Use of fluorochromes in the determination of chemotaxis and haptotaxis of granulocytes by micropore filter assays

Targeting the leukocyte activation cascade: getting to the site of inflammation using microfabricated assays

This paper describes the use of microfabricated devices to study the leukocyte activation cascade (LAC). The devices consist of microchannels fabricated in polydimethylsiloxane using soft lithography. Microfluidics, used to generate physiologically relevant levels of shear flow, was achieved by the simple attachment of a syringe pump. Microchannel surfaces were modified by self-assembled monolayer (SAM) chemistries. The devices were adapted to standard 96-well tissue culture format with microchannels that could accommodate either a monolayer of endothelial cells or a SAM with immobilized chemokines. Chemotaxis was performed using linear gradients of chemokine set in a 3D matrix. Using this approach, we demonstrated robust chemotaxis of primary human leukocytes (PHLs) in response to a gradient of the chemokine CCL2. Rolling and adhesion assays performed under shear flow demonstrated that leukocyte recruitment to the substrate was highly sensitive to both biological and physical forces. CCL2 and CXCL12 treatment of PHLs dose dependently increased activation and adhesion. These actions could be inhibited by the use of peptide or small molecule antagonists. These devices provide a robust platform to perform LAC assays under in vivo-like conditions.

Fluorescence-based assays for in vitro analysis of cell adhesion and migration

Cell adhesion and cell migration are two primary cellular phenomena for which in vitro approaches may be exploited to effectively dissect the individual events and underlying molecular mechanisms. The use of assays dedicated to the analysis of cell adhesion and migration in vitro also afford an efficient way of conducting larger basic and applied research screenings on the factors affecting these processes and are potentially exploitable in the context of routine diagnostic, prognostic, and predictive tests in the biological and medical fields. Therefore, there is a longstanding continuum in the interest in devising more rationale such assays and major contributions in this direction have been provided by the advent of procedures based on fluorescence cell tagging, the design of instruments capable of detecting fluorescent signals with high sensitivity, and informatic tools allowing sophisticated elaboration of data generated through these instruments. In this report, we describe three representative fluorescence-based model assays for the qualitative and quantitative assessment of cell adhesion and cell locomotion in static and dynamic conditions. The assays are easily performed, accurate and reproducible, and can be automated for high-to-medium throughput screenings of cell behavior in vitro. Performance of the assays involves the use of certain dedicated disposable accessories, which are commercially available, and a few instruments that, due to their versatility, can be regarded as constituents of a more generic laboratory setup.

Periodic direct current does not promote wound closure in an in vitro dynamic model of cell migration

BACKGROUND AND PURPOSE

A prevailing paradigm is that electrical fields can promote cell migration and tissue healing. To further validate this paradigm, we tested the hypothesis that periodic direct current (DC) can enhance wound closure using an in vitro dynamic model of cell migration.

METHODS AND RESULTS

Layers of primary fibroblasts were wounded and treated with DC under various voltages. Repair area, cell velocity, and directionality as well as lamellipodium area were evaluated at different times. Direct current had no beneficial effect on cell migration. Moreover, prolonged stimulation under the highest voltage led to significant reduction in wound closure and cell velocity. The reduction of membrane protusions in stimulated cells may be associated with the deleterious effect of DC.

DISCUSSION AND CONCLUSION

Contrary to the authors' expectations, they found that periodic DC did not promote wound closure, a finding that emphasizes the need to clarify the complex effects of electrical fields on migrating cells.

