Adhesion of human neutrophils to and activation by type-I collagen involving a beta 2 integrin

Collagen concentration regulates neutrophil extravasation and migration in response to infection in an endothelium dependent manner

Introduction

As the body's first line of defense against disease and infection, neutrophils must efficiently navigate to sites of inflammation; however, neutrophil dysregulation contributes to the pathogenesis of numerous diseases that leave people susceptible to infections. Many of these diseases are also associated with changes to the protein composition of the extracellular matrix. While it is known that neutrophils and endothelial cells, which play a key role in neutrophil activation, are sensitive to the mechanical and structural properties of the extracellular matrix, our understanding of how protein composition in the matrix affects the neutrophil response to infection is incomplete.

Methods

To investigate the effects of extracellular matrix composition on the neutrophil response to infection, we used an infection-on-a-chip microfluidic device that replicates a portion of a blood vessel endothelium surrounded by a model extracellular matrix. Model blood vessels were fabricated by seeding human umbilical vein endothelial cells on 2, 4, or 6 mg/mL type I collagen hydrogels. Primary human neutrophils were loaded into the endothelial lumens and stimulated by adding the bacterial pathogen Pseudomonas aeruginosa to the surrounding matrix.

Results

Collagen concentration did not affect the cell density or barrier function of the endothelial lumens. Upon infectious challenge, we found greater neutrophil extravasation into the 4 mg/mL collagen gels compared to the 6 mg/mL collagen gels. We further found that extravasated neutrophils had the highest migration speed and distance in 2mg/mL gels and that these values decreased with increasing collagen concentration. However, these phenomena were not observed in the absence of an endothelial lumen. Lastly, no differences in the percent of extravasated neutrophils producing reactive oxygen species were observed across the various collagen concentrations.

Discussion

Our study suggests that neutrophil extravasation and migration in response to an infectious challenge are regulated by collagen concentration in an endothelial cell-dependent manner. The results demonstrate how the mechanical and structural aspects of the tissue microenvironment affect the neutrophil response to infection. Additionally, these findings underscore the importance of developing and using microphysiological systems for studying the regulatory factors that govern the neutrophil response.

HIGH THROUGHPUT QUANTITATION OF HUMAN NEUTROPHIL RECRUITMENT AND FUNCTIONAL RESPONSES IN AN AIR-BLOOD BARRIER ARRAY

Dysregulated neutrophil recruitment drives many pulmonary diseases, but most preclinical screening methods are unsuited to evaluate pulmonary neutrophilia, limiting progress towards therapeutics. Namely, high throughput therapeutic screening systems typically exclude critical neutrophilic pathophysiology, including blood-to-lung recruitment, dysfunctional activation, and resulting impacts on the air-blood barrier. To meet the conflicting demands of physiological complexity and high throughput, we developed an assay of 96-well Leukocyte recruitment in an Air-Blood Barrier Array (L-ABBA-96) that enables in vivo -like neutrophil recruitment compatible with downstream phenotyping by automated flow cytometry. We modeled acute respiratory distress syndrome (ARDS) with neutrophil recruitment to 20 ng/mL epithelial-side interleukin 8 (IL-8) and found a dose dependent reduction in recruitment with physiologic doses of baricitinib, a JAK1/2 inhibitor recently FDA-approved for severe COVID-19 ARDS. Additionally, neutrophil recruitment to patient-derived cystic fibrosis sputum supernatant induced disease-mimetic recruitment and activation of healthy donor neutrophils and upregulated endothelial e-selectin. Compared to 24-well assays, the L-ABBA-96 reduces required patient sample volumes by 25 times per well and quadruples throughput per plate. Compared to microfluidic assays, the L-ABBA-96 recruits two orders of magnitude more neutrophils per well, enabling downstream flow cytometry and other standard biochemical assays. This novel pairing of high-throughput in vitro modeling of organ-level lung function with parallel high-throughput leukocyte phenotyping substantially advances opportunities for pathophysiological studies, personalized medicine, and drug testing applications.

