Comparative proliferation of non-rheumatoid and rheumatoid human synovial cells

While normal synovial membrane cells have a very long doubling time, rheumatoid arthritis increases cell turn-over leading to the formation of a pannus. We studied the comparative proliferative behaviour in culture of synoviocytes of rheumatoid (RA) and non-rheumatoid (NR) origin in order to evaluate the usefulness of this model to investigate the drugs used in the treatment of inflammatory diseases. First-passage cultures of cells from patients with clinically defined non-inflammatory joint disease or rheumatoid arthritis were observed for 8 days. In the presence of various combinations of supplemented media, 3H-thymidine incorporation, protein content and cell density were assessed. In addition to a relationship between the fetal calf serum (FCS) concentration and cell growth, it was found that RA cells proliferated more rapidly than NR cells. In 1% FCS, protein content and cell density increased in RA cultures whereas NR synoviocytes accumulated in the quiescent phase. In 5% and 10% FCS, RA cells responded more strongly than NR in terms of protein and DNA synthesis and cell division. After 48 hours of relative FCS deprivation, NR cells abruptly started to proliferate; the response of RA cultures was delayed, but the synoviocytes quickly reached preconfluence.     

Cell surface CCR5 density determines the intensity of T cell migration towards rheumatoid arthritis synoviocytes

As we have recently shown that the number of CCR5 molecules at the cell surface determines the efficiency of its function as a chemokine receptor, we tested the hypothesis that cell surface CCR5 density could influence the intensity of T lymphocyte recruitment into the rheumatoid joint. For this purpose, we established two Jurkat cell line-derived clones that differed only by their cell surface CCR5 densities. We studied their chemotaxis towards TNF-alpha-transduced rheumatoid synoviocytes supernatant. The Jurkat cell subline that expressed the higher cell surface CCR5 density migrated more intensively towards the supernatant of TNF-alpha-transduced synoviocytes than the Jurkat cell subline that expressed a lower surface CCR5 density. Moreover, this migration was blocked by an anti-CCR5 mAb. The CCR5 density on T cell surface, which is constant over time for a given individual, but varies drastically from one individual to another, might thus be a factor determining the intensity of joint inflammation in the course of RA.     

Morphology and functional roles of synoviocytes in the joint

The joint capsule exhibits a unique cellular lining in the luminal surface of the synovial membrane. The synovial intimal cells, termed synoviocytes, are believed to be responsible for the production of synovial fluid components, for absorption from the joint cavity, and for blood/synovial fluid exchanges, but their detailed structure and function as well as pathological changes remain unclear. Two types of synoviocytes, macrophagic cells (type A cells) and fibroblast-like cells (type B cells) have been identified. Type A synoviocytes are non-fixed cells that can phagocytose actively cell debris and wastes in the joint cavity, and possess an antigen-presenting ability. These type A cells, derived from blood-borne mononuclear cells, can be considered resident macrophages (tissue macrophages) like hepatic Kupffer cells. Type B synoviocytes are characterized by the rich existence of rough endoplasmic reticulum, and dendritic processes which form a regular network in the luminal surface of the synovial membrane. Their complex three-dimensional architecture was first revealed by our recent scanning electron microscopy of macerated samples. The type B cells, which are proper synoviocytes, are involved in production of specialized matrix constituents including hyaluronan, collagens and fibronectin for the intimal interstitium and synovial fluid. The proliferative potentials of type B cells in loco are much higher than type A cells, although the transformation of subintimal fibroblasts into type B cells can not be excluded. In some mammals, type B cells show features suggesting endocrine and sensory functions, but these are not recognized in other species. The synoviocytes, which form a discontinuous cell layer, develop both fragmented basement membranes around the cells and junctional apparatus such as desmosomes and gap junctions. For an exact understanding of the mechanism of arthritis, we need to establish the morphological background of synoviocytes as well as their functions under normal conditions.     

