding and stimulating cells were used. We assume that an unspecific immunosuppressive hepatic factor is released from ischemic damaged liver grafts which is able to prevent rejection in the induction phase. In WiS-liver recipients surviving for more than 4 months GvHR was tested after splenectomy with spleen cells. All tests showed a grade III reaction. Donor-specific skin grafts which were transplanted on these recipients survived indefinitely while third party skin grafts were regularly rejected (7.6 +/- 0.5 d). We therefore can conclude that the cellular immunosurveillance is intact, but the immunological response against donor-specific antigens is reduced. With transfer of serum from long-term-surviving WiS-liver recipients (greater than 6 months) WiS-kidney grafted LEW were able to survive also prolonged (20.7 +/- 3.4 d, control 6.2 +/- 1.0 d; P less than 0.001). Lymphoid cell transfer (1 X 10(8)) did did not result in significant prolongation of survival time (8.0 +/- 2.0 d). These observations suggest that in the steady phase specific humoral transfer factors are responsible for prolonged survival of hepatic grafts.

Successful cardiac allografts in syngeneic radiation chimeras

Successful cardiac allografts were accomplished across the major histocompatibility complex of rats. LEW and F344 (Ag-B2) rats were lethally irradiated and grafted with WF (Ag-B1) hearts on day 0. Either on day 0 or day 2, the hosts were repopulated with syngeneic hemopoietic cells. The best results were obtained (86%) when a mixture of 3.0 x10(7) non-adherent syngeneic bone marrow and thymus cells were used to repopulate the recipients. In contrast, all of the WF to LEW heart grafts were rejected within 30 days if syngeneic thoracic duct and bone marrow cells were used to repopulate the host. Tolerant rats bearing a functioning WF heart graft were able to mount a normal antibody response to SRBC and a proliferative response to Con A. They accepted a second WF heart or a WF kidney graft but rejected WF skin and bone marrow grafts as well as "third-party" ACl or BN hearts. The lymphocytes of tolerant rats had a reduced response to WF antigens as assayed by local or systemic graft-versus-host reactions in (LEW x WF)F1 recipients. Tolerance to the WF hearts was resistant to a large innoculum of normal spleen and lymph node cells. The unresponsive state could be transferred to unirradiated LEW rats with a mixture of spleen, thymus, lymph node and bone marrow cells.

[Suppression of the cell-mediated immunity in minor histoincompatible rat kidney allograft recipients (author's transl)]

To study the immunological status of recipients of major compatible and minor incompatible kidney allografts, we transplanted FiS and FLF1 kidneys into LEW rats. Most of the FiS kidneys were rejected within 55 days. Of 24 recipients, only 4 survived longer than 4 months. However, two-thirds of the FLF1 recipients survived longer than 4 months. The other third died with 64 days. During the first postoperation week a high level of lymphocytotoxin was detected in the serum of the FiS kidney recipients. Thereafter hardly any alternation of its titer was found, and no variation among the recipients of major histocompatible kidney allografts was shown. The FLF1 kidney recipients showed a low titer of antibody. The hemagglutinin titer showed the same trend as the lymphocytotoxin titer. A blocking serum factor could not be found in the serum of the kidney recipients with the microcytotoxity assay method or with the allorosette-formation inhibition test. Cellular immunity, which was studied with the GvH-reaction and microcytotoxity assay, was detected in the first postoperative week. However, this immunity was gradually supressed, and after 6 weeks was no longer to be found. This immunological status remained unchanged in the indefinitive surviving kidney-recipients in spite of antigen inoculation with two skin allografts of donor origin. This immunological status could be defined as "graft acceptance".

