Design and validation of a medical robotic device system to control two collaborative robots for ultrasound-guided needle insertions.

The percutaneous biopsy is a critical intervention for diagnosis and staging in cancer therapy. Robotic systems can improve the efficiency and outcome of such procedures while alleviating stress for physicians and patients. However, the high complexity of operation and the limited possibilities for robotic integration in the operating room (OR) decrease user acceptance and the number of deployed robots. Collaborative systems and standardized device communication may provide approaches to overcome named problems. Derived from the IEEE 11073 SDC standard terminology of medical device systems, we designed and validated a medical robotic device system (MERODES) to access and control a collaborative setup of two KUKA robots for ultrasound-guided needle insertions. The system is based on a novel standard for service-oriented device connectivity and utilizes collaborative principles to enhance user experience. Implementing separated workflow applications allows for a flexible system setup and configuration. The system was validated in three separate test scenarios to measure accuracies for 1) co-registration, 2) needle target planning in a water bath and 3) in an abdominal phantom. The co-registration accuracy averaged 0.94 ± 0.42 mm. The positioning errors ranged from 0.86 ± 0.42 to 1.19 ± 0.70 mm in the water bath setup and from 1.69 ± 0.92 to 1.96 ± 0.86 mm in the phantom. The presented results serve as a proof-of-concept and add to the current state of the art to alleviate system deployment and fast configuration for percutaneous robotic interventions.

Practical setting and potential applications of interventions guided by PET/MRI.

Multimodality imaging has emerged from a vision thirty years ago to routine clinical use today. Positron emission tomography (PET)/magnetic resonance imaging (MRI) is still relatively new in this arena and particularly suitable for clinical research and technical development. PET/MRI-guidance for interventions opens up opportunities for novel treatments but at the same time demands certain technical and organizational requirements to be fulfilled. In this work, we aimed to demonstrate a practical setting and potential application of PET/MRI guidance of interventional procedures. The superior quantitative physiologic information of PET, the various unique imaging characteristics of MRI, and the reduced radiation exposure are the most relevant advantages of this technique. As a noninvasive interventional tool, focused ultrasound (FUS) ablation of tumor cells would benefit from PET/MRI for diagnostics, treatment planning and intervention. Yet, technical limitations might impeed preclinical research, given that PET/MRI sites are per se not designed as interventional suites. Nonetheless, several approaches have been offered in the past years to upgrade MRI suites for interventional purposes. Taking advantage of state of the art and easy-to-use technology it is possible to create a supporting infrastructure that is suitable for broad preclinical adaption. Several aspects are to be addressed, including remote control of the imaging system, display of the imaging results, communication technology, and implementation of additional devices such as a FUS platform and an MR-compatible robotic system for positioning of the FUS equipment. Feasibility could be demostrated with an examplary experimental setup for interventional PET/MRI. Most PET/MRI sites could allow for interventions with just a few add-ons and modifications, such as comunication, in room image display and sytems control. By unlocking this feature, and driving preclinical research in interventional PET/MRI, translation of the protocol and methodology into clinical settings seems feasible.

Effect of clinical signs, endocrinopathies, timing of surgery, hyperlipidemia, and hyperbilirubinemia on outcome in dogs with gallbladder mucocele.

Gallbladder mucocele (GBM) is a common extra-hepatic biliary syndrome in dogs with death rates ranging from 7 to 45%. Therefore, the aim of this study was to identify the association of survival with variables that could be utilized to improve clinical decisions. A total of 1194 dogs with a gross and histopathological diagnosis of GBM were included from 41 veterinary referral hospitals in this retrospective study. Dogs with GBM that demonstrated abnormal clinical signs had significantly greater odds of death than subclinical dogs in a univariable analysis (OR, 4.2; 95% CI, 2.14-8.23; P<0.001). The multivariable model indicated that categorical variables including owner recognition of jaundice (OR, 2.12; 95% CI, 1.19-3.77; P=0.011), concurrent hyperadrenocorticism (OR 1.94; 95% CI, 1.08-3.47; P=0.026), and Pomeranian breed (OR, 2.46; 95% CI 1.10-5.50; P=0.029) were associated with increased odds of death, and vomiting was associated with decreased odds of death (OR, 0.48; 95% CI, 0.30-0.72; P=0.001). Continuous variables in the multivariable model, total serum/plasma bilirubin concentration (OR, 1.03; 95% CI, 1.01-1.04; P<0.001) and age (OR, 1.17; 95% CI, 1.08-1.26; P<0.001), were associated with increased odds of death. The clinical utility of total serum/plasma bilirubin concentration as a biomarker to predict death was poor with a sensitivity of 0.61 (95% CI, 0.54-0.69) and a specificity of 0.63 (95% CI, 0.59-0.66). This study identified several prognostic variables in dogs with GBM including total serum/plasma bilirubin concentration, age, clinical signs, concurrent hyperadrenocorticism, and the Pomeranian breed. The presence of hypothyroidism or diabetes mellitus did not impact outcome in this study.

