Transplantation of Dystrophin Expressing Chimeric Human Cells of Myoblast/Mesenchymal Stem Cell Origin Improves Function in Duchenne Muscular Dystrophy Model.

Duchenne muscular dystrophy (DMD) is a lethal X-linked disorder caused by mutations in dystrophin gene. Currently, there is no cure for DMD. Cell therapies are challenged by limited engraftment and rejection. Thus, more effective and safer therapeutic approaches are needed for DMD. We previously reported increased dystrophin expression correlating with improved function after transplantation of dystrophin expressing chimeric (DEC) cells of myoblast origin in the mdx mouse models of DMD. This study established new DEC cell line of myoblasts and mesenchymal stem cells (MSC) origin and tested its efficacy and therapeutic potential in mdx/scid mouse model of DMD. Fifteen ex vivo cell fusions of allogenic human myoblast [normal myoblasts (MBN)] and normal human bone marrow-derived MSC (MSCN) from normal donors were performed using polyethylene glycol. Flow cytometry, confocal microscopy, polymerase chain reaction (PCR)-short tandem repeats, polymerase chain reaction-reverse sequence-specific oligonucleotide probe assessed chimeric state of fused MBN/MSCN DEC cells, whereas Comet assay assessed fusion procedure safety testing genotoxicity. Immunofluorescence and real-time PCR assessed dystrophin expression and myogenic differentiation. Mixed lymphocyte reaction (MLR) evaluated DEC's immunogenicity. To test MBN/MSCN DEC efficacy in vivo, gastrocnemius muscle of mdx/scid mice were injected with vehicle (n = 12), nonfused MBN and MSCN (n = 9, 0.25 × 106/each) or MBN/MSCN DEC (n = 9, 0.5 × 106). Animals were evaluated for 90 days using ex vivo and in vivo muscle strength tests. Histology and immunofluorescence staining assessed dystrophin expression, centrally nucleated fibers and scar tissue formation. Post-fusion, MBN/MSCN DEC chimeric state, myogenic differentiation, and dystrophin expression were confirmed. MLR reveled reduced DEC's immune response compared with controls (P < 0.05). At 90 days post-DEC transplant, increase in dystrophin expression (20.26% ± 2.5%, P < 0.05) correlated with improved muscle strength and function in mdx/scid mice. The created human MBN/MSCN DEC cell line introduces novel therapeutic approach combining myogenic and immunomodulatory properties of MB and MSC, and as such may open a universal approach for muscle regeneration in DMD.

Parthenogenesis as a Solution to Hybrid Sterility: The Mechanistic Basis of Meiotic Distortions in Clonal and Sterile Hybrids.

Hybrid sterility is a hallmark of speciation, but the underlying molecular mechanisms remain poorly understood. Here, we report that speciation may regularly proceed through a stage at which gene flow is completely interrupted, but hybrid sterility occurs only in male hybrids whereas female hybrids reproduce asexually. We analyzed gametogenic pathways in hybrids between the fish species Cobitis elongatoides and C. taenia, and revealed that male hybrids were sterile owing to extensive asynapsis and crossover reduction among heterospecific chromosomal pairs in their gametes, which was subsequently followed by apoptosis. We found that polyploidization allowed pairing between homologous chromosomes and therefore partially rescued the bivalent formation and crossover rates in triploid hybrid males. However, it was not sufficient to overcome sterility. In contrast, both diploid and triploid hybrid females exhibited premeiotic genome endoreplication, thereby ensuring proper bivalent formation between identical chromosomal copies. This endoreplication ultimately restored female fertility but it simultaneously resulted in the obligate production of clonal gametes, preventing any interspecific gene flow. In conclusion, we demonstrate that the emergence of asexuality can remedy hybrid sterility in a sex-specific manner and contributes to the speciation process.

Development of immortalized human hepatocyte-like hybrid cells by fusion of multi-lineage progenitor cells with primary hepatocytes.

