Syngeneic Lymph Node Cells Research Articles

Effect of Seliciclib (CYC202, R-Roscovitine) on Lymphocyte Alloreactivity and Acute Kidney Allograft Rejection in Rat

T cell stimulation by alloantigens is followed by cell cycle progression, an event that is critically dependent on cyclin-dependent kinases. We conducted a study to evaluate whether the cyclin-dependent kinase inhibitor seliciclib affected rat lymph node cells (LNc) activation and proliferation induced by either concanavalin A or allogeneic splenocytes in vitro and studied the mechanisms underlying the suppressive effect. We also investigated the immunosuppressive properties of seliciclib in vivo. Seliciclib completely inhibited in vitro proliferation of LNc and CD8 T cells, in response to either concanavalin A or allogeneic splenocytes. The percentage of activated LNc was lower in mixed leukocyte reactions (MLR) added with seliciclib than in MLR added with vehicle. The percentages of viable and apoptotic cells at the end of MLR with seliciclib were comparable to those of MLR with vehicle. LNc pre-exposed in MLR to seliciclib did not respond to further stimulation with alloantigens, and neither IL-2 nor IL-15 restored proliferation. These data indicate that the inhibitory effect of seliciclib on T cell alloreactivity is not because of cytotoxic effect but is associated with induction of profound T cell anergy. LNc harvested at the end of the primary MLR with seliciclib did not suppress the proliferation of syngeneic LNc cells toward allogeneic splenocytes, thus excluding that seliciclib induced the formation of regulatory cells. Finally, seliciclib partially prolonged grafted animal survival in a rat model of fully major histocompatibility complex-mismatched kidney transplantation. Altogether these results document that seliciclib regulates lymphocyte reactivity and may exert an immunosuppressive effect in vivo in the setting of transplantation.

Peripheral tolerance induced in lymph nodes by syngenic spleen cells inhibits generation of CTLs to hapten-altered self antigens but not to alloantigens

The immunological tolerance that is induced in lymph nodes that have been exposed to syngeneic spleen cells has been examined. Development of cytotoxic T lymphocytes was used to assess the immunological status of the lymph node cells. The tolerance was studied from the viewpoint of its induction, its activation, and its specificity. We had already reported that injecting either T or B cells of splenic origin into a regional lymph node environment a week prior to immunization for CTL to hapten-altered self antigens prevents development of the CTL. Here, we confirm that syngeneic splenic cells but not lymph node cells will induce the suppression provided that spleen cells are not coupled with hapten. We now report that splenic cells that cannot replicate or synthesize and secrete protein are capable of inducing the suppression. The data suggest a preformed surface marker peculiar to spleen cells and perhaps on cells that traverse the thymus induces local tolerance that is mediated by suppressor cells. Triggering the induced suppressor T cells (previously identified as CD8 +) was achieved by syngeneic spleen cells as well as by H-2-compatible, Mls-disparate spleen cells but not by syngeneic lymph node cells or apparently by allogeneic spleen cells. Furthermore, triggering suppression was achieved by hapten-coupled syngeneic spleen cells whereas such cells would not induce the suppression. Thus, activating the suppressor cells requires reexposure to splenic cells of the proper MHC haplotype, unaltered or coupled with either TNP or FITC. Once triggered, the suppression was manifested toward CTL generation against hapten-coupled syngeneic antigens on either spleen or lymph node cells but not against allogeneic antigens. Thus, the specificity of the tolerance was directed to altered self antigens despite its induction by unaltered spleen antigen. Furthermore, for suppression to be seen the spleen antigen was not required to be on the hapten-coupled syngeneic cells used for the CTL immunization. The relationship of the splenic cell “antigen” to hapten-altered self antigens and to other surface markers and its site of acquisition within the body and its significance for cell homing have become intriguing questions of importance. This information has been discussed from the viewpoint of its applicability to autoimmune diseases as well as to cessation of inflammatory reactions that may be mediated by lymph node cells.

