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Biomedical subjects

E Holler

Publications and source records attributed to E Holler.

At least 73 records · Page 4Linked to original sources
PubMed1997

Adoptive immunotherapy in canine chimeras.

Chimerism and tolerance after bone marrow transplantation provide excellent conditions for adoptive immunotherapy with T cells of the marrow donor. We studied adoptive immunotherapy in dog leukocyte antigen-identical canine littermate chimeras. Mixed chimeras were produced by conditioning treatment with total body irradiation of a dose of 10 Gy, a uniformly lethal dose in dogs, and infusion of between 1 x 10(8) and 2 x 10(8)/kg mononuclear marrow cells treated with absorbed antithymocyte globulin for inactivation of T cells. Donors were of opposite sex. Persistent mixed chimerism was induced in six of nine dogs, chimerism was complete in one dog, and only transient in two dogs. Tolerance to donor skin grafts was demonstrated in eight dogs, including a dog without cytogenetic evidence of chimerism. Lymphocytes of the marrow donor (between 3.2 x 10(8)/kg and 4.1 x 10(8)/kg) were transfused at various times after transplantation. Nontransfused dogs survived without graft-versus-host disease (GVHD), whereas dogs transfused on days 1 and 2 and dogs transfused on days 21 and 22 developed GVHD and died. In contrast, dogs transfused on days 61 and 62 or later survived without GVHD. Chimerism converted from mixed to complete in six of six transfused dogs and in one of eight nontransfused dogs (P<0.005). Donor lymphocyte transfusions 2 years and 4.5 years after transplantation induced split chimerism with lymphoid cells of donor origin and myeloid cells of host origin in one dog and complete chimerism in the other dog. Before lymphocyte collection, donors were immunized against tetanus toxin. Seven days after lymphocyte transfusion, recipients were given booster injections of tetanus toxoid and primary immunization against diphtheria toxin. In transfused animals, antibody titers against tetanus were demonstrated already before the booster injection. Transfused animals developed higher titers of antibody against tetanus and diphtheria toxin than nontransfused animals. Donor lymphocytes converted mixed chimerism into complete chimerism without producing GVHD, when the transfusion was delayed for 2 months or later after transplantation. Transfusion of donor lymphocytes transferred immune reactivity against tetanus toxin and improved reactivity against diphtheria toxin as a new antigen.

Animals↗
PubMed1997

Hematopoietic transplantation: state of the art.

Bone marrow transplantation has developed from an experimental therapy for a small group of patients to a well-established form of treatment with well-defined indications for a large group of patients with hematological and non-hematological neoplasia. The availability of suitable donors has more than doubled due to large registries of persons volunteering for marrow donation. With improved techniques for histocompatibility typing, it has become possible to study the role of specific histoincompatibilities for graft-versus-host disease and graft-versus-leukemia reactions. The source of hematopoietic stem cells now comprises not only bone marrow, but also stem cells mobilized into the peripheral blood and stem cells from cord blood. Hematopoietic growth factors have found a large distribution in the mobilization of stem cells and support for hematological reconstitution. They are studied for the expansion of pools of stem cells. Reconstitution of antileukemia and antiviral activity has been achieved by adoptive immunotherapy using lymphocytes and dendritic cells cultured in vitro. The way from transplantation of bone marrow to cellular and genetic engineering leads to new indications such as treatment of severe autoimmune disease. Hematopoietic transplantation has come a long way and it still has possible new areas of application.

Graft vs Host Disease↗
PubMed1997

Laboratory markers of veno-occlusive disease in the course of bone marrow and subsequent liver transplantation.