Human primary hepatocytes (PHs) are critical to studying liver functions, drug metabolism and toxicity. PHs isolated from livers that are unacceptable for transplantation have limited expansion and culture viability in vitro, in addition to rapidly deteriorating enzymatic functions. The unsuitability of immortalized hepato-carcinoma cell lines for this function has prompted studies to develop hepatocyte-like cells from alternative sources like ESC, iPS, and other stem cell types using differentiation protocols. This study describes a novel technique to produce expandable and functional hepatocyte-like cells from the fusion of an immortalized human umbilical cord blood derived cell line (E12 MLPC) to normal human primary hepatocytes. Multi-lineage progenitor cells (MLPC) comprise a small subset of mesenchymal-like cells isolated from human umbilical cord blood. MLPC are distinguishable from other mesenchymal-like cells by their extended expansion capacity (up to 80 cell doublings before senescence) and the ability to be differentiated into cells representative of endo-, meso- and ectodermal origins. Transfection of MLPC with the gene for telomerase reverse transcriptase (TERT) resulted in clonal cell lines that were capable of differentiation to different cellular outcomes while maintaining their functional immortality. A methodology for the development of immortalized hepatocyte-like hybrid cells by the in vitro fusion of human MLPC with normal human primary hepatocytes is reported. The resultant hybrid cells exhibited homology with hepatocytes by morphology, immunohistochemistry, urea and albumin production and gene expression. A medium that allows stable long-term expansion of hepatocyte-like fusion cells is described.

Electro Cell Fusion for Hybridoma Production.

Once a good immune response has developed in an animal and an appropriate screening procedure has been developed, the construction of hybridomas is ready to begin. The electro cell fusion (electrofusion) method uses an electrical field in the form of short, intense pulses to increase the permeability of the membrane. The resulting local perforation of the cell membrane induces the cells to fuse, forming hybridomas. Electrofusion is accomplished in three steps: Prealignment of the cells (convergence and cell contact), membrane fusion, and postalignment (rounding off the fused cells). This method has been applied successfully to hybridoma production with higher efficiency than routine polyethylene glycol fusion, allowing production of more hybrid cells.

Fusion-mediated chromosomal instability promotes aneuploidy patterns that resemble human tumors.

Oncogenesis is considered to result from chromosomal instability, in addition to oncogene and tumor-suppressor alterations. Intermediate to aneuploidy and chromosomal instability, genome doubling is a frequent event in tumor development but the mechanisms driving tetraploidization and its impact remain unexplored. Cell fusion, one of the pathways to tetraploidy, is a physiological process involved in mesenchymal cell differentiation. Besides simple genome doubling, cell fusion results in the merging of two different genomes that can be destabilized upon proliferation. By testing whether cell fusion is involved in mesenchymal oncogenesis, we provide evidence that it induces genomic instability and mediates tumor initiation. After a latency period, the tumor emerges with the cells most suited for its development. Furthermore, hybrid tumor genomes were stabilized after this selection process and were very close to those of human pleomorphic mesenchymal tumors. Thus genome restructuring triggered by cell fusion may account for the chromosomal instability involved in oncogenesis.

In vitro differentiation of mouse T cell-derived hybrid cells obtained through cell fusion with embryonic stem cells.

Nuclear reprogramming is an innovative advance in cell biology. An important research initiative in this field is cell fusion-mediated nuclear reprogramming, wherein the nuclei of somatic cells, such as thymocytes, are initialized through cell fusion with embryonic stem cells (ESCs). However, hybrid cells obtained through cell fusion between ESCs and thymocytes failed to contribute to the embryo proper when injected into blastocysts, which suggested that there are fundamental defects in such hybrid cells. Here, we performed side-by-side comparative analyses of the in vitro growth and differentiation capacities of ESCs and ESC-T hybrid cells. We found that the hybrid cells were larger and proliferated more slowly than the ESCs in 2i/LIF medium. Upon in vitro induction of differentiation, hybrid cells gave rise to cells of the three germ layers. Under culture conditions for hematopoietic differentiation, hybrid cells successively differentiated into lateral mesodermal cells, hemogenic endothelial cells, and various types of hematopoietic cells, including erythroid, myeloid, and lymphoid cells, although T cell maturation in the CD4/CD8 double-negative fraction was delayed. These results verified the multi-lineage differentiation capacity of ESC-T hybrid cells. The minimal contribution of hybrid cells to chimeric embryos may be due to their slow growth.

Conserved pathway activation following xenogeneic, heterotypic fusion.