Popliteal lymph node reactions in mice induced by the drug zimeldine

The antidepressant drug zimeldine was screened for immune modulating properties using the popliteal lymph node (PLN) assay as a test system in mice. In immunocompetent as well as congenitally athymic nude mice, footpad injection of 1.0 mg zimeldine triggered a bimodal footswelling. A transient oedematous swelling, histologically characterized by mast cell degranulation, was followed by infiltration of polymorphnuclear cells. A dose-dependent PLN enlargement to the agent was observed, which appeared to be more pronounced in immunocompetent mice as compared with athymic nude mice, and in H-2 b mice as compared with H-2 d mice. After injection of 1.0 mg zimeldine into the footpad of C57BL/10 mice, significant enlargement was already observed by 3 days after injection, was optimal around day 9 and persisted for at least 30 days. Histologically, PLN reactions were characterized by blast transformation of lymphocytes and expansion of paracortical areas prior to germinal center reactions in enlarged follicles. Size of both areas gradually decreased as the medulla filled with plasma cells, 7–30 days after injection. The observed reactions could not be transferred with syngeneic lymph node cells after prior exposition to zimeldine in vivo or in vitro. We conclude that zimeldine induces strong and persistent PLN enlargement, blastogenesis and prominent germinal center reactions. Immunocompetent T-cells are apparently conducive, but not preprequisite to these reactions, which suggests involvement of multiple mechanisms including those mediated by inflammatory reactions in the foot. It is unlikely that the observed enlargement of PLN can be attributed to a direct chemical modification of leukocyte membranes by zimeldine. The protracted nature of the reaction may indicate that zimeldine somehow interferes with inhibitory feedback mechanisms.

Suppression of clinical signs of cell-transferred experimental allergic encephalomyelitis and altered cerebrovascular permeability in Lewis rats treated with a plasminogen activator inhibitor

The purpose of this study was to determine whether fibrinolysis resulting from activation of the clotting cascade in juxtaposition to endothelial cells of the central nervous system (CNS) microvasculature is important for development of clinical signs of experimental allergic encephalomyelitis (EAE) in recipient Lewis rats. Rats were injected with previously primed syngeneic lymph node cells, activated in vitro with guinea pig myelin basic protein, and subsequently treated daily with trans-4-(aminomethyl)cyclohexanecarboxylic acid (AMCA), a synthetic inhibitor of plasminogen activator. Clinical signs of EAE were significantly suppressed in AMCA-treated rats compared to saline-treated control recipient animals. Furthermore, suppression of clinical signs in AMCA-treated rats was accompanied by a significant curtailment in EAE-associated increased permeability of the blood-brain barrier (BBB). These findings provide evidence that CNS-associated deposition of fibrin and ensuing fibrinolysis, together with increased permeability of the BBB, are related prerequisite events for expression of clinical manifestations of EAE.

The role of dendritic cells in the initiation of immune responses to contact sensitizers: I. In vivo exposure to antigen

Twenty-four hours after skin painting mice with picryl chloride (PIC) there was a four- to fivefold increase in the numbers of dendritic cells (DC) isolated from the lymph nodes. These DC initiated primary proliferative and cytotoxic responses when added to cultures of normal syngeneic lymph node cells. The proliferative response was enhanced when the donors of the responding lymph node cells were sensitized with the same antigen. Contact sensitivity developed in syngeneic mice injected into the footpads with 30,000–50,000 DC from lymph nodes of mice painted with picryl chloride 1 day previously. Thus, 1 day after skin painting mice, there were dendritic cells in the draining lymph nodes which were able both to initiate primary stimulation of lymphocytes in vitro and to sensitize recipient mice to give specific delayed hypersensitivity reactions.

The cellular basis of allograft rejection in vivo. III. Restoration of first-set rejection of heart grafts by T helper cells in irradiated rats.

An adoptive transfer model was used to examine the subpopulations of lymphocytes required to effect first-set rejection of directly vascularized heart allografts. PVG heart grafts are not rejected in irradiated DA hosts for at least 50 days. The adoptive transfer of 5 X 10(7) syngeneic lymph node cells (LNC) restores rejection to 14.4 +/- 2.4 days (mean +/- SD). Subpopulations of LNC, were separated by an indirect "panning" technique using the mouse antirat monoclonal antibodies W3/13, MRC OX8, or W3/25 to deplete the unwanted subsets of cells. Each subpopulation was tested, in a number equivalent to the number present in 5 X 10(7) normal LNC, for its ability to cause the rejection of heart grafts. Whole T cells (W3/13+) or helper/inducer T cells (W3/25+) restored graft rejection to 16.4 +/- 3.8 d and 16.0 +/- 2.4 days, respectively. Neither cytotoxic/suppressor T cells (MRC OX8+) nor B cells (Ig+) restored rejection. Indirect immunoperoxidase stains of the grafts showed that although W3/25+ cells predominated in the rejected tissue, MRC OX8+ cells were also present even in grafts from rats restored with inocula that contained less than 1% MRC OX8+ cells. Examination of lymphoid tissues suggested that the MRC OX8+ cells might be of host origin. By the time the grafts were rejected in irradiated hosts, significant thymic regeneration had occurred and there were large numbers of MRC OX8+ cells present in the thymus, as well as some in lymph nodes and spleen.