Expression and production of the long pentraxin PTX3 in rheumatoid arthritis (RA)

PTX3 is a secreted molecule which consists of a C-terminal domain similar to classical pentraxins (e.g. C-reactive protein (CRP)) and of an unrelated N-terminal domain. Unlike the classical pentraxins, the long pentraxin PTX3 is expressed in response to IL-1beta and tumour necrosis factor-alpha (TNF-alpha), but not to IL-6, in various cell types. The present study was designed to investigate the expression of PTX3 in RA. Dissociated RA and osteoarthritis (OA) type B synoviocytes were cultured in the presence and in the absence of inflammatory cytokines. PTX3 mRNA expression in synoviocytes was evaluated by Northern analysis. PTX3 protein levels in synovial cell cultures and synovial fluid were estimated by ELISA, and PTX3 distribution in synovial tissues by immunohistochemical techniques. OA synoviocytes were induced to express high levels of PTX3 mRNA by TNF-alpha, but not by other cytokines including IL-1beta and IL-6. RA synoviocytes, unlike OA synoviocytes, constitutively expressed high levels of PTX3 in the absence of deliberate stimulation. The constitutive expression of PTX3 in RA synoviocytes was not modified by anti-TNF-alpha antibodies, IL-1 receptor antagonist or a combination of the two agents. In contrast, interferon-gamma and transforming growth factor-beta inhibited PTX3 constitutive expression in RA synoviocytes. The joint fluid from RA patients contained higher levels of immunoreactive PTX3 than controls and the synovial tissue contained endothelial cells and synoviocytes positive for PTX3 by immunohistochemistry. In conclusion, PTX3 may play a role in inflammatory circuits of RA, and its relevance as a marker of disease activity deserves further study.     

不同来源人滑膜细胞体外培养的比较

目的对滑膜细胞分离培养的不同实验方法进行比较研究。方法取患者关节滑膜组织和游离的关节液,分别采用滑膜组织培养法和关节液培养法分离培养细胞,观察滑膜细胞的生长情况。结果采用组织培养法获得的滑膜细胞数量较多,细胞形态典型,增殖较快。关节液培养法培养的滑膜细胞．数量少,增殖慢,培养周期较长,所获得的滑膜细胞均能满足后续实验的需要。结论两种方法各有优缺点,可达到互为补充的效果。在临床上可根据病人的情况进行选择。     

Osteoclastogenesis induced by CHIKV-infected fibroblast-like synoviocytes: A possible interplay between synoviocytes and monocytes/macrophages in CHIKV-induced arthralgia/arthritis

Fibroblast-like synoviocytes are known to migrate from joint to joint and are proposed to be one of the key players in the inflammatory cascade amplification in rheumatoid arthritis patients. In the recent CHIKV epidemic, patients developed arthritis-like syndrome and the synoviocyte is one of the suspected players in CHIKV-induced polyarthritis. Thus, to learn more on this syndrome, the responses of fibroblast-like synoviocytes to chikungunya virus (CHIKV) infection, and the interaction between CHIKV-infected synoviocytes and phagocytes, were investigated. Primary human fibroblast-like synoviocyte (HFLS) cultures were infected with clinical isolates of CHIKV at an MOI of 0.001 pfu/cell. Data indicated that HFLS are permissive to CHIKV replication, generating peak titers of 10⁵–10⁶ pfu/ml. Interestingly, CHIKV-infected HFLS cultures secreted mainly the mediators that are responsible for phagocytes recruitment and differentiation (RANKL, IL-6, IL-8 and MCP-1) but not arthritogenic mediators (TNF-α, IL-1β, MMP-1, MMP-2 or MMP-13). The interaction between CHIKV-infected synoviocytes and phagocytes was studied using UV-irradiated, CHIKV-infected HFLS supernatant. Data revealed that supernatants from CHIKV-infected HFLS cultures not only induced migration of primary human monocytes, but also drove monocytes/macrophages into osteoclast-like cells. These differentiated osteoclast-like cells produced high levels of TNF-α and IL-6, principal mediators of arthritis. This data suggests a potential interplay between infected HFLS and recruiting phagocytes which may responsible for the arthralgia/arthritis in CHIKV-infected patients.     

Overexpression of synoviolin facilitates the formation of a functional synovial biomembrane