Fusion between cells of different organisms (i.e., xenogeneic hybrids) can occur, and for humans this may occur in the course of tissue transplantation, animal handling, and food production. Previous work shows that conferred advantages are rare in xenogeneic hybrids, whereas risks of cellular dysregulation are high. Here, we explore the transcriptome of individual xenogeneic hybrids of human mesenchymal stem cells and murine cardiomyocytes soon after fusion and ask whether the process is stochastic or involves conserved pathway activation. Toward this end, single-cell RNA sequencing was used to analyze the transcriptomes of hybrid cells with respect to the human and mouse genomes. Consistent with previous work, hybrids possessed a unique transcriptome distinct from either fusion partner but were dominated by the cardiomyocyte transcriptome. New in this work is the documentation that a few genes that were latent in both fusion partners were consistently expressed in hybrids. Specifically, human growth hormone 1, murine ribosomal protein S27, and murine ATP synthase H+ transporting, mitochondrial Fo complex subunit C2 were expressed in nearly all hybrids. The consistent activation of latent genes between hybrids suggests conserved signaling mechanisms that either cause or are the consequence of fusion of these 2 cell types and might serve as a target for limiting unwanted xenogeneic fusion in the future.-Yuan, C., Freeman, B. T., McArdle, T. J., Jung, J. P., Ogle, B. M. Conserved pathway activation following xenogeneic, heterotypic fusion.

Monochromosomal Hybrids and Chromosome Transfer: A Functional Approach for Gene Identification.

Functional complementation of cellular defects has been a valuable approach for localizing causative genes to specific chromosomes. The complementation strategy was followed by positional cloning and characterization of genes for their biological relevance. We herein describe strategies used for the construction of monochromosomal hybrids and their applications for cloning and characterization of genes related to cell growth, cell senescence and DNA repair. We have cloned RNaseT2, GluR6 (glutamate ionotropic receptor kainate type subunit 2-GRIK2) and protein tyrosine phosphatase, receptor type K (PTPRK) genes using these strategies.

A phosphorylation-wide sncRNA screen reveals Protein Functional Effector sncRNAs (pfeRNAs) in human lung somatic cells.

We recently reported that PIWI-interacting RNAs likes (piR-Ls) could regulate functions of the interacting phosphorylated proteins (p-Proteins). In addition, except for writers and erasers, functional efficacy of p-Proteins on their readers still remains unknown. We, therefore, reasoned there was a type of sncRNAs which could regulate functional efficacy of p-Proteins. Here, we profiled sncRNAs interacting with phosphorylated -Ser, -Thr and -Tyr residues in 3 HBE and 4 lung SCC cell lines, investigated effects and mechanisms of phosphorylated-residue-interacting sncRNAs. Our results demonstrated sncRNAs regulating functional efficacy of p-Proteins and we thus referred them as Protein Functional Effector sncRNAs (pfeRNAs). pfeRNAs were distributed among 26 to 50 nucleotides, shared some core sequences and showed distinctive expression patterns between HBE and SCC cells. Core sequences 417 (CS417), showing consistent upregulation in all 4 SCC cells, bound directly to p-Nucleolin (NCL), which was dependent on the key elements CGCG of CS417 and p-Ser619 of NCL. The CS417/p-NCL interaction was critical for functional efficacy of p-NCL in basic activities of lung normal and cancer cells. Thus, we revealed a novel type of pfeRNAs controlling functional efficacy of p-Proteins in lung somatic cells.

The influence of reference radiation photon energy on high-LET RBE: comparison of human peripheral lymphocytes and human-hamster hybrid AL cells.

The relative biological effectiveness (RBE) based on the induction of dicentrics in any cell type is principally an important information for the increasing application of high-LET radiation in cancer therapy. Since the standard system of human lymphocytes for measuring dicentrics are not compatible with our microbeam irradiation setup where attaching cells are essential, we used human-hamster hybrid AL cells which do attach on foils and fulfil the special experimental requirement for microbeam irradiations. In this work, the dose-response of AL cells to photons of different energy, 70 and 200 kV X-rays and 60Co γ-rays, is characterized and compared to human lymphocytes. The total number of induced dicentrics in AL cells is approximately one order of magnitude smaller. Despite the smaller α and ß parameters of the measured linear-quadratic dose-response relationship, the α/ß-ratio versus photon energy dependence is identical within the accuracy of measurement for AL cells and human lymphocytes. Thus, the influence of the reference radiation used for RBE determination is the same. For therapy relevant doses of 2 Gy (60Co equivalent), the difference in RBE is around 20% only. These findings indicate that the biological effectiveness in AL cells can give important information for human cells, especially for studies where attaching cells are essential.

Mesenchymal stem cells generate distinct functional hybrids in vitro via cell fusion or entosis.