Immune Responses to Mouse Neuroblastoma C1300

A 51Cr microcytotoxicity assay was used to study the kinetics of lymph-node- and spleen-cell-mediated cytotoxicity of A/JAX hosts following a single inoculum of the in vivo grown syngeneic neuroblastoma C1300. Lymph node cells (LNCs) demonstrated cytotoxicity which peaked at day 9, decreased as the tumor approached the 0.5-gram weight and increased again as the tumors grew. The increase in cytotoxicity following the depressed state was significantly greater than the initial peak, particularly in those mice bearing large tumors. Three groups of A/JAX mice were evaluated: mice receiving tumor cells alone; mice that were either thymectomized or splenectomized prior to inoculation, and mice that rejected the tumor. The C57Bl/6 served as an allogeneic comparison. Significant cytotoxicity was detected earlier with allogeneic LNCs than with spleen cells. Thymectomy and splenectomy elicited syngeneic LNC immune responses below or equal to the level found in nonimmune A/JAX hosts.

Natural regulatory cells in murine bone marrow: inhibition of in vitro proliferative and cytotoxic responses to alloantigens.

A lymphocyte-enriched fraction of murine bone marrow (BML), obtained by sucrose density fractionation, contains natural regulatory cells that can profoundly suppress the proliferative and cytotoxic response of syngeneic lymph node cells to irradiated alloantigens in a mixed lymphocyte culture (MLC). A close correlation exists between the inhibition of alloantigen-induced proliferation and the generation of cytotoxic effectors. The suppression of proliferation is dependent on the dose of BML added to the cultures but is not due to cell crowding, since red blood cells, thymocytes, and irradiated splenocytes, all syngeneic to the lymph node responders, do not inhibit proliferation to the degree observed with BML. The addition of BML to cultures does not cause the maximum proliferative response to change from the usual day 5 peak, indicating that there is no change in culture kinetics. The release of nonradioactive thymidine by BML cannot explain the suppression. The target of suppression is maximally affected during the first 24 hr of culture, since adding BML to MLC later than this resulted in negligible inhibition of proliferation. Thus, the natural regulatory cell-mediated suppression reflects inhibition of "early" events in the proliferative response to alloantigens.

Soluble Helper Factor(s) Participates in the Generation of Cell Mediated Cytotoxicity Directed against Syngeneic Tumor Cells

Abstract Data presented here suggest that one mechanism by which cytotoxic T lymphocytes are generated against certain syngeneic tumors may involve collaboration between pre-killer T cells and helper T cells via a soluble helper factor. Furthermore both lymphocyte-defined as well as cytotoxicity-defined antigens expressed on tumor cells may be involved in stimulating the generation of specific cytotoxic T cells. A lymphoma cell line (CH-1) derived from an SJL mouse stimulates both a syngeneic proliferative and cytotoxic response. However, heattreatment of the CH-1 cells, which is known to functionally inactivate lymphocyte-defined antigens, reduced significantly the ability of such cells to stimulate proliferation and the generation of cytotoxic T cells. The addition of supernatant fluids from either mixed lymphocyte cultures or from cultures in which syngeneic lymph node cells were sensitized against CH-1 tumor cells, restored the ability of heat-treated tumor cells to stimulate a full syngeneic cytotoxic response. The degree of T cell specific cytotoxicity that was generated was dependent in part on the concentration of helper factor(s) added to the cultures. Furthermore, supernatant fluids containing helper activity were not able to stimulate responder cell cytotoxicity in the absence of heat-treated CH-1 cells. The helper activity, detected in cultures where SJL lymph node cells were stimulated by CH-1 cells, appears to be similar to that present in supernates from allogeneic MLC since neither are antigen specific nor H-2 restricted in their ability to assist in the development of cytotoxic T cells.

Cytotoxic T cell responses to a syngeneic tumour: conditions for primary activation in vitro and biological activity in vivo.