Cell migration/invasion assays and their application in cancer drug discovery

Invasive capacity is the single most important trait that distinguishes benign from malignant lesions. Tumour cells, during intravasation and extravasation of blood and lymphatic channels and when establishing colonies at secondary sites, must move through tissue boundaries that normal adult cells (other than, for example activated leukocytes) do not cross. Similar mechanisms are also utilised by activated endothelial cells during the generation of new blood vessels that enable the sustained growth and dissemination of tumours. It is now increasingly recognised that these processes--cell motility and invasion--might provide a rich source of novel targets for cancer therapy and that appropriate inhibitors may restrain both metastasis and neoangiogenesis. This new paradigm demands screening assays that can rapidly and quantitatively measure cell movement and the ability to traverse physiological barriers. We also need to consider whether simple reductionist in vitro approaches can reliably model the complexity of in vivo tumour invasion/neoangiogenesis. There are both opportunities and challenges ahead in developing a balanced portfolio of assays that will be able to evaluate accurately and finally deliver novel anti-invasive agents with therapeutic potential for clinical use.

Lymphotoxin beta-mediated stimulation of synoviocytes in rheumatoid arthritis

OBJECTIVE

Lymphotoxin beta (LTbeta), a cytokine produced by T cells and B cells, plays a central role in the normal development of lymph nodes and is critical in the formation of ectopic germinal center reactions in rheumatoid synovitis. Because resident fibroblast-like synoviocytes (FLS) express receptors for LTbeta, we examined the consequences of FLS activation by LTbeta.

METHODS

FLS from patients with rheumatoid arthritis were isolated and examined for the expression of LTbeta receptor. FLS were incubated with LTalpha1beta2 and assayed for the production of cytokines and chemokines and the up-regulation of adhesion molecules.

RESULTS

Exposure of FLS to recombinant LTalpha1beta2 resulted in the production of multiple inflammatory cytokines and metalloproteinases, implicating FLS as amplifiers of the inflammatory process in the inflamed joint. Additionally, LTalpha1beta2 was found to up-regulate the expression of cell adhesion molecules, rendering FLS to efficient adhesion substrates for T cells. LTalpha1beta2 also induced production of the chemokines CCL2 and CCL5, which elicited transmigration activity of T cells. Upon stimulation with LTalpha1beta2, FLS did not acquire characteristics of follicular dendritic cells.

CONCLUSION

These data document that FLS are involved in multiple stages of the inflammatory process, including the recruitment and retention of lymphocytes in the synovial microenvironment. We propose that the heterotypic interaction between LTbeta-producing lymphocytes and responding FLS contributes to the establishment of complex lymphoid microstructures, and that this may be one element that defines susceptibility of the synovial membrane to lymphoid organogenesis.

Altered biosynthesis of leukotrienes and lipoxins and host defense disorders in patients with cirrhosis and ascites

BACKGROUND & AIMS

Advanced cirrhosis is associated with impaired leukocyte function, but the mechanism underlying this host defense alteration is unknown. The aim of this study was to investigate the lipoxygenase pathway of arachidonic acid metabolism and its influence in leukocyte trafficking in patients with cirrhosis and ascites.

METHODS

Neutrophils (polymorphonuclear leukocytes [PMN]) were isolated from patients with cirrhosis and ascites and healthy subjects, and 5-lipoxygenase (5-LO) messenger RNA levels and 5-LO-derived products were measured. The effect of leukotrienes (LT) and lipoxins (LX) on PMN adhesion and migration was also assessed.

RESULTS

PMN from patients with cirrhosis showed increased 5-LO messenger RNA expression. However, in vitro generation of LTB4, cysteinyl-containing LT and LX was significantly decreased in cirrhotic patients. Interestingly, a close relationship between the activity of the renin-angiotensin system and LXA4 biosynthesis was observed both in vitro and in vivo. PMN isolated from cirrhotic patients with ascites showed significantly decreased adhesion and migration in response to LTB4. LXA4 did not provoke PMN adhesion and migration, but rather abrogated the differences between control and cirrhotic PMN. Cirrhotic monocytes showed marked impairment in adherence to laminin when stimulated with either LTB4 or LXA4.

CONCLUSIONS

These results show the existence of altered biosynthesis of LT and LX and defective response to these lipoxygenase products in leukocytes from patients with cirrhosis and ascites. This abnormality may be relevant to the pathogenesis of host defense disorders in chronic liver disease.