Effect of Adhesion and Substrate Elasticity on Neutrophil Extracellular Trap Formation

Neutrophils are the most abundant type of white blood cells. Upon stimulation, they are able to decondense and release their chromatin as neutrophil extracellular traps (NETs). This process (NETosis) is part of immune defense mechanisms but also plays an important role in many chronic and inflammatory diseases such as atherosclerosis, rheumatoid arthritis, diabetes, and cancer. For this reason, much effort has been invested into understanding biochemical signaling pathways in NETosis. However, the impact of the mechanical micro-environment and adhesion on NETosis is not well-understood. Here, we studied how adhesion and especially substrate elasticity affect NETosis. We employed polyacrylamide (PAA) gels with distinctly defined elasticities (Young's modulus E) within the physiologically relevant range from 1 to 128 kPa and coated the gels with integrin ligands (collagen I, fibrinogen). Neutrophils were cultured on these substrates and stimulated with potent inducers of NETosis: phorbol 12-myristate 13-acetate (PMA) and lipopolysaccharide (LPS). Interestingly, PMA-induced NETosis was neither affected by substrate elasticity nor by different integrin ligands. In contrast, for LPS stimulation, NETosis rates increased with increasing substrate elasticity (E > 20 kPa). LPS-induced NETosis increased with increasing cell contact area, while PMA-induced NETosis did not require adhesion at all. Furthermore, inhibition of phosphatidylinositide 3 kinase (PI3K), which is involved in adhesion signaling, completely abolished LPS-induced NETosis but only slightly decreased PMA-induced NETosis. In summary, we show that LPS-induced NETosis depends on adhesion and substrate elasticity while PMA-induced NETosis is completely independent of adhesion.

Silver nanoparticles alter epithelial basement membrane integrity, cell adhesion molecule expression, and TGF-β1 secretion

Silver nanoparticles (AgNPs) are widely used in consumer and pharmaceutical products due to their antipathogenic properties. However, safety concerns have been raised due to their bioactive properties. While reports have demonstrated AgNPs can embed within the extracellular matrix, their effects on basement membrane (BM) production, integrin engagement, and tissue-integrity are not well-defined. This study analyzed the effects of AgNPs on BM production, composition and integrin/focal adhesion interactions in representative lung, esophageal, breast and colorectal epithelia models. A multidisciplinary approach including focused proteomics, QPCR arrays, pathway analyses, and immune-based, structural and functional assays was used to identify molecular and physiological changes in cell adhesions and the BM induced by acute and chronic AgNP exposure. Dysregulated targets included CD44 and transforming growth factor-beta, two proteins frequently altered during pathogenesis. Results indicate AgNP exposure interferes with BM and cell adhesion dynamics, and provide insight into the mechanisms of AgNP-induced disruption of epithelial physiology.

Neutrophils drive accelerated tumor progression in the collagen-dense mammary tumor microenvironment

Background

High mammographic density has been correlated with a 4-fold to 6-fold increased risk of developing breast cancer, and is associated with increased stromal deposition of extracellular matrix proteins, including collagen I. The molecular and cellular mechanisms responsible for high breast tissue density are not completely understood.

Methods

We previously described accelerated tumor formation and metastases in a transgenic mouse model of collagen-dense mammary tumors (type I collagen-α1 (Col1α1)^tm1Jae and mouse mammary tumor virus - polyoma virus middle T antigen (MMTV-PyVT)) compared to wild-type mice. Using ELISA cytokine arrays and multi-color flow cytometry analysis, we studied cytokine signals and the non-malignant, immune cells in the collagen-dense tumor microenvironment that may promote accelerated tumor progression and metastasis.