In vitro T cell activation against alloantigens requires antigen presentation to the responsive cell in combination with an inductive signal, termed the lymphocyte costimulator. This inductive signal can be provided by allogeneic stimulator cells or can be provided exogenously using the supernatant from Con A-activated spleen cells (CS) as a source of the costimulator (1,2). Unlike responses to alloantigens, cocultivation of the P815 tumour of DBA/2 mice with syngeneic lymph node cells results in the generation of little cytotoxic activity which is detected only at high effector to target cell ratios and after long incubation times (3,4). We have recently reported that the addition of CS to in vitro cultures allows significant cytotoxic T cell activation of DBA/2 lymphocytes to the syngeneic tumour P815 (5). In this report the requirement for CS in the generation of P815 reactive cells is further characterized and preliminary studies on the biological effectiveness of these activated cells in controlling the growth of P815 in DBA/2 mice are presented.KeywordsSpleen CellCytotoxic ResponseResponsive CellSyngeneic TumourAustralia IntroductionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Amplification of the proliferative response to alloantigen by a factor present in an extract of syngeneic thymic lymphoid cells.

A synergistic interaction in the proliferative response to alloantigen has been previously noted when intact thymus cells are cultured with post-thymic (peripheral) lymphoid cells. In the present study, a factor extracted from the thymus has been shown to similarly enhance the reactivity of syngeneic lymph node cells and thus to retain the amplifier activity of intact thymus cells. The factor has no effect on lymphoid cell proliferation in the absence of alloantigen. Cells with amplifier activity are found in highest concentration in the thymus but also may be detected in spleen cells that are nonadherent to nylon wool. The factor is shown in these experiments to be derived from thymic lymphoid cells and to act primarily upon post-thymic (peripheral) lymphoid cells. As such, this factor appears to be distinct from various other thymus factors that have been localized to thymic reticuloepithelial elements and that are thought to effect predominantly the differentiation of T-cell precursors.

SUPPRESSION OF THE IN VIVO HUMORAL AND CELLULAR IMMUNE RESPONSE BY STAPHYLOCOCCAL ENTEROTOXIN B (SEB)

SUMMARY In vitro blast transformation of mouse spleen and lymph node cells occurs in response to staphylococcal enterotoxin B (SEB), as measured by 3H-thymidine incorporation. This response appears to be similar to the stimulation by phytohaemagglutinin. Treatment with SEB immediately after skin grafting suppressed a first, but not a second-set allograft rejection in mice. Syngeneic lymph node cells stimulated in vitro by SEB and adoptively transferred to normal mice failed to transfer suppression of graft rejection. Immediate injection of SEB following immunization with sheep red blood cells exhibited a markedly suppressed plaque-forming and rosette-forming cell response, whereas no suppression of the antibody response to a thymus-indendent antigen Escherichia coli lipopolysaccharide, was observed. Introduction of SEB after the second immunization with sheep red blood cells showed no significant suppression effect in plaque formation. Formalinized or heat-treated SEB destroyed the mitogenic and immunosuppressive capability as tested by 3H-thymidine incorporation, skin rejection, and plaque formation. It is suggested that the mechanism of this immunosuppression involved the interaction of SEB with T cells, which in some manner block T cell function in the early recognition stage, probably through nonspecific mitogenic activity.

Effect of insulin and its derivatives on incorporation of [1-14C]glycine into tissue proteins

Lethally irradiated DBA/l mice or (C57Bl X DBA/l1 F1 hybrid mice were injected with therapeutically effective doses of isologous bone marrow cells; simultaneously syngeneic lymph node cells from either intact (control) animals or mice survived after sublethal irradiation were transplanted. In control the viability of the recipients was not affected by the presence of lymphoid cells in the mixed transplant. In contrast, the beneficial action of the bone marrow cells was abolished (killing-effect) by the lymphoid cells from mice sacrificed 6 to 12 months after the irradiation (600--700 r). The manifestation of the killing-effect depended on the number of the transplanted lymphoid cells and on the dose of the bone marrow cells in the transplant. The killing-effect was not revealed when the lymphoid cells were obtained from the donors on the 30th day after irradiation. The results suggest the autosensitization of the organism at the late postirradiation periods.

