Mycolactone diffuses from Mycobacterium ulcerans-infected tissues and targets mononuclear cells in peripheral blood and lymphoid organs

Background

Buruli ulcer (BU) is a progressive disease of subcutaneous tissues caused by Mycobacterium ulcerans. The pathology of BU lesions is associated with the local production of a diffusible substance, mycolactone, with cytocidal and immunosuppressive properties. The defective inflammatory responses in BU lesions reflect these biological properties of the toxin. However, whether mycolactone diffuses from infected tissues and suppresses IFN-γ responses in BU patients remains unclear.

Methodology/Principal Findings

Here we have investigated the pharmacodistribution of mycolactone following injection in animal models by tracing a radiolabeled form of the toxin, and by directly quantifying mycolactone in lipid extracts from internal organs and cell subpopulations. We show that subcutaneously delivered mycolactone diffused into mouse peripheral blood and accumulated in internal organs with a particular tropism for the spleen. When mice were infected subcutaneously with M. ulcerans, this led to a comparable pattern of distribution of mycolactone. No evidence that mycolactone circulated in blood serum during infection could be demonstrated. However, structurally intact toxin was identified in the mononuclear cells of blood, lymph nodes and spleen several weeks before ulcerative lesions appear. Importantly, diffusion of mycolactone into the blood of M. ulcerans–infected mice coincided with alterations in the functions of circulating lymphocytes.

Conclusion

In addition to providing the first evidence that mycolactone diffuses beyond the site of M. ulcerans infection, our results support the hypothesis that the toxin exerts immunosuppressive effects at the systemic level. Furthermore, they suggest that assays based on mycolactone detection in circulating blood cells may be considered for diagnostic tests of early disease.     

Localization of PNA-binding and nonbinding thymus cells in peripheral lymphoid organs

Thymus cells were labeled in vitro with FITC and injected into syngeneic recipients. In cell suspensions of lymphoid organs green cells were inspected for PNA receptors with double immunofluorescence. A striking preference of PNA-negative cells to localize in lymph nodes and the lymphoid compartment of the spleen was demonstrated. Incubation with anti-Ly sera revealed that Ly 1⁺ PNA-negative cells homed in popliteal lymph nodes and Peyer's patch but not in mesenteric lymph nodes.     

Kurloff cell proteoglycans. Evidence for de novo synthesis of chondroitin sulphate proteoglycans by purified Kurloff cells

This paper reports the first direct demonstration of de novo synthesis of chondroitin sulphate proteoglycans by Kurloff cells. This was achieved using highly purified splenic Kurloff cells labelled in vitro with [35S]sulphate and D-[U-3H]glucosamine. A single population of sulphated proteoglycans was observed after dissociative extraction, DEAE-cellulose chromatography, Sepharose CL 6B chromatography and fluorography after electrophoresis. These were large, highly anionic proteoglycans and were completely digested by chondroitinase AC or ABC. Moreover, glycosaminoglycan extracted from Kurloff cells had the electrophoretic mobility of control chondroitin sulphate.     

Cytochemical localization of acid phosphatase and trimetaphosphatase activities in Kurloff cells

After stimulation of guinea pigs with estradiol to increase their Kurloff cell number, spleen imprints were prepared in order to detect non-specific acid phosphatase (AcPase) activity by light microscopic cytochemistry using naphthol AS-BI phosphate as substrate and pararosanilin or fast garnet GBC as coupler. For ultracytochemistry, Kurloff cells were prepared from spleens by filtration through a homogeneizer screen followed by repeated centrifugation. AcPase and trimetaphosphatase activities were tested using beta-glycerophosphate, cytidine-5'-monophosphate and inorganic trimetaphosphate as substrates. Significant enzymatic activities were demonstrated with all the substrates used in the cytoplasmic inclusion body of the Kurloff cells.     

Fibrinogen or its derivatives in the Kurloff cells.

We have investigated the occurrence of fibrinogen or its derivatives in the Kurloff bodies of female guinea pigs by means of immunofluorescence, histochemistry and ultrastructural analysis. The Kurloff bodies are fluorescent after incubation with anti-guinea pig fibrinogen immuno-globulins coupled with fluorescein isothiocyanate. PTAH, Martius scarlet blue, Masson 44--41, Picro-Mallory V stain the Kurloff bodies just as they stain fibrin and fibrinoid. However, the ultrastructure of the central mass of the Kurloff body is finely granular without fibrils. Thus the Kurloff body contains no fibrin but incompletely polymerized fibrinogen derivatives or breakdown products of fibrin.     

Characterization of glucocerebrosidase in peripheral blood cells and cultured blastoid cells

We have characterized glucocerebrosidase in various cell types of peripheral blood of control subjects and in cultured human blastoid cells. The intracellular level of glucocerebrosidase in cultured blastoid cells (10-30 nmol substrate hydrolyzed/h.mg protein) resembles closely values observed for leukocyte cell types and various tissues and is significantly lower than that observed in cultured fibroblasts (150-500 nmol substrate hydrolyzed/h.mg protein). Glucocerebrosidase is extracted from leukocyte cell types and cultured blastoid cells almost exclusively in a monomeric, nonactivated form with enzymatic properties identical to those of the tissue enzyme. In contrast, extracts of platelets are rich in an aggregated, activated form of the enzyme. Glucocerebrosidase in blood cells and cultured blastoid cells is heterogeneous with respect to Mr and pI due to a heterogeneous oligosaccharide composition of the enzyme. The different forms seen represent intermediates in the biosynthesis and maturation of the enzyme. Blastoid cells should thus be an attractive model system for studying the natural history of glucocerebrosidase in a cell type related to those cells involved in the pathology of Gaucher disease.     