Plasminogen activator inhibitor 1 (PAI-1) and amino-propeptide of type III procollagen (PIIINP) have been described as markers of hepatic veno-occlusive disease (VOD) after bone marrow transplantation (BMT). We determined these parameters in two patients undergoing BMT and subsequent liver transplantation due to VOD. Previously normal PAI-1 levels (maximum 30.0 ng/ml in patient 1, 23.7 ng/ml in patient 2) were elevated for the first time in both patients at the time of clinically diagnosed VOD on days 40 and 20, respectively (patient 1: 317.5 ng/ml; patient 2: 317.2 ng/ml). Levels remained elevated until liver transplantation was performed on days 79 and 41, respectively. Baseline levels (day -8) of aminopropeptide of type III collagen (patient 1: 4.44 microg/l; patient 2: 8.1 microg/l) peaked at the time of BMT in both patients (155.0 microg/l and 108.3 microg/l). After an intermittent decrease at the time of discharge on day 32, a second elevation was observed in patient 1 when she was readmitted and presented with typical signs of VOD on day 40. In patient 2, PIIINP levels remained high until VOD was diagnosed (day 20) and liver transplantation was performed. After liver transplantation, PAI-1 levels normalized in both patients and PIIINP levels declined. Both patients died due to infectious complications and multiorgan failure on days 141 and 101, respectively. Whereas the early rise of PIIINP did not correlate with the clinical onset of VOD, the results emphasise the relevance of PAI-1 for diagnosing VOD.

Acute Disease↗
PubMed1997

Endothelial cell markers in bone marrow transplant recipients with and without acute graft-versus-host disease.

To investigate endothelial cell alterations in BMT recipients developing acute graft-versus-host disease (aGVHD) we determined levels of the endothelial cell markers von Willebrand factor (VWF) and thrombomodulin (TM) in 57 patients undergoing BMT. Before conditioning VWF and TM levels did not differ significantly between transplant recipients who later developed no or mild (grade I) aGVHD (group A, allogeneic n = 22, autologous n = 7; VWF 136.0 +/- 44.1%; TM 29.5 +/- 18.0 ng/ml), and those with moderate or severe (grade II or III) aGVHD (group B, n = 28; VWF 142.2 +/- 37.6%; TM 35.2 +/- 20.1 ng/ml). A first significant rise of both VWF and TM level was noted after conditioning (day 0) both in group A (VWF 197.0 +/- 113.3%; P < 0.001; TM 39.3 +/- 23.3 ng/ml; P < 0.01) as well as in group B (VWF 201.7 +/- 53.3%; P < 0.0001; TM 43.5 +/- 23.5 ng/ml; P < 0.05). Subgroup analysis of autografted patients revealed no significant increase after conditioning in these patients. At the time of engraftment and onset of aGVHD (day 21), when VWF and TM levels within the groups were significantly elevated as compared with baseline (day -8) levels, group B patients (62.7 +/- 38.5 ng/ml) had significantly higher (P < 0.01) TM levels than patients of group A (37.4 +/- 19.6 ng/ml). This significant elevation also persisted at the end of the investigational period (day 28; group B: 56.0 +/- 37.6 ng/ml; group A: 38.2 +/- 23.7 ng/ml; P < 0.01). An elevation of endothelial cell markers is found in the course of BMT, particularly after conditioning and at the time of engraftment. This increase is pronounced in patients with aGVHD suggesting not only epithelial cell but also endothelial cell injury during aGVHD.

Acute Disease↗
PubMed1997

Differential modulation of IL-1-induced endothelial adhesion molecules and transendothelial migration of granulocytes by G-CSF.