3H-deoxythymidine incorporation in graft-versus-host disease in the Norway rat. II. Autoradiographic studies

A sequential analysis was made of various areas within the lymph nodes and spleen of newborn Brown Norway (BN) rats suffering from graft-versus-host disease (GVHD) subsequent to an allogeneic injection of adult Lewis (L) lymph node cells (experimental). One micron thick autoradiographs were compared between such experimental and control littermates having received the same number of syngeneic adult BN cells. Both experimental and control animals received tritiated deoxythymidine (3HdT) one hour before killing. The autoradiographs revealed a 2.25 and 2.50 times higher thymidine labeling index of lymphocytes in the deep cortex of mesenteric lymph nodes and white pulp of the spleen, respectively, for experimental animals. The experimental effect occurred within one day. The majority of the labeled cells in experimental animals were large lymphoblasts with prominent nucleoli. The labeling index within these areas remained significantly higher than control values until day 8 in the spleen and through day 14 within the lymph nodes. However, differences in labeled cells present in high powered microscopic fields reached a peak on day 3 within compartments in experimental animals but fell significantly below control values by day 9 owing to a pronounced disappearance of both small and large lymphocytes from these areas, and a decreased intensity of individual cell labeling as the reaction progressed. In contradistinction the concentration of labeled cells present in high powered microscopic fields of lymph nodes' medulla became 3.13 times controls by day 4. Most of these labeled cells contained a more basophilic cytoplasm than those found in the deep cortex and some were distinctly plasma cell precursors. In contrast to the deep cortex their concentration remained approximately three times control values until death. The data indicates that the major proliferative events within the spleen and lymph nodes in neonatal rat GVHD are initially restricted to donor cell localization areas of these tissue compartments. Subsequently the GVHD-related events may be attributed to other areas and possibly cell types. Thus any proliferation contributing to splenomegaly in the latter stages of GVHD appears to occur in the red pulp and that contributing to lymph node enlargement a medullary response.

The pathology of renal homograft rejection. A review

Images

[Immune status of indefinitely surviving rat renal allograft recipients after short course of ALS-treatment Detection of a serum blocking factor by allorosette formation inhibition test (author's transl)]

53 LBNF1 kidneys were grafted into L-rats. 24 untreated recipients served as control and survived 16.1 +/- 1.7 days. 14 recipients were treated with 4 ml alloantiserum (ADS) each, and the other 15 animals with 4 ml ALS each. 9 and 10 of these 14 and 15 animals survived for more than 4 months. We performed GvH-reaction with spleen cells of these 19 animals. It showed normal cellular immune response. After splenectomy first donor specific skin was transplanted, 18 days later second skin of same origin (LBNF1) and 18' days after third party skin (LBufF1). The first grafts survived 13.1 +/- 1.9 days in the recipients of ADS treatment and 12.2 +/- 1.2 days in the recipients of ALS. Second skin grafts were rejected delayed in the former recipients as the first grafts, in the later more accelerated than the first grafts. The third grafts survived as the controls. Before and after skin grafting we could not detect lymphocytotoxin and hemagglutinin. The sera of animals with ADS therapy inhibited the spontaneous allorosette formation to 46.0 +/- 4.4% and of ALS therapy 37.7 +/- 9.2%. Our results suggest that after ALS treatment blocking antibodies were produced in the recipients and they cause the enhancement of kidney allograft.

Local renal graft-versus-host reaction: sequential ultrastructural study

A sequential study has been made of the ultrastructure of local renal graft-versus-host reactions produced in cyclophosphamide-pretreated rats by injection of either allogeneic or xenogeneic (mouse) spleen cells beneath the renal capsule. Early in the reaction, immunoblasts were seen between the outer cortical tubules, and there was associated interstitial oedema and tubular degeneration. In places, several small lymphocytes were observed clustered around and in close cytoplasmic contact with individual immunoblasts, perhaps representing interaction between donor and host cells. As the reaction proceeded, the number of lymphoid cells increased by immigration from peritubular vessels. Some tubules were invaded by lymphocytes but this was not closely related to the development of tubular injury. The reaction was maximum at one week and then decreased. Now, there was greater diversity of cells including macrophages, plasma cells and eosinophils, while many lymphoid cells became necrotic. It is concluded that most of the renal parenchymal injury is due to chemical mediators liberated from the infiltrating cells rather than to ischaemia or direct cytoplasmic interaction between leucocytes and tubular epithelium.