DCE-MRI of the breast in a stand-alone setting outside a complementary strategy - results of the TK-study.

OBJECTIVES: To evaluate the accuracy of MRI of the breast (DCE-MRI) in a stand-alone setting with extended indications. MATERIALS AND METHODS: According to the inclusion criteria, breast specialists were invited to refer patients to our institution for DCE-MRI. Depending on the MR findings, patients received either a follow-up or biopsy. Between 04/2006 and 12/2011 a consecutive total of 1,488 women were prospectively examined. RESULTS: Of 1,488 included patients, 393 patients were lost to follow-up, 1,095 patients were evaluated. 124 patients were diagnosed with malignancy by DCE-MRI (76 TP, 48 FP, 971 TN, 0 FN cases). Positive cases were confirmed by histology, negative cases by MR follow-ups or patient questionnaires over the next 5 years in 1,737 cases (sensitivity 100 %; specificity 95.2 %; PPV 61.3 %; NPV 100 %; accuracy 95.5 %). For invasive cancers only (DCIS excluded), the results were 63 TP; 27 FP; 971 TP and 0 FN (sensitivity 100 %; specificity 97.2 %; PPV 70 %; NPV 100 %; accuracy 97.5 %). CONCLUSION: The DCE-MRI indications tested imply that negative results in DCE-MRI reliably exclude cancer. The results were achieved in a stand-alone setting (single modality diagnosis). However, these results are strongly dependent on reader experience and adequate technical standards as prerequisites for optimal diagnoses. KEY POINTS: • DCE-MRI of the breast has a high accuracy in finding breast cancer. • The set of indications for DCE-MRI of the breast is still very limited. • DCE-MRI can achieve a high accuracy in a 'screening-like' setting. • Accuracy of breast DCE-MRI is strongly dependent on technique and reader experience. • A negative DCE-MRI effectively excludes cancer.

Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight.

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology to climate science, yet these properties are surprisingly difficult to measure in the particles' native environment. Electron microscopy requires collection of particles on a substrate; visible light scattering provides insufficient resolution; and X-ray synchrotron studies have been limited to ensembles of particles. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins, vibrational energy transfer by the hydrodynamic interaction of amino acids, and large-scale production of nanoscale structures by flame synthesis.

Femtosecond dark-field imaging with an X-ray free electron laser.

The emergence of femtosecond diffractive imaging with X-ray lasers has enabled pioneering structural studies of isolated particles, such as viruses, at nanometer length scales. However, the issue of missing low frequency data significantly limits the potential of X-ray lasers to reveal sub-nanometer details of micrometer-sized samples. We have developed a new technique of dark-field coherent diffractive imaging to simultaneously overcome the missing data issue and enable us to harness the unique contrast mechanisms available in dark-field microscopy. Images of airborne particulate matter (soot) up to two microns in length were obtained using single-shot diffraction patterns obtained at the Linac Coherent Light Source, four times the size of objects previously imaged in similar experiments. This technique opens the door to femtosecond diffractive imaging of a wide range of micrometer-sized materials that exhibit irreproducible complexity down to the nanoscale, including airborne particulate matter, small cells, bacteria and gold-labeled biological samples.

Fatigue in multiple sclerosis: an example of cytokine mediated sickness behaviour?