Results

Collagen-dense tumors did not show any alteration in immune cell populations at late stages. The cytokine signals in the mammary tumor microenvironment were clearly different between wild-type and collagen-dense tumors. Cytokines associated with neutrophil signaling, such as granulocyte monocyte-colony stimulated factor (GM-CSF), were increased in collagen-dense tumors. Depleting neutrophils with anti-Ly6G (1A8) significantly reduced the number of tumors, and blocked metastasis in over 80 % of mice with collagen-dense tumors, but did not impact tumor growth or metastasis in wild-type mice.

Conclusion

Our study suggests that tumor progression in a collagen-dense microenvironment is mechanistically different, with pro-tumor neutrophils, compared to a non-dense microenvironment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-016-0703-7) contains supplementary material, which is available to authorized users.

Pharmacological application of carbon monoxide ameliorates islet-directed autoimmunity in mice via anti-inflammatory and anti-apoptotic effects

AIMS/HYPOTHESIS

Recent studies have identified carbon monoxide (CO) as a potential therapeutic molecule for the treatment of autoimmune diseases owing to its anti-inflammatory and anti-apoptotic properties. We explored the efficacy and the mechanisms of action of the CO-releasing molecule (CORM)-A1 in preclinical models of type 1 diabetes.

METHODS

The impact of CORM-A1 on diabetes development was evaluated in models of spontaneous diabetes in NOD mice and in diabetes induced in C57BL/6 mice by multiple low-dose streptozotocin (MLDS). Ex vivo analysis was performed to determine the impact of CORM-A1 both on T helper (Th) cell and macrophage differentiation and on their production of soluble mediators in peripheral tissues and in infiltrates of pancreatic islets. The potential effect of CORM-A1 on cytokine-induced apoptosis in pancreatic islets or beta cells was evaluated in vitro.

RESULTS

CORM-A1 conferred protection from diabetes in MLDS-induced mice and reduced diabetes incidence in NOD mice as confirmed by preserved insulin secretion and improved histological signs of the disease. In MLDS-challenged mice, CORM-A1 attenuated Th1, Th17, and M1 macrophage response and facilitated Th2 cell differentiation. In addition, CORM-A1 treatment in NOD mice upregulated the regulatory arm of the immune response (M2 macrophages and FoxP3(+) regulatory T cells). Importantly, CORM-A1 interfered with in vitro cytokine-induced beta cell apoptosis through the reduction of cytochrome c and caspase 3 levels.

CONCLUSIONS/INTERPRETATION

The ability of CORM-A1 to protect mice from developing type 1 diabetes provides a valuable proof of concept for the potential exploitation of controlled CO delivery in clinical settings for the treatment of autoimmune diabetes.

A modified collagen gel enhances healing outcome in a preclinical swine model of excisional wounds

Collagen-based dressings are of great interest in wound care. However, evidence supporting their mechanism of action is scanty. This work provides first results from a preclinical swine model of excisional wounds, elucidating the mechanism of action of a modified collagen gel (MCG) dressing. Following wounding, wound-edge tissue was collected at specific time intervals (3, 7, 14, and 21 days postwounding). On day 7, histological analysis showed significant increase in the length of rete ridges, suggesting improved biomechanical properties of the healing wound tissue. Rapid and transient mounting of inflammation is necessary for efficient healing. MCG significantly accelerated neutrophil and macrophage recruitment to the wound site on day 3 and day 7 with successful resolution of inflammation on day 21. MCG induced monocyte chemotactic protein-1 expression in neutrophil-like human promyelocytic leukemia-60 cells in vitro. In vivo, MCG-treated wound tissue displayed elevated vascular endothelial growth factor expression. Consistently, MCG-treated wounds displayed significantly higher abundance of endothelial cells with increased blood flow to the wound area indicating improved vascularization. This observation was explained by the finding that MCG enhanced proliferation of wound-site endothelial cells. In MCG-treated wound tissue, Masson's trichrome and picrosirius red staining showed higher abundance of collagen and increased collagen type I:III ratio. This work presents first evidence from a preclinical setting explaining how a collagen-based dressing may improve wound closure by targeting multiple key mechanisms. The current findings warrant additional studies to determine whether the responses to the MCG are different from other collagen-based products used in clinical setting.