Cell-cell interactions in blast transformation of rat lymphocytes by neuraminidase and galactose oxidase

Optimal reaction conditions for the in vitro blast transformation of rat lymph node cells (LNC) by neuraminidase (N) and galactose oxidase (GO) were determined. Treatment with either enzyme alone, or with GO before N, did not produce significant stimulation. The kinetics and magnitude of the response to NGO, as measured by [ 3H]TdR incorporation, were compared with those induced by periodate treatment and by concanavalin A (ConA). Rat LNC treated with NGO (but blocked by mitomycin C) caused blast transformation of untreated syngeneic LNC. The magnitude of this indirect response was about one-quarter of that attained for NGO-treated LNC, and the kinetics were somewhat slower. Supernatants from cultures of NGO-stimulated cells were not able to activate untreated cells, and, using Marbrook culture vessels, no evidence was found for the release of soluble factors that could either activate untreated cells or enhance the magnitude of indirect stimulation. Indirect stimulation, therefore, appears to require cell-cell contact. A second kind of cellular interaction was observed in experiments in which NGO-treated LNC were cultured at different cell densities in the presence or absence of mitomycin C-blocked filler LNC. In the absence of filler cells, the incorporation of [ 3H]TdR was a linear function of the number of NGO-treated cells in each culture over a wide range of cell densities. However, if filler cells were present, [ 3H]TdR-incorporation was substantially enhanced. Thus the filler cell population contains cells that assist or potentiate the blast response to NGO, probably by increasing the number of lymphocytes that are stimulated.

In vitro induction of immunological memory against testicular autoantigens.

It has been shown that normal rat lymph node cells can be autosensitized in vitro against dissociated testis cells from the same donor animal. The present study was undertaken to demonstrate that self-responsive activated lymphocytes can revert back to quiescent small secondary lymphocytes and that immunological memory can be induced in vitro against the autoantigens. Injection of lymphoblasts raised in mixed cultures of fresh lymphocytes and autologous trypsin-dissociated testis cells can induce progressive orchitis. It was found that L.BDV secondary lymphocytes primed against autologous testis cells responded strongly when exposed to syngenic L.BDV testis cells but failed to react against allogenic Lewis testis cells thus demonstrating the immune specificity of the autosensitized secondary EAO lymphocytes. These findings combined with other data suggest that major histocompatible gene complex autoantigens are recognized in the secondary reaction. 2 degree EAO lymphocytes however were restimulated not only by syngeneic testis cells but also to an even greater extent by syngeneic lymph node cells whereas fibroblasts did not exhibit such a response. Possible explanations of the nature of the autoantigens that elicit the secondary EAO reaction are discussed. This autoimmune memory system is proposed as a model for the study of the physiological mechanisms responsible for self-tolerance at the T cell level.

Periodate and concanavalin A induce blast transformation of rat lymphocytes by an indirect mechanism.

When rat lymph node cells, rendered incapable of division by treatment with mitomycin C, were then reacted with sodium metaperiodate (NaIO4), they stimulated the transformation of untreated, syngeneic lymph node cells in vitro. Unequivocal evidence that untreated lymph node cells responded in this situation was obtained by means of sex chromosome karyotype analysis. In experiments in which the ratio of responder to stimulator cells was varied between the limits of pure responder and pure stimulator cells at a constant cell density, [3H]thymidine incorporation increased linearly to a maximum at a ratio of 1:1, and then decreased linearly. These results suggest a predominantly bicellular reaction in which one periodate-treated cell stimulates only one responder cell. In experiments in which stimulator cells were reacted with periodate, but not treated with mitomycin C, and then mixed at a 1:1 ratio with untreated, syngeneic lymph node cells, karyotype analysis showed that both periodate-treated and untreated lymph node cells responded in significant numbers. Lymph node cells were cultured at various cell densities under three different conditions: one group was made up entirely of cells treated with periodate; a second group consisted of a 1:1 mixture of cells treated with periodate and untreated cells; the third group contained normal cells cultured in the presence of soluble concanavalin A. Expressed as [3H]thymidine incorporated per 10(6) cells, a progressive increase was found at the lower cell densities for all three groups, and identical slopes (about 2.5) were obtained when the results were plotted on a full logarithmic scale. Mitomycin C-treated lymph node cells incubated with concanavalin A and then thoroughly washed were found to be capable of transforming untreated, syngeneic lymph node cells. Maximal [3H]thymidine incorporation also occurred at a ratio of 1:1. These results show that, similarly to periodate stimulation, mitogenic stimulation by concanavalin A probably operates through an indirect mechanism, analogous to a mixed lymphocyte reaction. It is possible that other mitogenic agents also operate indirectly.