BACKGROUND: Fatigue is a major complaint of multiple sclerosis (MS) patients. However, little is known about its pathophysiological mechanisms. Evidence from chronic fatigue syndrome and studies on sickness behaviour suggest that immune and neuroendocrine factors may play a causative role in the development of fatigue. METHODS: We compared whole blood stimulatory capacity for pro- (TNFalpha, IFNgamma) and anti-inflammatory cytokines (IL-10) as well as hypothalamo-pituitary-adrenal (HPA) axis function in 15 MS patients with marked fatigue and 15 patients without fatigue as determined by the Fatigue Severity Scale (FSS). RESULTS: Proinflammatory cytokines were significantly higher (TNFalpha: 478.9 v 228.2 pg/ml, p = 0.01; IFNgamma: 57.6 v 27.8 pg/ml; p = 0.01) in MS patients with fatigue. Furthermore, TNFalpha values significantly correlated with daytime sleepiness as measured by the Epworth Sleepiness Scale (r = 0.64, p = 0.001). Controlling for disease activity (as measured by the Cambridge Multiple Sclerosis Basic Score), disease duration, Expanded Disability Status Scale, and depression further increased the correlation of cytokine production and fatigue. HPA axis activity was not related to fatigue but was modestly correlated with cognitive impairment. CONCLUSION: Our data suggest that fatigue in MS is at least partially mediated through activation of proinflammatory cytokines. In line with earlier findings, HPA axis dysfunction seems not to be relevant in MS fatigue pathogenesis but appears to be linked to cognitive impairment. Our findings suggest that increased levels of inflammatory cytokines may be involved in MS fatigue. Investigation of cytokine profiles may increase the understanding of fatigue pathogenesis in MS.

The release of microparticles by apoptotic cells and their effects on macrophages.

Microparticles are small membrane vesicles released from the cell membrane by exogenous budding. To elucidate the interactions of microparticles with macrophages, the effect of microparticles released from Jurkat T cells on RAW 264.7 cells was determined. Microparticles were isolated by differential centrifugation, using FACS analysis with annexin V and cell surface markers for identification. Various inducers of apoptosis increased the release of microparticles from Jurkat cells up to 5-fold. The released microparticles were then cultured with RAW 264.7 cells. As shown by confocal microscopy and FACS analysis, RAW 264.7 macrophages cleared microparticles by phagocytosis. In addition, microparticles induced apoptosis in RAW 264.7 cells in a dose-dependent manner with up to a 5-fold increase of annexin V positive cells and 9-fold increase in caspase 3 activity. Cell proliferation as determined by the MTT test was also reduced. Furthermore, microparticles stimulated the release of microparticles from macrophages. These effects were specific for macrophages, since no apoptosis was observed in NIH 3T3 and L929 cells. These findings indicate that microparticles can induce macrophages to undergo apoptosis, in turn resulting in a further increase of microparticles. The release of microparticles from apoptotic cells may therefore represent a novel amplification loop of cell death.

Release of DNA from dead and dying lymphocyte and monocyte cell lines in vitro.

DNA is a nuclear macromolecule that circulates in the blood where its levels can reflect the activity of inflammatory and malignant diseases. While dead and dying cells have usually been considered the source of blood DNA, the mechanisms for its release during apoptosis and necrosis are not well defined. To elucidate DNA release, an in vitro model system was used, assessing DNA in the media of living, apoptotic or necrotic Jurkat and U937 cells. Apoptosis was induced by etoposide, camptothecin or staurosporine, while necrosis was induced by heating at 56 degrees C. DNA release was measured by fluorometry with the dye PicoGreen while the extent of death was measured by fluorescence-activated cell sorter analysis with propidium iodide and annexin. Apoptotic Jurkat cells released significantly more DNA in the media than untreated cells while necrotic cells did not show significant DNA release. U937 cells showed similar findings. Pretreatment of Jurkat cells with z-VAD-fmk, a caspase inhibitor, reduced both apoptosis and DNA release. By gel electrophoresis, extracellular DNA from apoptotic cells showed laddering with low molecular weight fragments. These studies suggest that extracellular release of DNA is a consequence of apoptosis and may account for some of the DNA in the blood.

Host response to infection: the role of CpG DNA in induction of cyclooxygenase 2 and nitric oxide synthase 2 in murine macrophages.