Granulocyte colony stimulating factor (G-CSF) is widely used for mobilization of haemopoietic stem cells into the peripheral blood. However, little is known about the mechanisms involved in mobilization and the immune modulatory effects of this growth factor. In this report we show that G-CSF down-regulated intercellular adhesion molecule 1 (ICAM-1) induced by Interleukin-1 (IL-1) on human endothelial cells. Interestingly, the G-CSF-mediated down-modulation of IL-1-induced ICAM-1 appeared to be biphasic. In pharmacological concentrations (> 300 ng/ml), and in dose ranges of plasma G-CSF levels above that of nonfebrile healthy individuals (30 pg/ml), a significant decrease in surface ICAM-1 could be observed. This could be explained, at least in part, by an increased autocrine G-CSF production by endothelial cells in response to IL-1 and exogenous G-CSF. In contrast to ICAM-1, IL-1-triggered VCAM-1 expression was superinduced by G-CSF with the optimal concentration of 30 pg/ml. To evaluate the functional significance of these findings, 51Cr adhesion assays with peripheral blood mononuclear cells (PBMC) or granulocytes known to lack the VCAM-1 counter-receptor very late antigen 4 (VLA-4) and IL-1-stimulated endothelial cells, in the presence or absence of G-CSF, were performed. G-CSF could not inhibit the IL-1-induced adhesion of PBMC to endothelial cells, which may be due to the differential adhesion molecule modulation. In contrast, granulocyte adhesion induced by IL-1 could effectively be blocked by co-incubation with G-CSF. Finally, G-CSF also inhibited transendothelial migration of granulocytes through IL-1-activated endothelial cells in a concentration-dependent manner.

Cell Adhesion↗
PubMed1997

Adoptive immunotherapy with donor lymphocyte transfusions.

Adoptive immunotherapy denotes the transfer of immunocompetent cells for the treatment of leukemia, cancer, or viral disease. It has regained much interest through the success of treating recurrent leukemia after allogeneic bone marrow transplantation with the transfusion of donor lymphocytes. Chimerism and transplantation tolerance toward the donor offer the possibility of adoptive immunotherapy using donor lymphocytes. In animal studies, donor lymphocytes could be transfused into the chimeric animal, if the transfusion was delayed after marrow transplantation. Transfused lymphocytes exhibit a graft-versus-leukemia effect and increase chimerism. Immunity could be transferred and immune reactivity toward new antigens improved. In human patients transfusion of donor lymphocytes was studied in leukemia recurring after marrow transplantation. It was very effective in the treatment of chronic myelogenous leukemia recurring after marrow transplantation. It was also effective in some patients with acute myeloid leukemia, myelodysplastic syndrome and myeloma; in acute lymphoblastic leukemia and lymphoma responses were rare. Responses in solid tumors as breast cancer have been described. Major complications are graft-versus-host disease and myelosuppression. Myelosuppression could be compensated by the transfusion of marrow. Graft-versus-host disease can be modified by the depletion of CD8-positive T cells from the lymphocyte concentrate or by transfusing very low numbers of cells and increasing doses in a stepwise fashion. The role of concomitant treatment with cytokines and activation of T cells by dendritic cells and vaccination remains to be defined.

Animals↗
PubMed1997

Inflammatory reactions induced by pretransplant conditioning--an alternative target for modulation of acute GvHD and complications following allogeneic bone marrow transplantation?

Intensity of pretransplant conditioning has been closely correlated with regimen related toxicity in patients receiving allogeneic bone marrow transplantation (BMT). In this review, we summarize evidence for a direct link between inflammatory reactions induced by irradiation and cytotoxic treatment and occurrence of acute graft-versus-host disease (GvHD) as well as endothelial complications: In our studies, de novo release of TNFalpha during conditioning was associated with an increased risk of severe GvHD and mortality following BMT, whereas increased spontaneous production of IL-10, an endogenous TNF-antagonist, prior to conditioning protected from these complications. Immunogenetic differences in cytokine regulation and costimulation by endotoxin proved to be important cofactors determining the extent of inflammatory cytokine release in individual patients. Pathophysiological relevance of these findings seems to be confirmed by experimental as well as first clinical trials using TNF-antibodies and related antagonists during pretransplant conditioning. Preclinical experiments suggest additional, cytokine independent inflammatory reactions induced by irradiation such as expression of ICAM-1 and endothelial cell apoptosis. Although the exact impact of these findings on pathophysiology of BMT related complications needs further clarification by future studies, conditioning related inflammation as a first crucial step in induction of GvHD and complications has to be considered when designing new protocols for preparation of patients for allogeneic BMT.