Homotypic and heterotypic cell-to-cell fusion are key processes during development and tissue regeneration. Nevertheless, aberrant cell fusion can contribute to tumour initiation and metastasis. Additionally, a form of cell-in-cell structure called entosis has been observed in several human tumours. Here we investigate cell-to-cell interaction between mouse mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs). MSCs represent an important source of adult stem cells since they have great potential for regenerative medicine, even though they are also involved in cancer progression. We report that MSCs can either fuse forming heterokaryons, or be invaded by ESCs through entosis. While entosis-derived hybrids never share their genomes and induce degradation of the target cell, fusion-derived hybrids can convert into synkaryons. Importantly we show that hetero-to-synkaryon transition occurs through cell division and not by nuclear membrane fusion. Additionally, we also observe that the ROCK-actin/myosin pathway is required for both fusion and entosis in ESCs but only for entosis in MSCs. Overall, we show that MSCs can undergo fusion or entosis in culture by generating distinct functional cellular entities. These two processes are profoundly different and their outcomes should be considered given the beneficial or possible detrimental effects of MSC-based therapeutic applications.

Lipopolysaccharide (LPS) Promotes Apoptosis in Human Breast Epithelial × Breast Cancer Hybrids, but Not in Parental Cells.

Toll-like receptors (TLRs) belong to the group of pathogen recognition receptors known to play a crucial role in the innate immune system. In cancer, TLR expression is still debated controversially due to contradictory results reporting that both induction of apoptosis as well as tumor progression could depend on TLR signaling, whereby recent data rather indicate a pro-tumorigenic effect. The biological phenomenon of cell fusion has been associated with cancer progression due to findings revealing that fusion-derived hybrid cells could exhibit properties like an increased metastatogenic capacity and an increased drug resistance. Thus, M13MDA435 hybrid cell lines, which derived from spontaneous fusion events between human M13SV1-EGFP-Neo breast epithelial cells and human MDA-MB-435-Hyg breast cancer cells, were investigated. Cultivation of cells in the presence of the TLR4 ligand LPS potently induced apoptosis in all hybrid clones, but not in parental cells, which was most likely attributed to differential kinetics of the TLR4 signal transduction cascade. Activation of this pathway concomitant with NF-κB nuclear translocation and TNF-α expression was solely observed in hybrid cells. However, induction of LPS mediated apoptosis was not TNF-α dependent since TNF-α neutralization was not correlated to a decreased amount of dead cells. In addition to TNF-α, LPS also caused IFN-ß expression in hybrid clones 1 and 3. Interestingly, hybrid clones differ in the mode of LPS induced apoptosis. While neutralization of IFN-ß was sufficient to impair the LPS induced apoptosis in M13MDA435-1 and -3 hybrids, the amount of apoptotic M13MDA435-2 and -4 hybrid cells remained unchanged in the presence of neutralizing IFN-ß antibodies. In summary, the fusion of non-LPS susceptible parental human breast epithelial cells and human breast cancer cells gave rise to LPS susceptible hybrid cells, which is in view with the cell fusion hypothesis that hybrid cells could exhibit novel properties.

Hepatitis B virus infection and replication in a new cell culture system established by fusing HepG2 cells with primary human hepatocytes.

BACKGROUND: Hepatitis B virus (HBV) infection is strictly species and tissue specific, therefore none of the cell models established previously can reproduce the natural infection process of HBV in vitro. The aim of this study was to establish a new cell line that is susceptible to HBV and can support the replication of HBV. METHODS: A hybrid cell line was established by fusing primary human hepatocytes with HepG2 cells. The hybrid cells were incubated with HBV-positive serum for 12 hours. HBV DNA was detected by quantitative fluorescence polymerase chain reaction (QF-PCR). HBsAg (surface antigen) and HBeAg (extracellular form of core antigen) were observed by electrochemiluminescence (ECL). HBcAg (core antigen) was detected by the indirect immunofluorescence technique. HBV covalently closed circular DNA (cccDNA) was analyzed by Southern blot hybridization and quantified using real-time PCR. RESULTS: A new cell line was established and named HepCHLine-7. The extracellular HBV DNA was observed from Day 2 and the levels ranged from 9.80 (± 0.32) × 10(2) copies/mL to 3.12 (± 0.03) × 10(4) copies/mL. Intracellular HBV DNA was detected at Day 2 after infection and the levels ranged from 7.92 (± 1.08) × 10(3) copies/mL to 5.63 (± 0.11) × 10(5) copies/mL. HBsAg in the culture medium was detected from Day 4 to Day 20. HBeAg secretion was positive from Day 5 to Day 20. HBcAg constantly showed positive signals in approximately 20% (± 0.82%) of hybrid cells. Intracellular HBV cccDNA could be detected as early as 2 days postinfection and the highest level was 15.76 (± 0.26) copies/cell. CONCLUSION: HepCHLine-7 cells were susceptible to HBV and supported the replication of HBV. They are therefore suitable for studying the complete life cycle of HBV.