Depending on sequence, bacterial and synthetic DNAs can activate the host immune system and influence the host response to infection. The purpose of this study was to determine the abilities of various phosphorothioate oligonucleotides with cytosine-guanosine-containing motifs (CpG DNA) to activate macrophages to produce nitric oxide (NO) and prostaglandin E(2) (PGE(2)) and to induce expression of NO synthase 2 (NOS2) and cyclooxygenase 2 (COX2). As little as 0.3 microg of CpG DNA/ml increased NO and PGE(2) production in a dose- and time-dependent fashion in cells of the mouse macrophage cell line J774. NO and PGE(2) production was noted by 4 to 8 h after initiation of cultures with the CpG DNA, with the kinetics of NO production induced by CpG DNA being comparable to that induced by a combination of lipopolysaccharide and gamma interferon. CpG DNA-treated J774 cells showed enhanced expression of NOS2 and COX2 proteins as determined by immunoblotting, with the relative potencies of the CpG DNAs generally corresponding to those noted for the induction of NO and PGE(2) production as well as to those noted for the induction of interleukin-6 (IL-6), IL-12, and tumor necrosis factor. Extracts from CpG DNA-treated cells converted L-arginine to L-citrulline, but the NOS inhibitor N(G)-monomethyl-L-arginine (NMMA) inhibited this reaction. The COX2-specific inhibitor NS398 inhibited CpG DNA-induced PGE(2) production and inhibited NO production to various degrees. The NOS inhibitors NMMA, 1400W, and N-iminoethyl-L-lysine effectively blocked NO production and increased the production of PGE(2) in a dose-dependent fashion. Thus, analogues of microbial DNA (i.e., CpG DNA) activate mouse macrophage lineage cells for the expression of NOS2 and COX2, with the production of NO and that of PGE(2) occurring in an interdependent manner.

Secretion of whey acidic protein and cystatin is down regulated at mid-lactation in the red kangaroo (Macropus rufus).

Milk collected from the red kangaroo (Macropus rufus) between day 100 and 260 of lactation showed major changes in milk composition at around day 200 of lactation, the time at which the pouch young begins to temporarily exit the pouch and eat herbage. The carbohydrate content of milk declined abruptly at this time and although there was only a small increase in total protein content, SDS PAGE analysis of milk revealed asynchrony in the secretory pattern of individual proteins. The levels of alpha-lactalbumin, beta-lactoglobulin, serum albumin and transferrin remain unchanged during lactation. In contrast, the protease inhibitor cystatin, and the putative protease inhibitor whey acidic protein (WAP) first appeared in milk at elevated concentrations after approximately 150 days of lactation and then ceased to be secreted at approximately 200 days. In addition, a major whey protein, late lactation protein, was first detected in milk around the time whey acidic protein and cystatin cease to be secreted and was present at least until day 260 of lactation. The co-ordinated, but asynchronous secretion of putative protease inhibitors in milk may have several roles during lactation including tissue remodelling in the mammary gland and protecting specific proteins in milk required for physiological development of the dependent young.

The role of the macrophage scavenger receptor in immune stimulation by bacterial DNA and synthetic oligonucleotides.

To assess the role of the macrophage scavenger receptor type A (SRA) in immune activation by CpG DNA, cytokine induction and DNA uptake were tested in vitro and in vivo using SRA knockout (SRA-/-) and wild type (WT) mice. As a source of CpG DNA, Escherichia coli DNA (EC DNA) and a 20-mer phosphorothioate oligodeoxynucleotide with two CpG motifs (CpG ODN) were used. In vitro, both EC DNA and the CpG ODN induced dose-dependent increases of interleukin (IL)-12 production by spleen cells and bone-marrow-derived macrophages (BMMPhi) from both SRA-/- and WT mice. The levels of cytokines produced by SRA-/- spleen cells and BMMPhi were similar to those of WT spleen cells and BMMPhi. When injected intravenously with CpG ODN and EC DNA, both SRA-/- and WT mice showed elevated serum levels of IL-12. To investigate further the role of the SRA, flow cytometry and confocal microscopy were performed to examine the uptake of fluorescently labelled oligonucleotides. SRA-/- and WT BMMPhi showed similarity in the extent of uptake and distribution of oligonucleotides as assessed by these two techniques. Together, these findings indicate that, while the SRA may bind DNA, this receptor is not essential for the uptake of CpG DNA or its immunostimulatory activity.