Digital flexor tendon repair poses a significant challenge for hand surgeons. Currently, extrasynovial tendon grafts are frequently used in clinical settings to bridge flexor tendon defects. However, the healing process is always accompanied by postoperative adhesion. This is mostly due to the fact that no synovial membrane covers the extrasynovial tendon surface, in contrast to the intrasynovial tendon. In this study, we present an efficient method of developing a functional synovial biomembrane on the surface of the extrasynovial tendon. Synoviocytes were isolated from the knee joint of a Japanese white rabbit. After being infected with lentivirus, the over-expression of synoviolin in these synoviocytes was confirmed by semi-quantitative RT-PCR and western blotting. Cellular proliferation and increased hyaluronic acid secretion were confirmed in the synoviolin over-expressing synoviocytes by MTT-based method, cell cycle assays and ELISA. Furthermore, the synoviolin over-expressing synoviocytes were co-cultured with extrasynovial tendons that were harvested from the hind leg of rabbits. After being co-cultured in vitro for 3 and 7 days, these infected synoviocytes were found to accelerate the formation of a biomembrane on the tendon surface compared to the control group. More importantly, Alcian blue staining confirmed the ability of this cultured biomembrane to produce specific matrices containing acidic carboxyl mucopolysaccharides (mainly hyaluronic acid). All these results demonstrate that the over-expression of synoviolin stimulates the proliferation and HA secretion of synoviocytes and facilitates the formation of a functional synovial biomembrane.     

类风湿关节炎大鼠滑膜细胞的类肿瘤样增生与相关基因表达的关系

目的:探讨佐剂性关节炎(AA)大鼠滑膜细胞的类肿瘤样增生和相关基因表达的机制。方法:将Wistar大鼠随机分两组,每组10只,并应用弗氏完全佐剂诱发大鼠AA实验性模型,定期观测踝关节肿胀度至第40天。分别取AA模型组和正常对照组大鼠踝关节进行组织切片,用HE染色后观察病理学变化。取大鼠膝关节滑膜组织体外进行原代细胞培养,用MTT比色法检测大鼠滑膜细胞的增生。同时采用RTPCR法,检测模型组及正常对照组大鼠滑膜组织中相关基因Cmyc和ODCmRNA的转录水平。结果:①体外培养的AA模型组大鼠关节滑膜细胞的增殖显著高于正常组大鼠(P<0.01),并呈类肿瘤样增生。②AA模型组大鼠关节滑膜组织中,Cmyc和ODCmRNA的转录水平明显高于正常对照大鼠(P<0.01)。结论:AA模型组大鼠关节滑膜细胞的类肿瘤样增生,可能与其相关基因Cmyc和ODCmRNA的转录水平增高有关。     

不同分期骨关节炎滑膜细胞中COX-2 mRNA表达的差异

背景：COX-2基因实际存在于关节成纤维样滑膜细胞里,影响骨关节炎症的发生、发展。阐明不同分期骨关节炎滑膜细胞中COX-2基因表达量的差异对进一步深入了解骨关节炎的发生与发展,以及滑膜细胞在这一过程中的作用,具有重要的理论意义。 目的：分析COX-2 mRNA在不同分期骨关节炎成纤维样滑膜细胞中表达的差异。 方法：收集膝骨关节炎病变滑膜44例及正常滑膜12例,经原代细胞培养生长至4代的成纤维样滑膜细胞用于实验,应用实时荧光定量RT-PCR检测骨关节炎和正常成纤维样滑膜细胞中COX-2 mRNA的表达情况,最后使用2-ΔΔCt方法进行相对定量分析。 结果与结论：COX-2 mRNA在骨关节炎的成纤维样滑膜细胞中的表达明显高于正常成纤维样滑膜细胞 (P < 0.05),其中骨关节炎早期组表达最高,与骨关节炎中期组、晚期组比较差异有显著性意义(P < 0.05),骨关节炎中期组与晚期组中表达量差异无显著性意义(P > 0.05)。结果说明COX-2mRNA可能是骨关节炎症病变过程中的重要生物学指标,且主要起作用于骨关节炎病变早期。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程全文链接：     

Hyperplastic synoviocytes from rats with streptococcal cell wall-induced arthritis exhibit a transformed phenotype that is thymic-dependent and retinoid inhibitable.

It has been suggested that streptococcal cell wall-induced arthritis in LEW/N rats resembles a localized neoplasm consisting of, in part, a proliferative and invasive population of fibroblast-like synoviocytes. To further pursue this concept, the synoviocytes from diseased rats were characterized in situ and in vitro for various parameters of "transformation." The spindle-shaped synoviocytes were found throughout the synovium and were the predominant cell type at sites of invasion of bone and cartilage by synovium. They stained intensely for vimentin, a microfilament prominently expressed in immature and transformed mesenchymal cells. They stained variably for Ia antigens and did not exhibit T cell surface antigens nor did they stain with histochemical stains characteristic of monocytes or granulocytes. Electron microscopy confirmed their fibroblastlike morphology and suggested high grade metabolic activity. In primary culture, the abnormal synoviocytes were adherent, grew rapidly and did not contact inhibit. Moreover, they grew under anchorage-independent conditions. These abnormal growth characteristics were inhibited by all-trans retinoic acid. Finally, explants of the arthritic synovium formed short-lived tumorlike nodules in athymic nude mice. These observations, considered in the context of other data, support the concept that the pathologic process represents a thymic-dependent, nonmalignant, locally invasive inflammatory neoplasm.     