Animals↗
PubMed1996

Protein C, protein S and antithrombin III levels in the course of bone marrow and subsequent liver transplantation due to veno-occlusive disease.

Veno-occlusive disease (VOD) of the liver is one of the most frequent fatal complications after bone marrow transplantation (BMT). A decrease of natural anticoagulants, in particular protein C (PC), has been assumed to be involved in the pathogenesis of the disease. We determined PC and antithrombin III (AT III) levels in two patients undergoing BMT and subsequent liver transplantation due to VOD. Additionally, in one of the patients protein S (PS) levels were also measured. Normal baseline (day-8) PC levels (86 and 89%) were markedly reduced in both patients at the time of VOD manifestation on day 20 and 40, respectively (26 and 31%). PS levels lay within the normal range from day-8 (before myeloablative chemotherapy) until one week after clinical onset of VOD when substitution therapy with fresh frozen plasma (FFP) was initiated. AT III levels decreased moderately during the second and third posttransplant week, but were normal in the patient with a late clinical manifestation of VOD. In both patients PC and PS levels lay within the normal range after liver transplantation which was performed on day 41 and 79, respectively. AT III was substituted several times. Both patients died due to infectious complications on day 141 and 101, respectively. The data confirm previous reports that a decrease of PC is observed in BMT recipients and can be associated with hepatic vein occlusion. Whereas the relevance of AT III is uncertain, PS does not seem to be involved in the pathogenesis of VOD. Liver transplantation lead to normalization of PC levels, but its significance remains to be discussed in terms of ethical justifiability, medical feasibility and costs.

Acute Disease↗
PubMed1996

Influence of bacterial endotoxin on radiation-induced activation of human endothelial cells in vitro and in vivo: protective role of IL-10.

Previous work from our group has contributed to demonstrate the role of conditioning related release of proinflammatory cytokines in induction of acute graft-versus-host disease (GVHD) following allogeneic bone marrow transplantation (BMT). In the present report we show that ionizing radiation (IR) in a clinical relevant dose upregulates intercellular adhesion molecule 1 (ICAM-1) on cultured human microvascular endothelial cells (HMEC). Bacterial endotoxin (lipopolysaccharide, LPS) in a concentration corresponding to serum levels seen during clinical endotoxemia, is capable of further enhancing ICAM-1 expression on irradiated cells. Adhesion assays with freshly isolated peripheral blood mononuclear cells (PBMC) revealed that increased ICAM-1 on IR-treated endothelial cells led to an increased adhesion of PBMC. Again, this effect could be superinduced by LPS. Recombinant human interleukin 10 (IL-10), an antagonistic cytokine known to function as an LPS antagonist, was able to counteract the LPS-mediated enhancement of IR-triggered ICAM-1 induction and PBMC adhesion. In contrast, IL-10 could not inhibit irradiation caused effects. IL-10 seemed to interfere with the translocation of preformed intracellular ICAM-1 to the cell membrane. To investigate whether this superinductive function of IR and LPS on endothelial cells is of clinical relevance, mice were treated with total body irradiation (TBI) and inoculated with a single dose of LPS. Immunohistochemical analyses of murine tissues demonstrated that LPS superinduces IR-triggered ICAM-1 also in vivo. These findings may be of clinical importance as they suggest that the endothelium is activated after radiotherapy or TBI used for conditioning in bone marrow transplantation. The activated endothelium in turn may facilitate the accumulation of effector cells at sites of inflammation.

Animals↗
PubMed1996

Cellular distribution and cellular reactivity of platinum (II) complexes.