Antilymphocyte antibody purified by immunoabsorption and elution

A comparison has been made of several techniques for the preparation from antilymphocyte serum of pure antilymphocyte antibody by absorption on, and elution from mouse thymocytes. The best yield was obtained by a batch method using cells fixed in 0·1% formaldehyde as immunoabsorbent followed by elution with 0·12 M citrate buffer at pH 3·0. The antilymphocyte activity of eluates was studied in vitro by determination of membrane immunofluorescence titres and in vivo by the neutralization of the local renal xenogeneic graft-versus-host reaction. These tests showed that an IgG eluate of a rabbit antilymphocyte serum was nineteen times more active than the same weight of the whole IgG present in the parent serum.

Mechanism of graft-versus-host-induced lymphadenopathy in mice. Trapping vs. proliferation

Graft-vs.-host (GVH)-induced lymphadenopathy of the popliteal lymph node has been produced in C57BL/6 x A/J F(1) (BAF(1)) mice by injecting A/J spleen cells into the rear footpads. By giving (51)Cr-labeled BAF(1) lymphoid cells intravenously to the hosts, 24 h before sacrifice, we have demonstrated that a large portion of the GVH-induced lymphadenopathy is due to the trapping of circuating lymphocytes in the challenged lymph nodes. Most of the remaining enlargement can be attributed to proliferation of host cells within the reacting lymph nodes. Conditions have been defined under which the weights and [(14)C]thymidine incorporation of the popliteal nodes can be plotted against the dose of injected A/J spleen cells on a double-log scale to give a linear dose-response. The popliteal lymph node GVH assay is a simple and effective means of quantitating immune reactivity to histocompatibility antigens in mice.

Deficit of specific thymus-dependent lymphocytes in transplantation tolerance in the rat

Recovery from adoptively terminated transplantation tolerance was studied by utilizing formerly tolerant rats as donors of lymphocytes in local renal graft-vs.-host reactions (GVHR). The origin of the proliferating lymphocytes in the GVHR was studied by means of sex chromosome markers. A deficit of specifically reactive lymphocytes, while tolerance was in effect, was revealed by the continuing absence of autochthonous specifically reactive cells after tolerance was abolished in adult thymectomized chimeras. The findings are consistent with Burnet's hypothesis of the cellular basis of tolerance, but apply only to the T lymphocytes of donor origin which normally proliferate in these GVHR.

The host cell response in the local graft-versus-host reaction induced in the kidneys of F 1 rats by parental thoracic duct lymphocytes

Radioautographs of infiltrative cells in the kidneys of (Lewis x BN)F(1) rats labeled with tritiated thymidine (TdR(3)H) before the subcapsular injection of parental (Lewis) thoracic duct lymphocytes (TDL) showed a predominantly host-proliferative response by 4 days after grafting. The immediate renal incorporation of TdR(3)H was used to measure the local graft-vs.-host (GVH) reactions. Substantial reactions could still be induced in the face of the considerable degree of leukopenia after 400 R whole body gamma-irradiation. These results suggest that radioresistant cells are capable of carrying on the appropriate host activities and that the weakness of GVH reactions induced after higher doses of irradiation may be due to impairment of the mitotic mechanism of host cells. The importance of circulating leukocytes as a source of immunogenic stimulation was nevertheless substantiated by inducing local GVH reactions with Lew TDL in chimeric parental-type rats that had been repopulated with F(1) bone marrow. This result also emphasizes the nonspecific nature of tissue destruction in the renal GVH reaction in confirmation of Elkins. In this and other situations in which B cells were the predominant F(1) type elements available for interaction with parental-type TDL the reactions were nearly equivalent or equivalent to those in the appropriate controls. Typical local GVH reactions could be induced in heavily irradiated hosts by an inoculum of combined parental and F(1)-type TDL in the apparent absence of mononuclear phagocytes. The possible relationship between the activation of host lymphocytes, the involvement of B cells, and the nonspecific nature of tissue damage in the renal GVH is discussed.