Synovial biology and T cells in rheumatoid arthritis.

Events that occur in rheumatoid arthritis synovial tissues are responsible for the signs and symptoms of joint inflammation and for the eventual destruction of articular and periarticular structures that lead to joint dysfunction and disability. The three most abundant cell populations in RA synovium are synovial macrophages (type A synoviocytes), synovial fibroblasts (type B synoviocytes) and infiltrating T lymphocytes. Other important cell populations include B lymphocytes, dendritic cells, plasma cells, mast cells and osteoclasts. Our current understanding of rheumatoid arthritis is moving beyond previous concepts that view this disease as the consequence of a specific and focused humoral or cellular autoimmune response to a single autoantigen. Rather, a new view of rheumatoid arthritis is emerging, which seeks to understand this disease as the product of pathologic cell-cell interactions occurring within a unique and defined environment, the synovium. T lymphocytes in rheumatoid arthritis synovium interact closely with dendritic cells, the most potent antigen-presenting cell population in the immune system. T cells also interact with monocytes and macrophages and cytokine-activated T cells may be, especially, suited to trigger production of the important cytokine TNFalpha by synovial macrophages. Recent evidence also suggests a potent bidirectional interaction between synovial T cells and synovial fibroblasts, which can lead to activation of both cell types. An important role for synovial B lymphocytes has been emphasized recently, both by experimental data and by results of clinical interventions. B cells in synovium can interact with fibroblasts as well as with other cells of the immune system and their potential role as antigen-presenting cells in the joint is as yet underexplored. Rheumatoid arthritis synovium may be one of the most striking examples of pathologic, organ-specific interactions between immune system cells and resident tissue cell populations. This view of rheumatoid arthritis also leads to the prediction that novel approaches to treatment will more logically target the intercellular communication systems that maintain such interactions, rather than attempt to ablate a single cell population.     

Inhibitory effect of clarithromycin on costimulatory molecule expression and cytokine production by synovial fibroblast-like cells

This study was undertaken to investigate the immunomodulatory effect of clarithromycin against synovial fibroblast-like cells (synoviocytes). Synovial tissue obtained from rheumatoid arthritis (RA) or osteoarthritis (OA) patients was enzymatically digested to separate synoviocytes. The synoviocytes were cultured with or without cytokines in the presence of various concentrations of clarithromycin. The expression of costimulatory molecules was examined on the surface of the synoviocytes, using specific MoAbs and flow cytometry. The production of cytokines by synoviocytes was also measured using an immunoenzymatic assay. Finally, autologous T cells were stimulated by interferon-gamma (IFN-γ)-treated synoviocytes in response to purified protein derivative (PPD). In some experiments, MoAbs specific for costimulatory molecules or clarithromycin were added and ³H-thymidine incorporation was counted. Intercellular adhesion molecule-1 (ICAM-1), LFA-3 and vascular cell adhesion molecule-1 (VCAM-1) were detected on the surface of both RA and OA synoviocytes. However, ICAM-2, B7–1 and B7–2 were not detected, and cytokines failed to induce these molecules. Both spontaneous and up-regulated expression of ICAM-1, LFA-3 and VCAM-1 by IFN-γ, IL-1β or 12-o-tetradecanoyl phorbol 13-acetate (TPA) were markedly suppressed by clarithromycin in a dose-dependent manner at concentrations between 0.1 and 10 μg/ml. The production of IL-1β, IL-6, IL-8, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) but not IL-1α and tumour necrosis factor-alpha (TNF-α) by synoviocytes was detected. Clarithromycin significantly suppressed the production of these cytokines, but did not enhance IL-10 production. Finally, autologous T cells were stimulated by IFN-γ-treated synoviocytes in response to PPD. As clarithromycin suppressed HLA-DR and costimulatory molecule expression was enhanced by IFN-γ, autologous T cell proliferation was markedly inhibited by clarithromycin. Clarithromycin has a considerable immunosuppressive effect on synoviocytes by inhibiting costimulatory molecule expression, cytokine production and antigen-specific T cell proliferation induced by synoviocytes.     