We have investigated whether or not the cellular content of reactive platinum, aside from total cellular and DNA-bound platinum, is a measure of the growth inhibitory potential of a given platinum complex. Human MCF-7 breast cancer cells, after treatment with cisplatin [cis-diamminedichloroplatinum(II)] and several 1,2-diphenylethylenediamineplatinum(II) complexes at a fixed dose of 3 microM, were analyzed for their contents of platinum in total cells, isolated nuclei, chromosomal DNA, and the cellular pool of reactive platinum, and compared with ED50-values. Platinum was measured by atomic absorption. Reactive platinum was identified after its reaction with calf thymus DNA that had been added to the cells before their lysis. The amounts of platinum binding to chromosomal DNA were related to previously established ED50-values, and such a correlation could not be found for platinum in total cells, nuclei, and, especially, reactive platinum. The observed differences in the platinum contents of DNA were referred to variations in the rate of adduct formation rather than repair because two representative platinum complexes were indistinguishable by their effects on the chloramphenicol acetyltransferase (EC 2.3.1.28) transfection system. One of the other platinum complexes accumulated, showing an increased growth inhibition in support of this interpretation with regard to the other platinum complexes. During prolonged treatment of MCF-7 cells with the platinum(II) complexes, pools of reactive platinum were found to persist even after drug depletion in the culture medium. This suggested a hitherto unrecognized cellular storage and availability of reactive platinum.

Antineoplastic Agents↗
PubMed1996

Late pulmonary impairment following allogeneic bone marrow transplantation.

The pulmonary function of 88 consecutive leukemic patients who had undergone allogeneic bone marrow transplantation (BMT) was studied beforehand, at 3 months, at 6 months, and annually thereafter until 5 years after grafting. The parameters for function which are indicative for obstructive and restrictive lung disease deteriorated in all patient groups during the first 3 to 6 months after BMT but partially recovered within one year. Long-term decline in lung function was similar in all patient groups, and neither the onset nor the magnitude of pulmonary dysfunction was related to the occurrence of pulmonary impairment within 6 months after grafting. Multivariate analysis was then employed to assess predictors for long-term pulmonary disease. Despite the obvious effect of chronic graft versus host disease on the course of lung function, it was in itself not a significant predictor of long-term pulmonary outcome. Rather, the conditioning regimen turned out to be indicative; compared with busulfan, fractionated total body irradiation was demonstrated to be clearly superior with a lower incidence of both restrictive and obstructive long-term lung impairment. Our data indicate a previously unknown long-term side effect of busulfan conditioning.

Adult↗
PubMed1996

Multiple sclerosis: prospective analysis of TNF-alpha and 55 kDa TNF receptor in CSF and serum in correlation with clinical and MRI activity.

The possibility of antagonizing tumor necrosis factor-alpha (TNF-alpha) in vivo with antibodies or soluble TNF receptor has focused much interest on the role of this cytokine in the natural course of MS. We studied nine patients prospectively and serially for one year (14 time points, 131 observations). TNF-alpha and the 55 kDa soluble TNF receptor were measured every 4 weeks in the serum and at defined time points in the CSF. Each value was correlated to clinical symptoms and to MRI measurements obtained on the same day. All patients with relapsing-remitting disease showed periodic increases of TNF concentrations. Overall, the association between serum TNF-alpha levels and bursts of Gd-DTPA enhancement on cranial MRI was not sufficiently tight to reach statistical significance. However, serum TNF levels > 50 pg/ml and measurable CSF levels were always associated with Gd-DTPA enhancing MRI lesions. Isolated high serum TNF peaks were noted during episodes of infection, hay fever or psychic stress. After treatment with glucocorticoids, TNF levels were suppressed for several months, whereas new Gd-DTPA enhancing lesions continued to appear. The concentrations of the soluble 55 kDa TNF receptor did not show marked fluctuations. These results are consistent with an active role of TNF-alpha in MS during periods of disease activity and provide further support for the clinical evaluation of anti-TNF therapies.

Adult↗
PubMed1996

Effect of growth factors on estrogen receptor mediated gene expression.