The role of surface ig binding in the activation of human B cells by phosphorothioate oligodeoxynucleotides.

Phosphorothioate oligodeoxynucleotides (sODNs) can induce T-cell-independent polyclonal activation of human B cells by a mechanism that depends on both sequence and back-bone structure. Because matrix-bound as well as soluble sODNs are mitogenic, this stimulation may result from the engagement of surface receptor(s). In order to investigate whether surface immunoglobin (Ig) could be a receptor for sODNs, the interaction of sODNs-fluorescein isothiocyanate (FITC) with Ig-coated beads was examined. sODNs specifically bound to human IgM and IgG. Moreover, binding of sODN to human B cells induced temperature-dependent capping of bound receptors and colocalization of FITC-sODN and IgM into aggregated caps on the surface of human B cells. A role of surface Ig was furthermore shown by observations that antibody-mediated capping of B-cell surface IgM or IgD inhibited subsequent binding of sODNs and that the capacity of sODN to stimulate human B cells was blocked by excess IgM or IgG, by nonstimulatory antibodies to sIgM, as well as by a variety of negatively charged molecules. Together, these results indicate that sODNs engage surface Ig by charge-charge interactions that lead to activation of human B cells.

Inhibition of murine macrophage IL-12 production by natural and synthetic DNA.

DNA is a complex macromolecule whose immunological properties vary with sequence and structure. To determine whether DNA can inhibit immune responses, the effects of mammalian DNA and synthetic phosphodiester (Po) and phosphorothioate (Ps) oligonucleotides (ODNs) on IL-12 production were tested using murine macrophages. With bacterial DNA as a stimulant, calf thymus DNA and human placenta DNA blocked IL-12 production by splenic and bone marrow macrophages. A (dG)(30) Po ODN and all single-base Ps 30 mer ODNs were also effective inhibitors. The Ps ODNs also blocked IL-12 production induced by lipopolysaccharide (LPS) and a stimulatory Ps ODN. With the J774 cell line, single-base Ps ODNs inhibited IL-12 production induced by bacterial DNA, LPS, and a stimulatory Ps ODN. Together, these results indicate that DNA has inhibitory properties, suggesting that mammalian DNA could limit immune activation during inflammation and counteract the effects of bacterial DNA.

The role of cell surface receptors in the activation of human B cells by phosphorothioate oligonucleotides.

Phosphorothioate oligodeoxynucleotides (sODN) containing the CpG motif or TCG repeats induce T cell-independent polyclonal activation of human B cells. To elucidate the mechanism of this response, the role of cell surface receptors was investigated. Sepharose beads coated with stimulatory but not nonstimulatory sODNs induced B cell proliferation comparably with soluble sODNs. The B cell stimulatory activity of Sepharose-bound sODN did not result from free sODN released from the beads since media incubated with coated beads were inactive. Using FITC-labeled sODNs as probes, binding to human B cells could be detected by flow cytometry. Binding was rapid, saturable, initially temperature independent, but with a rapid off-rate. Competition studies indicated that both stimulatory sODNs and minimally stimulatory sODNs bound to the same receptor. By contrast, phosphodiester oligonucleotides with the same nucleotide sequence as sODNs and bacterial DNA inhibited the binding of sODNs to B cells minimally. Charge appeared to contribute to the binding of sODNs to B cells since binding of sODNs was competitively inhibited by negatively charged molecules, including fucoidan, poly I, and polyvinyl sulfate. These data indicate that human B cells bind sODNs by a receptor-mediated mechanism that is necessary but not sufficient for polyclonal activation.

Influence of backbone chemistry on immune activation by synthetic oligonucleotides.