The CD44v7/8 epitope as a target to restrain proliferation of fibroblast-like synoviocytes in rheumatoid arthritis

CD44 is a receptor for the glycosaminoglycan hyaluronan. It exists in a large range of isoforms because of variability in the pattern of glycosylation (both N- and O-linked) and of multiple splice variants. Human fibroblast-like synoviocytes derived from patients with rheumatoid arthritis express certain CD44 splice variants and we have investigated the functional implications of their expression. We found that the rate of proliferation of fibroblast-like synoviocytes expressing the CD44v7/8 epitope (average doubling time 55 hours) exceeds those obtained from the same synovial specimen but lacking this particular epitope (69 hours). Antibodies against CD44v7/8, but not against other exons, inhibit cell proliferation with concomitant induction of the cell cycle inhibitors GADD45, GADD153 and the cyclin-dependent protein-kinase inhibitors p21Waf/Cip. These data show that expression of CD44v7/8 contributes to the transformed phenotype of fibroblast-like synoviocytes. More importantly, they reveal the presence of a target that might be amenable to pharmacological intervention in the treatment of rheumatoid arthritis.     

Biscarbamate cross-linked low molecular weight PEI for delivering IL-1 receptor antagonist gene to synoviocytes for arthritis therapy

Cytoxicity is an essential concern for polyethyleneimine 25 kDa (PEI 25 kDa), a widely reported, highly effective transfection agent used in gene delivery. In our recent experiments, Small molecular weight cross-linked poly(ethylene imine) by biscarbamate linkage (PEI-Bu) (Mn: 3278, Mw: 4289) can reduce target cell apoptosis induced by polycationic transfection, and has almost the same DNA condensation capability as PEI 25 kDa. PEI-Bu showed significantly higher activity and lower cytotoxicity than PEI 25 kDa in transfecting the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1Ra) gene to rat synoviocytes, an optimal target for arthritis treatment. The expression of IL-1Ra in synoviocytes then suppresses the expression of metalloproteases 13 (MMP13) gene, which is responsible for cartilage destruction regulated by IL-1β in arthritis. In conclusion, PEI-Bu is a promising tool for delivering IL-1Ra gene to synoviocytes for arthritis therapy.     

Memory CD8(+) T cells undergo peripheral tolerance

Memory T cells differ from naive T cells in that they respond more rapidly and in greater numbers. In addition, memory T cells are generally believed to be less susceptible to tolerance induction than naive T cells. In this study, we show that this is not the case. Using two different methods of tolerance induction, peptide-induced tolerance and crosstolerance, we present evidence that memory CD8(+) T cells are as susceptible to tolerance as naive cells. These results have a direct impact on manipulating T cell responses to self-antigens in order to improve immunotherapy of cancer and autoimmune diseases.     

Three-dimensional ultrastructure of synoviocytes in the knee joint of rabbits and morphological changes in osteoarthritis model

The synovial intima is composed of two types of synoviocytes: absorptive macrophages and secretory, fibroblast-like F cells. Many studies have tried to observe synoviocytes by scanning electron microscopy (SEM) but failed to reveal the entire shape of synoviocytes because they are deeply embedded in the interstitial matrix. The present study, primarily employing SEM observation of NaOH macerated samples, reveals the distribution and three-dimensional ultrastructure of the synoviocytes in the normal knee joint of rabbits, and the morphological changes of synoviocytes in an osteoarthritis model of this animal. F cells were broadly distributed throughout the synovial intima, while macrophages showed a restricted distribution on fatty tissues around the patella. F cells were classified into a flat type, which covered the surface of synovial membrane like an epithelium, and a dendritic type, which extended long processes to form a characteristic meshwork on the surface. The flat type predominated in regions adhering to the femur, while the dendritic type predominated in ambilateral parts of both the patella and tendon of the musculus quadriceps femoris, and on the peripatellar fatty tissue. Intermediate forms of flat and dendritic types appeared in middle regions between the patella and periphery of the joint capsule. In the synovial membrane of the osteoarthritis model, both types of synoviocytes increased in number and changed their morphology, indicating their elevated activities in absorption and secretion. It is suggested that the ultrastructural changes in synoviocytes reflect pathological conditions of the synovial membrane, and synoviocytes play important roles in the pathogenesis of osteoarthritis.     