Thymus origin of lymphocytes reacting and stimulating reaction in mixed lymphocyte cultures--studies in the rat

Mixed lymphocyte cultures between pairs of allogeneic cell suspensions from rat thymus of one strain versus thymus, lymph node, spleen or bone marrow from a histo-incompatible strain, have shown a decreasing gradient of stimulation capacity. After complete neonatal thymectomy 6 weeks previously, lymph-node lymphocytes are shown to have diminished or absent capacity to stimulate allogeneic rat thymocytes in mixed culture. It it concluded that thymus-derived lymphocytes appear to be required both for stimulation as well as for reaction in the mixed lymphocyte test.

Synergy among lymphoid cells mediating the graft-versus-host response. 3. Evidence for interaction between two types of thymus-derived cells

Two types of thymus-derived (T) lymphocytes have been shown to cooperate in the induction of graft-versus-host responses. One cell type is found in highest concentrations in the peripheral blood and lymph node, is extremely sensitive to anti-thymocyte serum (ATS) in vivo, and is probably part of the recirculating lymphoid cell pool (3). The second cell type, found in highest concentrations in the thymus and spleen, is relatively resistant to small doses of ATS in vivo. Both cell types are substantially depleted after neonatal thymectomy. Moreover, since synergism was also obtained using appropriate mixtures of cells from either parental strain in F(1) hosts, it was possible to show that the nonrecirculating cells determined the specificity of the response and were probably the precursors of effector cells in this response. The recirculating T cell appeared to amplify this response. The implications of these data are discussed.

Cellular receptors. effect of anti-alloantiserum on the recognition of transplantation antigens

The possibility that a rat alloantiserum DA anti-Lewis possesses similar recognition structures for Lewis transplantation antigens, as do DA immunocompetent cells, was investigated by raising an antiserum against this alloantiserum in (Lewis x DA)F(1) hosts. This antiserum, as well as one provoked by injecting DA lymphoid cells, was active against recognition structures for Lewis antigens of DA immunocompetent cells. The anti-(DA anti-Lewis) antiserum displayed the same degree of specificity as was found previously for anti-recognition structure sera prepared by injecting parental strain lymphoid cells into F(1) hosts. Since the activities of antisera raised against cell-bound receptors or against the antigen-binding region of an immunoglobulin were indistinguishable, it was concluded that the functional part of cell-associated receptors might be structurally similar to the variable portion of an immunoglobulin.

Controlled study of autoimmunization against liver in inbred rat strains

By prolonged immunization of an inbred rat strain with isologous liver homogenate in Freund's complete adjuvant a low grade autoimmune ;cholangitis' with periductular fibrosis has been demonstrated. The lesion could be transferred to isogeneic animals by serial spleen cell injections and was associated with mild but variable delayed skin sensitivity to a supernatant fraction of the liver homogenate. It is thought to be due to a combined cellular and antibody-mediated immune response, directed against bile duct constituents. Pulmonary (peribronchial) lesions have also been described in the same animals and are considered to be of similar origin and to represent a cross reaction with tissue of similar embryological (entodermal) origin. This appears to be the first description of periductular hepatic fibrosis clearly resulting from an autoimmune reaction and may provide a model for further study of rather similar histological reactions known to occur in man.