Depending on base sequence, DNA displays immunological activities relevant to the design of novel therapeutic agents. To determine the influence of backbone structure on these activities, we tested a series of synthetic phosphodiester and phosphorothioate oligonucleotides in in vitro cultures of murine spleen cells. These compounds were 30 bases long and consisted of either a single base or an immunostimulatory sequence (AACGTT) flanked on 5' and 3' ends by 12 nucleotides of each base. Cell activation was assessed by both thymidine incorporation and expression of cell surface CD69; production of interleukin-6 and interleukin-12 was used as a measure of cytokine stimulation. In these assays, phosphorothioate oligonucleotides induced much higher levels of proliferation, CD69 expression, and cytokine production than the comparable phosphodiester compounds and had activity at lower concentrations. The sequence for optimal stimulation by phosphorothioates varied among responses, however. For example, whereas compounds containing an immunostimulatory sequence all induced similar levels of proliferation and CD69 expression, cytokine production was greatest with compounds with dA and dT flanks. Furthermore, while single base dG oligonucleotides stimulated proliferation as both phosphodiesters and phosphorothioates, they failed to stimulate cytokine production. Together, these findings indicate that base sequence as well as backbone chemistry influence immune activation by synthetic oligonucleotides, with the effects varying among responses. While suggesting differences in the structure-function relationships of nucleic acids in their immune activities, these findings also raise the possibility of the design of agents with specific patterns of immune modulation.

CD26 (dipeptidyl peptidase i.v.) on human T lymphocytes does not mediate adhesion of these cells to endothelial cells or fibroblasts.

We have examined the role of CD26 (dipeptidyl peptidase IV) in the adhesion of resting and activated T lymphocytes to endothelial cells and fibroblasts. For this purpose, we ran a short-time adhesion assay under different strategies: Adhesion of T lymphocytes was determined in the presence of different anti-CD26 monoclonal antibodies, or in the presence of synthetic inhibitors of the enzymatic function of CD26. In addition, the expression of CD26 on T lymphocytes, which were adherent to endothelial cells or fibroblasts, was performed by flow cytometric analysis. We found that the anti-CD26 monoclonal antibodies tested here were not able to inhibit T cell adhesion to monolayers of endothelial cells or fibroblasts. Secondly, synthetic inhibitors of the enzymatic function of CD26 had no effect on the adhesion of T lymphocytes to endothelial cells or fibroblasts. Furthermore, CD26-positive T cells were not accumulated in the adherent population. These results suggest that CD26 on T lymphocytes plays no role in T cell adhesion to endothelial cells or fibroblasts.

Neuropeptide Y in the infundibular nucleus and hypophysis of great apes.

We studied the distribution of neuropeptide Y (NPY) immunoreactivity in the infundibular nucleus and the hypophysis of the chimpanzee, gorilla, and orangutan. Using antibodies developed in rabbit against synthetic porcine NPY, we found numerous NPY-immunoreactive neuronal somata in the infundibular nucleus; this nucleus was also filled with short NPY-positive processes and an abundance of punctate structures that could be indicative of synaptic terminals. Numerous varicose NPY-positive fibers were concentrated in the upper infundibular stem in association with capillary loops of the portal vasculature and with the long portal vessels. Bundles of long varicose fibers ran down the infundibular stem, some appearing to terminate in the lower stem in the vicinity of short portal vessels. The bulbous infundibular process contained only sparsely distributed fibers; they were mostly concentrated near vessels at the border between the infundibular process and the anterior pituitary gland, where the fibers often terminated in a spray-like fashion near blood vessels. No NPY immunoreactivity was seen in the anterior pituitary gland. These results provide anatomical evidence for the release of NPY into the portal vasculature of great apes.

Small-diameter corneal inlay in presbyopic or pseudophakic patients.

We report the results of using the small-diameter corneal inlay to create a bifocal cornea. The inlay was implanted in five eyes in January 1993. At 12 months postoperatively, uncorrected near vision had improved from J4 to better than J2 in four of the five. The results indicate that the corneal inlay improves near vision and is compatible within the cornea.

Antibody-induced modulation of CD26 surface expression.

The ability of different anti-CD26 monoclonal antibodies to modulate the expression of CD26 on human T lymphocytes was investigated. By means of a new non-radioactive method using fluorescein isothiocyanate (FITC)-labelled and unlabelled anti-CD26 monoclonal antibodies and flow cytometry, we measured the internalization and re-expression of CD26 on freshly isolated resting human T lymphocytes. The modulation of CD26 surface expression takes place in primarily CD26+ as well as in CD26- T lymphocytes, indicating the presence of an intracellular CD26 pool. In fact, with two different anti-CD26 monoclonal antibodies (Ta1 and M5) intracellular CD26 was detected out of which newly expressed CD26 might have originated. This intracellular CD26 pool appears to be maintained by continuous translation of CD26 mRNA.