The proliferation of mammary carcinoma cells can be stimulated by estrogens and various growth factors such as EGF and IGF-I. Steroid hormones and growth factors are understood to exert their effects via different receptors and signal transduction pathways. Recently, it has been shown that growth factors can utilize the unliganded estrogen receptor (ER) as a transcription factor. This study was aimed at identifying the growth factors that can act via the estrogen receptor, and finding new estrogen antagonists that block this activity. Originally, a transcription assay was used in which HeLa cells had been transiently co-transfected with the expression vector for the human ER and a reporter plasmid EREwtc luc. EGF and, to a lesser extent, insulin stimulated the expression of the reporter gene in the absence of estradiol (E2), whereas IGF-I was inactive. The stimulatory effect of E2 and insulin was suppressed when the ER was blocked by the pure antiestrogen ICI 182,780. In ER-positive MCF-7 cells, transfected transiently with the reporter plasmid, EGF had no stimulatory effect on luciferase expression. IGF-I stimulated the transcription to about 50% of the E2 value. Similar activity was found for insulin. The effect of both growth factors was only partly reversed by the addition of a pure antiestrogen. The combination of E2 and IGF-I or insulin led to a synergistic activation of transcription. Because transiently transfected cells do not allow one to study the influence of chromatin structure on gene expression, an MCF-7 subline (MCF-7/2a) was established, in which the reporter construct had been integrated in the genome. IGF-I stimulated luciferase expression in these cells, but showed no overadditive effect with E2. The effects of both agents were completely suppressed by the pure antiestrogen ICI 182,780. These data suggest the existence of an ER-independent mechanism for the activation of the reporter gene in transiently transfected cells, but not in stable transfectants.

Breast Neoplasms↗
PubMed1996

Protein kinase C activation is involved in ultraviolet B irradiation-induced endothelial cell ICAM-1 up-regulation and lymphocyte-endothelium interaction in vitro.

Lymphocyte-endothelium interactions are pivotal steps in mediating inflammatory responses. The authors have analysed the influence of ultraviolet B (UVB) irradiation on intercellular adhesion molecule (ICAM)-1 expression on cells of the human microvascular endothelial cell line (HMEC)-1 and the intracellular signalling pathways involved. Flow cytometry revealed dose-dependent ICAM-1 up-regulation with maximum induced expression 24h after sublethal UVB irradiation of 10 mJ/cm2. While anti-tumour necrosis factor (TNF)-alpha antibodies or recombinant human interleukin (IL)-10 did not influence this response, anti-interferon (IFN)-gamma antibodies blocked the UVB-induced ICAM-1 up-regulation. Significant induction of intracellular/membrane-bound IFN-gamma was measured as early as 6 h post-UVB. Since previous work has shown a differential role of protein kinase C (PKC) in cytokine induced ICAM-1 expression, the effect of a selective bisindolylmaleimide-derived PKC-inhibitor (GF109203X) was studied. Ultraviolet B-induced ICAM-1 up-regulation was effectively blocked by the PKC-inhibitor, whereas a PKA-inhibitor was ineffective. Moreover, immunofluorescence analysis showed a radiation-induced membrane translocation of PKC-alpha, indicative of enzyme activation, in HMEC-1 cells already 30 min post-UVB. The functional relevance of the UVB-induced ICAM-1 expression and involvement of PKC in this process was demonstrated in an adhesion assay with peripheral blood mononuclear cells. In conclusion, UVB-induced ICAM-1 expression on human endothelial cells involves PKC-dependent pathways and can be prevented by a PKC-inhibitor. The use of PKC-inhibitors as additive modulators in immune reactions may bear clinical potential. The mechanisms of IFN-gamma induction in endothelial cells by UVB deserve further investigation.

Cell Adhesion↗
PubMed1996

Hemostatic parameters in sepsis patients treated with anti-TNF alpha-monoclonal antibodies.