The factor of immunization in the rat. The effect of allogeneic immunization on graft-versus-host activity

Using a popliteal lymph node weight assay the graft-versus-host activity of lymphocytes from donors immunized with allogeneic tissue has been assayed by comparison with that of lymphocytes from nonimmune donors. When the donors were immunized against weak histocompatibility antigens (non-AgB) the specific GVH activity of its lymphocytes was increased. This increase was greater if spleen cells rather than thoracic duct lymphocytes were the source of the donor cells used for assay. The increase in GVH activity was also greater if the standard immunization procedure of two successive skin allografts was followed by three boosting injections of allogeneic lymphoid cells. When donors were immunized against strong histocompatibility antigens the specific GVH activity of the donors' lymphocytes was slightly increased, was unchanged, or was actually decreased depending on the experimental situation. In donors rendered incapable of a humoral alloantibody response by whole body X-irradiation, immunization across a strong barrier was followed by little or no increase in the specific GVH activity of TDL. In the rat, as in other species, the increase in GVH activity after immunization is inversely proportional to the strength of the antigenic barrier involved.

Response of rat blood, spleen, and lymph node leucocytes to soluble and insoluble antigen

Solubilized sheep erythrocyte stroma was found to be antigenic in rats. Spleen and lymph nodes of rats injected with this antigen contained more 7S than 19S plaque-forming cells throughout the primary and secondary responses. When compared to the primary response, secondary immunization with this antigen elicited increased numbers of both 19S and 7S plaque-forming cells. Antibody synthesizing leucocytes in the blood during the primary and secondary responses were predominantly 7S producers during the first few days. Later 19S producers predominated.

Intact sheep erythrocytes elicited the same pattern of 19S and 7S antibody-forming cell development in the lymph nodes and blood of intravenously injected rats, but during the early primary response in the spleen there was a predominance of 19S over 7S plaque-forming cells. The 7S cells were in a majority during the entire secondary response of the spleen to intact erythrocytes. The secondary response of spleen and lymph node to intact erythrocytes showed an elevated 7S plaque forming cell response but the number of 19S cells was similar to that detecred after primary immunization.

The appearance of haemolytic and haemagglutinating 19S and 7S antibody to sheep erythrocytes or solubilized stroma generally reflected the cellular picture of the spleen. By using an anti-7S globulin it was found that 19S and 7S antibody appeared simultaneously in the serum.

After immunization of rats with intact erythrocytes or solubilized stroma the number of lymphoid cells that took up tritiated thymidine was about one hundred-fold greater than the number of antibody-forming cells as determined by localized haemolysis in gel. The number of lymphoid cells positive in an immunocyto-adherence assay was more closely related to the number of cells taking up tritiated thymidine.

The passive transfer of spleen cells from rats immunized to sheep erythrocytes showed the number of circulating antibody-forming cells in the normal and irradiated recipients to be related to the concentration of antibody-forming cells localizing in the recipient spleen. The number of antibody-forming cells in the peripheral blood was greater in splenectomized recipients. Irradiation had no effect on the number of antibody-forming leucocytes in the circulation of the splenectomized recipients.

Synergy among lymphoid cells mediating the graft-versus-host response. II. Synergy in graft-versus-host reactions produced by Balb-c lymphoid cells of differing anatomic origin

The capacity of cells from different lymphoid tissues obtained from Balb/c mice to produce graft-vs.-host (GVH) reactions was quantitatively determined in C57BL/6N by Balb/c F(1) hybrid recipients. Synergistic responses were observed when small numbers of cells from lymphoid tissues that were rich in GVH activity such as spleen and femoral lymph node were combined with weakly reactive thymus cells. Thymus and spleen cells obtained from 1-wk old mice were separately inactive but produced moderate GVH reactions when combined in equal proportions. GVH activity of spleen cells from mice thymectomized at 3 days of age was partially restored by the addition of small numbers of spleen or thymus cells from adult mice. Changes in ratio between the two cell populations markedly affected the degree of synergy. Synergy was not observed when Balb/c cells were combined with Balb/c x C57BL/6N F(1) hybrid cells and inoculated into C57BL/6N recipients, but was demonstrated when Balb/c and C57BL/6N cells were combined and inoculated into F(1) recipients, indicating that a genetic disposition to mount GVH reactions in both populations is required to produce synergy. The data indicate that at least two cell types are necessary for GVH reactions, and that synergy between cell populations results from favorable adjustments in the ratio between these two cell types.