Regulation of synoviocyte proliferation, apoptosis, and invasion by the p53 tumor suppressor gene.

Recent studies show that 1) the p53 tumor suppressor protein is overexpressed by rheumatoid arthritis (RA) synovium and fibroblast-like synoviocytes (FLS) and 2) somatic mutations previously identified in human tumors are present in RA synovium and FLS. We have hypothesized that abnormalities in p53 can contribute to chronic destructive RA synovitis. To understand the functional consequences of p53 abnormalities in FLS, RA and normal FLS expressing wild-type p53 were transduced with a retroviral vector encoding the human papilloma virus 18 E6 gene, which inactivates endogenous p53 protein. Three RA and one normal FLS lines were infected with recombinant retrovirus encoding the neomycin resistance gene (neo) or E6+neo. FLS proliferation, apoptosis, and invasion was studied in E6, neo, and uninfected parental strains (PS). The growth rate for E6 was significantly increased with a sixfold increase in cell number after 7 days compared with a twofold to threefold increase in neo and PS. When FLS were treated with cytokines, proliferative response of E6, neo, and PS to interleukin-1 and transforming growth factor-beta were similar. However, response to platelet-derived growth factor was significantly greater in E6 FLS compared with neo or PS. Apoptosis was studied by incubating FLS with sodium nitroprusside as a source of nitric oxide or hydrogen peroxide for 8 hours and examining DNA fragmentation and E6 cells were significantly less susceptible to cell death. In addition, E6 FLS were more invasive into cartilage extracts than neo or PS using an in vitro cell invasion assay. These data suggest that p53 is a critical regulator of FLS proliferation, apoptosis, and invasiveness. Abnormalities of p53 function might contribute to synovial lining expansion and joint destruction in RA.     

Pannocytes: distinctive cells found in rheumatoid arthritis articular cartilage erosions.

A distinctive cell was identified from sites of rheumatoid arthritis cartilage injury. Similar cells are not found in lesions of osteoarthritis cartilage. We have designated them as pannocytes (PCs). Their rhomboid morphology differs from the bipolar shape of fibroblast-like synoviocytes or the spherical configuration of primary human articular chondrocytes. Chondrocytes are short-lived, whereas the original PC line grew for 25 passages before becoming senescent. Features in common with cultured primary chondrocytes include maximal proliferation in response to transforming growth factor-beta a catabolic response to interleukin-1 beta, collagenase production, and mRNA for the induced lymphocyte antigen and inducible nitric oxide synthase. Despite the presence of the inducible nitric oxide synthase message, PCs do not produce NO either constitutively or when cytokine stimulated. Each of the mesenchymal cells, fibroblast-like synoviocytes, primary chondrocytes, and PCs have the gene for type I collagen, but the type II collagen gene is detected only in primary chondrocytes. PCs can be distinguished from fibroblast-like synoviocytes and primary chondrocytes by their morphology, bright VCAM-1 staining, and growth response to cytokines and growth factors. Their prolonged life span in vitro suggests that PCs might represent an earlier stage of mesenchymal cell differentiation, and they could have a heretofore unrecognized role in rheumatoid arthritis joint destruction.     

Susceptibility to DNA damage induced by antibiotics in lymphocytes from malnourished children

Infectious disease and malnutrition in children are public health problems in developing countries. Malnutrition is associated with higher levels of DNA damage, and this increased damage could be due to different factors, including the possibility that cells from malnourished children could be more susceptible to environmental damage. The aim of the present study was to evaluate the susceptibility of lymphocytes from malnourished children to DNA damage induced by antibiotics by using the comet assay. The same group of malnourished infected children were studied before and after a treatment period, and compared to a group of well-nourished infected children. Results showed that before and after drug treatment, tail length migration was two times greater in malnourished than in well-nourished children. The proportion of cells with high damage was also increased in malnourished children. Additionally in well-nourished and malnourished children, a cell subpopulation (non-damaged cells) more resistant to DNA damage induced by antibiotics was observed; this was more prevalent in the well-nourished children. Meanwhile, in malnourished children, a cell population seems to be more susceptible and reaches higher levels of DNA damage. This might help explain the impaired immune response observed in malnourished children. The increased DNA migration and the increased proportion of cells with higher levels of damage seem to indicate that malnourished children are more susceptible to DNA damage induced by drugs.