Stimulation of syngeneic and allogeneic lymphoid cells by tumour cells in vitro.

August and Wistar rat lymph node cells were found to respond well to PHA stimulation and in mixed lymphocyte culture, as determined by an increased incorporation of 3H-thymidine. August rat lymph node cells were also stimulated by incubation with irradiated syngeneic tumour cells. Allogeneic Wistar rat lymph node cells produced a larger response to the August tumour cells. The response of syngeneic and allogeneic lymph node cells was reduced by pretreating the tumour cells with a Wistar anti-tumour serum. Pretreating the tumour cells with sera from normal or tumour bearing rats also reduced the response of syngeneic lymph node cells but did not reduce the response of allogeneic lymph node cells.

On the influence of neuraminidase on casein-induced amyloidosis in C 3 H mice.

Intraperitoneal inoculation of the receptor‐destroying enzyme neuraminidase had little effect on spleen amyloid development in mice during caseination. However, incubation of normal syngeneic lymph node cells with neuraminidase before they were injected into mice during casein treatment significantly enhanced the amyloid‐promoting effect of the cells. It is suggested that neuraminidase‐treated lymph node cells may be preferentially trapped in the spleen with subsequent transfer of an amyloid component to macrophages. The polycation DEAE‐dextran, known to accelerate amyloid formation if given intraperitoneally with casein, did not influence the effect of cell transfer. This may indicate that the amyloid promoting mechanisms of the two membrane‐active substances are different.

RNA in the periphery of rapidly proliferating mouse lymphoid cells.

AbstractRNA in the peripheries of various populations of lymph node cells (LNC) has been evaluated by measuring the electrophoretic mobilities of cells, before and after treatment with active or inactivated ribonucleases. Three different populations of LNC were studied: (1) “resting” normal age control LNC; (2) “syngeneic” LNC from irradiated (C3H × C57BL)F1 or C3H mice four to six days following transplantation of syngeneic spleen cells; such cells were progeny of lymphopoietic progenitor cells of the spleen; and (3) “allogeneic” LNC from irradiated (C3H × C57BL)F1 mice four to six days after grafting C3H (parental) spleen cells; such cells were progeny of lymphopoietic progenitor cells, but also alloantigen‐sensitive cells of the spleen which proliferate in response to the host's alloantigens (a “graft‐versus‐host” immunological reaction). Whereas the normal LNC had no detectable peripheral RNA, the allogeneic and syngeneic LNC did, i.e., ribonuclease reduced their mean electrophoretic mobilities by 13.6 and 9.2 per cent, respectively. Since both allogeneic and syngeneic LNC had peripheral RNA, no specific correlation could be made with immunological activity. 3H‐uridine and 14C‐thymidine incorporation into lymph nodes was greatest in allogeneic, intermediate in syngeneic and least in age control lymph nodes, indicating a “population shift” in the spleen cell chimeras toward relatively immature, rapidly proliferating cells, which had a relatively high rate of RNA synthesis. Thus, rapidly proliferating lymphoid cells do have RNA in their peripheries, but its relation to specific immunological function has yet to be ascertained.

Delayed mortality after mid-lethal exposures to wholebody irradiation and its modification by treatment with syngeneic lymph-node or bone-marrow cells.

SummaryDeaths between 25 and 275 days after mid-lethal x-irradiation were closely reminiscent of the ‘secondary disease’ of supralethally irradiated mice given allogeneic or xenogeneic cells. One-third of the mice with the diarrhoea syndrome died of it; the majority recovered spontaneously.The delayed mortality was prevented and diarrhoea minimized by treatment with 107 syngeneic lymph-node cells either soon after irradiation or 22 days later. Thus death from lymphoid insufficiency is a specific consequence of whole-body irradiation by mid-lethal doses. Radiation-induced somatic mutation in surviving cells may play a part.Early treatment with 5 × 106 syngeneic bone-marrow cells was also effective. Bone marrow at 22 days had less effect on diarrhoea and did not decrease mortality but changed the post-mortem findings, death occurring characteristically with markedly congested lungs and with amyloid deposits in spleen and liver.Body weight was increased but not restored to normal by treatment with either kin...