Phosphofructokinase isozymes from human organs and blood cells.

Phosphofructokinase (PFK) isozymes of blood cells and some human tissues were studied by starch gel electrophoresis and immunoprecipitation by anti-muscle and anti-erythrocyte PFK sera. PFK from muscle, heart, brain and placenta were totally precipitated by both antisera. PFK from blood cells (erythrocytes, lymphocytes, granulocytes, platelets) were precipitated more strongly by anti-erythrocyte PFK serum than by anti-muscle PFK serum. Liver, kidney and monoblast PFK were slightly precipitated by both antisera. From the electrophoretic patterns and the immunoprecipitation curves we may conclude that muscle contains the homotetrameric M4 forms; platelet, liver and kidney the homotetrameric E4 form, and blood cells the M-E hybrids. Monoblasts probably contain a E4 type PFK precursor, and heart, placenta and brain, a modified M4 type PFK. Other isozymes, unrelated with muscle and erythrocyte, were revealed in liver and kidney.     

Lymphatic vessels and Kurloff cells in the thymus of estradiol-treated guinea pigs

Summary Male guinea pigs were given a single subcutaneous injection of estradiol, which induces formation of Kurloff cells, and serial sections of thymus were examined after 10, 12, 15 and 21 days. Kurloff cells were found in large numbers in lymphatic vessels, both outside the thymus, in the interlobular tissue, at the cortical surface and inside the cortex, suggesting migration via such structures. Large extrathymic or interlobular lymphatics communicated with a previously undescribed thymic structure-the lymphatic centre-surrounded by a marginal sinus. The orientation of lymphatic valves, and the concentration of Kurloff cells within this lymphatic centre at an early time after the administration of estradiol, indicate the existence of an afferent migratory pathway. The different morphology at different times after estradiol suggest that the treatment caused a dynamic remodeling of thymic lymphatic structures.     

Purification of natural killer-like Kurloff cells and arachidonic acid metabolism.

Pulmonary and splenic Kurloff cells have been purified from estrogen-treated guinea pig. Enzymatic digestion of lung tissue and mechanical dispersion of cells yielded about 650 x 10(6) viable cells. After centrifugal elutriation and centrifugation on continuous Percoll gradient, a population of high-density (1,100 g/ml) pulmonary Kurloff cells were obtained with high viability (approximately 99%) and purity (approximately 99%). Splenic Kurloff cells have been isolated by disruption of spleen tissue and centrifugation on continuous Percoll gradient. High-density splenic Kurloff cells (150 x 10(6) cells per spleen) were also obtained with high purity (approximately 99%) and viability (approximately 99%). Pulmonary and splenic Kurloff cells were incubated with various concentrations of arachidonic acid (10, 30 and 100 microM) in the absence or presence of 2 microM ionophore A23187. With 10 microM arachidonic acid the relative production of cyclooxygenase products was the following: TxB2 greater than PGE2 approximately PGI2. For an arachidonic acid concentration superior to 10 microM, the profile of release was PGE2 much greater than TxB2 greater than PGI2. Arachidonic acid metabolism through the 5-lipoxygenase pathway was also studied by incubating pulmonary or splenic Kurloff cells with 10 microM arachidonic acid in the absence or presence of 2 microM ionophore A23187, or in some experiments, with 2.5 microM leukotriene A4. Reverse phase HPLC profiles clearly indicated that high-density Kurloff cells did not express 5-lipoxygenase activity. However, these cells showed the ability to convert exogenous leukotriene A4 into leukotriene B4 suggesting the presence of LTA4 hydrolase activity. These data have been confirmed by a sensitive RIA method. This study constitutes the first report on the purification of pulmonary Kurloff cells and on arachidonic acid metabolism by these cells. The possible implications of Kurloff cells in various biological events are discussed.     

Presence of low affinity estrogen binding sites in guinea-pig Kurloff cells

Estrogen treatment of guinea-pig leads to an increase in the number of lymphoid cells containing Kurloff inclusions. The presence of estradiol binding sites in cytosolic extracts of Kurloff cells was investigated. We confirm here our previous inability to measure the typical type I estrogen receptor by using the classical dextran-charcoal procedure to separate bound and free ligand. We report now that low affinity estrogen binding sites (Kd approximately equal to 11 nM) can be detected when Kurloff cell extracts were fractionated on hydroxylapatite or Sephadex LH-20 after binding assay. Although the real function of these binding sites remains to be defined, the question arises again whether Kurloff cell represents a target cell for estrogens.     