State of the art in cell-cell fusion.

Mammalian life begins with a cell-cell fusion event, i.e. the fusion of the spermatozoid with the oocyte and needs further cell-cell fusion processes for the development, growth, and maintenance of tissues and organs over the whole life span. Furthermore, cellular fusion plays a role in infection, cancer, and stem cell-dependent regeneration as well as including an expanded meaning of partial cellular fusion, nanotube formation, and microparticle-cell fusion. The cellular fusion process is highly regulated by proteins which carry the information to organize and regulate membranes allowing the merge of two separate lipid bilayers into one. The regulation of this genetically and epigenetically controlled process is achieved by different kinds of signals leading to communication of fusing cells. The local cellular and extracellular environment additionally initiates specific cell signaling necessary for the induction of the cell-cell fusion process. Common motifs exist in distinct cell-cell fusion processes and their regulation. However, there is specific regulation of different cell-cell fusion processes, e.g. myoblast, placental, osteoclast, and stem cell fusion. Hence, specialized fusion events vary between cell types and species. Molecular mechanisms remain largely unknown, especially limited knowledge is present for cancer and stem cell fusion mechanisms and regulation. More research is necessary for the understanding of cellular fusion processes which can lead to development of new therapeutic strategies grounding on cellular fusion regulation.

Fusion of mesenchymal stem cells and islet cells for cell therapy.

Auxiliary use of mesenchymal stem/stromal cells (MSCs) to islet transplantation is shown to enhance efficacy. We hypothesized cell fusion of islet cells and MSCs may provide a new cell source with robustness of MSCs and islet cell function. We succeeded electrofusion between dispersed islet cells and MSCs in rats and fused cells sustained beta-cell function in vitro and in vivo, suggesting their possibility of therapeutic application. Here, we describe our method of cell fusion that enabled us to fuse islet cells to MSCs.

Deformability-based microfluidic cell pairing and fusion.

We present a microfluidic cell pairing device capable of sequential trapping and pairing of hundreds of cells using passive hydrodynamics and flow-induced deformation. We describe the design and operation principles of our device and show its applicability for cell fusion. Using our device, we achieved both homotypic and heterotypic cell pairing, demonstrating efficiencies up to 80%. The platform is compatible with fusion protocols based on biological, chemical and physical stimuli with fusion yields up to 95%. Our device further permits its disconnection from the fluidic hardware enabling its transportation for imaging and culture while maintaining cell registration on chip. Our design principles and cell trapping technique can readily be applied for different cell types and can be extended to trap and fuse multiple (>2) cell partners as demonstrated by our preliminary experiments.

The adult livers of immunodeficient mice support human hematopoiesis: evidence for a hepatic mast cell population that develops early in human ontogeny.

The liver plays a vital role in hematopoiesis during mammalian prenatal development but its hematopoietic output declines during the perinatal period. Nonetheless, hepatic hematopoiesis is believed to persist into adulthood. We sought to model human adult-liver hematopoiesis by transplantation of fetal and neonatal hematopoietic stem cells (HSCs) into adult immunodeficient mice. Livers were found to be engrafted with human cells consisting primarily of monocytes and B-cells with lesser contributions by erythrocytes, T-cells, NK-cells and mast-cells. A resident population of CD117(++)CD203c(+) mast cells was also documented in human midgestation liver, indicating that these cells comprise part of the liver's resident immune cell repertoire throughout human ontogeny. The murine liver was shown to support human multilineage hematopoiesis up to 321 days after transplant. Evidence of murine hepatic hematopoiesis was also found in common mouse strains as old as 2 years. Human HSC engraftment of the murine liver was demonstrated by detection of high proliferative-potential colony-forming cells in clonal cultures, observation of CD38-CD34(++) and CD133(+)CD34(++) cells by flow cytometry, and hematopoietic reconstitution of secondary transplant recipients of chimeric liver cells. Additionally, chimeric mice with both hematopoietic and endothelial reconstitution were generated by intrasplenic injection of immunodeficient mice with liver specific expression of the urokinase-type plasminogen activator (uPA) transgene. In conclusion, the murine liver is shown to be a hematopoietic organ throughout adult life that can also support human hematopoiesis in severely immunodeficient strains. Further humanization of the murine liver can be achieved in mice harboring an uPA transgene, which support engraftment of non-hematopoietic cells types. Thus, offering a model system to study the interaction of diverse human liver cell types that regulate hematopoiesis and immune function in the liver.