Tumor necrosis factor-alpha (TNF alpha) is a central mediator in the pathogenesis of sepsis. It also interferes with the hemostatic system and exerts and a net procoagulant effect. Since TNF alpha may contribute to thrombotic complications in sepsis patients, we determined markers of thrombin activation, parameters of the fibrinolytic system (D-dimer, tissue plasminogen activator antigen (tPA) urinary type plasminogen activator antigen (uPA), plasminogen activator inhibitor antigen (PAI-1) and von Willebrand factor antigen (vWF) in 30 patients with sepsis or septic shock. All patients were treated with standard therapy, but 14 patients were treated additionally with an anti-TNF alpha monoclonal antibody (MAK 195F); 16 patients served as historical controls. No significant effect of the antibody on the parameters of the hemostatic system could be determined. Our data speak against a modulation of coagulation or the fibrinolytic system by the monoclonal anti-TNF alpha antibody MAK 195F in this cohort of sepsis patients.

Adult↗
PubMed1996

Graft-versus-host reaction spares normal stem cells in chronic myelogenous leukemia.

Chronic myelogenous leukemia is a clonal proliferative disorder of pluripotent hematopoietic stem cells. Cure may be achieved by myeloablative conditioning treatment and marrow transplantation. In addition, allogeneic marrow can exert a graft-versus-leukemia effect. The graft-versus-leukemia effect may be directed against leukemia-specific antigens or against antigens on all hematopoietic cells, or it can be part of a graft-versus-host reaction. We report an informative post-transplant course of a patient with yet another leukemia-specific effect. This patient was transplanted with marrow from his HLA-identical sister in an advanced phase of CML and developed acute and chronic GVHD. After a severe pneumonia a high proportion of his metaphases in the bone marrow were male and Philadelphia chromosome negative. Later all metaphases were again female and leukemic cells could not be detected by reverse transcriptase polymerase chain reaction analysis (RT-PCR) for BCR/ABL. This course indicates that normal hematopoietic stem cells may survive intensive chemotherapy, bone marrow transplantation and GVHD. They may be recruited from a dormant state into proliferation during severe infections. In contrast, CML may be eliminated by the graft-versus-host reaction that recognizes recruited cells and spares dormant cells.

Adult↗
PubMed1996

Nuclear accumulation and homeostasis of the unusual polymer beta-poly (L-malate) in plasmodia of Physarum polycephalum.

The plasmodium of Physarum polycephalum specifically contains an unusual polyester, beta-poly(L-malate), which is not found in any of the mononucleate forms of its life cycle. Plasmodia growing on D-glucose have been analyzed for beta-poly(L-malate) in nuclei, cytosol and culture medium after cell fractionation, purification by chromatography on DEAE-cellulose and digestion of proteins/nucleic acids. Nuclei contained 400 micrograms polymer per 1 g of plasmodia, corresponding to a nuclear concentration of 230 mM L-malyl residues, not depending on growth rates, lengths of growth periods, and the growth form as micro- or macroplasmodia. The synthetic rate increased during the phase of rapid enlargement of the nuclei after mitosis. Beta-Poly(L-malate) was polydisperse in molecular mass, these tending to be higher in nuclear than in cytosolic extracts and being lowest in the culture medium. Beta-Poly(L-malate) was not degraded when contained in plasmodia, in contrast to degradation and the occurrence of low molecular mass polymer in the culture medium. During pulse-chase feeding with D-[14C]glucose (0.8 micrometerCi/mol), beta-[14C]poly(L-malate) appearance followed kinetics indicating a release of polymer from nuclei into the culture medium when it was in excess of a threshold. Injection experiments with purified beta-[14C]poly(L-malate) revealed a re-entry from the cytoplasm into the nuclei and thus the possibility of commutation between the cytoplasm and the nuclei. The observed homeostasis in nuclei supports the assumption that beta-poly(L-malate) plays an essential role in growing plasmodia.

Animals↗