Mobilization and harvesting of peripheral blood stem cells

The use of peripheral blood stem cells (PBSC) as a source of hematopoietic stem cells is steadily increasing and has nearly supplanted bone marrow. The present article reviews mobilization and collection of PBSC as well as its side effects. Specialized harvesting strategies such as large volume leukapheresis (LVL) and pediatric PBSC collection are included in this overview. Under steady state conditions, less than 0.05% of the white blood cells (WBC) are CD34+ cells. Chemotherapy results in a 5-15-fold increase of PBSC. Combining chemotherapy and growth factors increases CD34+ cells up to 6% of WBC. In the allogeneic setting, granulocyte-colony stimulating factor is used alone for PBSC mobilization. Several factors affect the mobilization of PBSC: age, gender, type of growth factor, dose of the growth factor and in the autologous setting, patient's diagnosis, chemotherapy regimen and number of previous chemotherapy cycles or radiation. Harvesting of PBSC can be performed with various blood cell separators using continuous or discontinuous flow technique. Continuous flow separators allow the processing of more blood compared with intermittent flow devices resulting in higher yields of CD34+ cells for transplantation. LVL can be used to increase the CD34+ yield in patients with low CD34+ pre-counts. Processing of more blood in LVL is achieved by an increase of the blood flow rate and an altered anticoagulation regimen. Specialized strategies were developed for pediatric PBSC collection considering the main limiting factors, extracorporeal volume and vascular access. Adverse events in PBSC collection can be subdivided in apheresis associated and mobilization associated side effects. Citrate reactions due to hypocalcemia are frequent during apheresis, especially in pediatric PBSC collection and LVL. Thrombocytopenia is often observed in patients after termination of apheresis due to platelet loss during PBSC harvesting. Muscle and bone pain are frequent adverse events in allogeneic stem cell mobilization but are usually tolerated under the use of analgesics. Spleen enlargement followed by rupture is a serious complication in allogeneic donors.     

Colony-forming and colony-stimulating cells in normal human peripheral blood

Peripheral white blood cells (WBC) from normal persons form colonies of granulocytic cells in vitro in soft agar. Stimulus was provided by a feeder layer of peripheral WBC. By centrifugation through an Isopaque-Ficoll gradient, the cells were separated into a mononuclear and a granulocytic fraction with a purity of 96–98% in each fraction. Both the colony-forming cells and the cells inducing colony formation were found in the mononuclear cell fraction. Further fractionation of these mononuclear cells on adherence glass bead columns showed that the colony-forming and colony-inducing cells do not belong to the small lymphocyte population, but were found in the glass adherent fraction containing large monocyte-like and atypical mononuclear cells.     

Brain and gut neuropeptides in peripheral blood mononuclear cells

Neuropeptides, initially thought to be common features of gut and brain, are only synthesized in immune cells and modulate immune functions. The presence and possible functions of these peptides in immune cells in both physiological or pathological conditions have been investigated in our laboratory in the last years. Some of the data obtained are reviewed here, and future developments of the field are indicated.     

Cryopreserving human peripheral blood progenitor cells

High-dose chemotherapy followed by autologous peripheral blood progenitor cell (PBPC) transplantation is used in the treatment of chemosensitive malignancies. Cryopreservation of PBPC in 10% dimethyl sulfoxide (DMSO) has been the standard procedure in most institutions. Infusion of PBPC cryopreserved with DMSO can be associated with toxic reactions such as vomiting, cardiac dysfunction, anaphylaxia and acute renal failure. The grade of toxicity experienced by patients is related to the amount of DMSO present in the PBPC. Cryopreservation with lower DMSO concentrations would be expected to reduce the toxicity. In recent studies done with PBPC cells cryopreserved with 5%, 4% and 2% DMSO, using 10% DMSO as a reference control, CD34+ cells were investigated for preservation of viability, apoptosis, and necrosis. Also preservation of mature colony-forming (CFU) cells, specifically mature myeloid, erythroid progenitors, CFU-megakaryocytes and long-term culture-initiating cells (LTC-ICs) were investigated, using 5% and 10% DMSO as cryoprotectant. All samples were frozen in a rate-controlled programmed freezer and stored in the vapor phase of liquid nitrogen until used. Conclusion: 5% DMSO is the optimal concentration for cryopreserving human PBPC in vitro. Consequently, some hospitals have started using 5% DMSO as cryoprotectant for the autologous PBPC as a standard procedure.     

Proteomic map of peripheral blood mononuclear cells

In the field of proteomics extensive efforts have been focused on the knowledge of proteins expressed by different cell types. In particular, enormous progress has been done in the characterization of blood cellular components. In this work, we have established a public 2-DE database for human peripheral blood mononuclear cells (PBMCs) proteins. Two hundred and forty-six spots corresponding to 174 different proteins have been identified on 2-DE gels from PBMCs isolated from six healthy individuals. All the identified proteins have been classified in thirteen categories on the basis of their differential functions or cellular localization and annotated at the http://physiology.unile.it/proteomics. The role of several proteins has been discussed in relation to their biological function. We intend to show the potentiality of PBMCs to investigate the proteomics changes possibly associated with a large number of pathologies such as autoimmune, neurodegenerative and cancer diseases.