Functional evaluation of ES-somatic cell hybrids in vitro and in vivo.

Embryonic stem cells (ESCs) have previously been reported to reprogram somatic cells following fusion. The resulting ES-somatic cell hybrids have been shown to adopt the transcriptional profile of ESCs, suggesting that the pluripotent program is dominant. ES-somatic cell hybrids have most characteristics of pluripotent cells in vitro; however, it remains unclear whether the somatic genome is an active partner in the hybrid cells or simply retained predominately as silent cargo. Furthermore, the functional properties of ES-somatic cell hybrids in vivo have been limited to studies on their contribution to teratomas and developing embryos/chimeras. The extent of their pluripotency remains largely unclear. Here we determined that the somatic genome is actively transcribed by generating ES-somatic cell hybrids using Rag2-deficient ESCs fused to autologous wild-type somatic cells. Rag2 expression was detected during in vitro differentiation, suggesting that the somatic genome follows the correct temporal cues during differentiation. Furthermore, ES-somatic cell hybrids maintain their tetraploid state following 4 weeks of differentiation in vivo and are immune tolerated when transferred into matched individuals. The ES-somatic cell hybrids can efficiently differentiate into hematopoietic precursors in both myeloid and lymphoid lineages in vitro, suggesting that the somatic genome is actively transcribed following cell fusion based reprogramming. However, the ES-somatic cell hybrids showed an altered hematopoietic potential following in vitro differentiation and were unable to show hematopoietic engraftment in a mouse model.

Unrepaired DNA damage facilitates elimination of uniparental chromosomes in interspecific hybrid cells.

Elimination of uniparental chromosomes occurs frequently in interspecific hybrid cells. For example, human chromosomes are always eliminated during clone formation when human cells are fused with mouse cells. However, the underlying mechanisms are still elusive. Here, we show that the elimination of human chromosomes in human-mouse hybrid cells is accompanied by continued cell division at the presence of DNA damage on human chromosomes. Deficiency in DNA damage repair on human chromosomes occurs after cell fusion. Furthermore, increasing the level of DNA damage on human chromosomes by irradiation accelerates human chromosome loss in hybrid cells. Our results indicate that the elimination of human chromosomes in human-mouse hybrid cells results from unrepaired DNA damage on human chromosomes. We therefore provide a novel mechanism underlying chromosome instability which may facilitate the understanding of carcinogenesis.

Molecular and bioenergetic differences between cells with African versus European inherited mitochondrial DNA haplogroups: implications for population susceptibility to diseases.

The geographic origins of populations can be identified by their maternally inherited mitochondrial DNA (mtDNA) haplogroups. This study compared human cybrids (cytoplasmic hybrids), which are cell lines with identical nuclei but mitochondria from different individuals with mtDNA from either the H haplogroup or L haplogroup backgrounds. The most common European haplogroup is H while individuals of maternal African origin are of the L haplogroup. Despite lower mtDNA copy numbers, L cybrids had higher expression levels for nine mtDNA-encoded respiratory complex genes, decreased ATP (adenosine triphosphate) turnover rates and lower levels of reactive oxygen species production, parameters which are consistent with more efficient oxidative phosphorylation. Surprisingly, GeneChip arrays showed that the L and H cybrids had major differences in expression of genes of the canonical complement system (5 genes), dermatan/chondroitin sulfate biosynthesis (5 genes) and CCR3 (chemokine, CC motif, receptor 3) signaling (9 genes). Quantitative nuclear gene expression studies confirmed that L cybrids had (a) lower expression levels of complement pathway and innate immunity genes and (b) increased levels of inflammation-related signaling genes, which are critical in human diseases. Our data support the hypothesis that mtDNA haplogroups representing populations from different geographic origins may play a role in differential susceptibilities to diseases.