The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.

Gender differences in pulmonary inflammation following systemic cadmium administration in rats

OBJECTIVE

To examine the presence of gender differences in pulmonary inflammation evoked by acute systemic cadmium administration in rats.

METHODS

Presence of basic indicators of lung inflammation (inflammatory cytokine lung content, leukocyte infiltration and activity of cells recovered from lungs by enzyme digestion) was analyzed and compared in animals of the two sexes.

RESULTS

Intraperitoneal administration of cadmium (1.0 mg/kg) resulted in higher cadmium content in lungs of female rats. Higher tumor necrosis factor (TNF) content was noted in lung homogenates of male rats, while interleukin-6 (IL-6) content was slightly, but significantly greater in lungs of female rats. Increased leukocyte infiltration was observed in lungs of male rats, mainly due to neutrophils. Increased responsiveness to phorbol myristate acetate (PMA) stimulation was noted in cells recovered from lungs of male rats. Rise in intracellular content of myeloperoxidase (MPO) was noted in lung cells from cadmium-treated rats of both sexes, but higher in cells from male rats.

CONCLUSIONS

Presented data documented a more intense pulmonary inflammatory response to systemic cadmium administration in males, with higher IL-6 levels in lungs of female individuals. These sex differences in proinflamatory activity of cadmium in lungs should be taken into consideration in studying the remote toxicity of this heavy metal.

Lungs: remote inflammatory target of systemic cadmium administration in rats

Pulmonary inflammation is a biological response to cadmium entering the body via the respiratory route. Systemic administration of this metal revealed the lungs as a significant site of its disposition. In this study, the presence of basic indicators of lung inflammation (leukocyte infiltration and activity of cells recovered from lungs by enzyme digestion) was analyzed in the rat model of acute systemic cadmium intoxication. Intraperitoneal administration of both cadmium doses (0.5mg/kg and 1.0mg/kg) resulted in increased numbers of neutrophils. Signs of spontaneous activation of lung cells including the capacity of reduction of nitroblue tetrazolium (NBT), increase in myeloperoxidase (MPO) intracellular content and increase in interleukin-6 (IL-6) production were noted at both cadmium doses. Increased lung cell responsiveness to stimulation in vitro was noted at the higher cadmium dose. The presence of pulmonary inflammatory parameters in rats administered intraperitoneally with cadmium revealed the lungs as remote inflammatory targets of this metal.

Gender differences in acute cadmium-induced systemic inflammation in rats

OBJECTIVE

To examine the presence of gender differences in pro-inflammatory potential of cadmium in rats by comparing systemic inflammatory response to acute cadmium intoxication in animals of the two sexes.

METHODS

Basic aspects of this response were evaluated, including plasma levels of inflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6) and of major rat acute phase protein alpha 2-macroglobulin (alpha2-M), as soluble indicators of inflammation, and the number and activity of peripheral blood leukocytes, as cellular indicators of inflammation.

RESULTS

Differential increases of IL-6 and alpha2-M (higher in males than in females) in peripheral blood cell counts and types (leukocytosis and shift in the ratio of granulocytes to lymphocytes more pronounced in males vs females) and in levels of neutrophil priming (higher in males vs females) were noted.

CONCLUSION

The data document a more intense inflammatory response to cadmium administration in males. The sex differences in inflammatory effects of cadmium might be taken into consideration in studying the toxicity of this heavy metal.

Extracellular superoxide dismutase in pulmonary fibrosis

Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.

Surface morphology and adsorbed proteins affect phagocyte responses to nano-porous alumina

This study evaluates human neutrophil responses to aluminum oxide membranes with different pore sizes (20 nm and 200 nm in diameter) uncoated and pre-coated with serum, collagen I, or fibrinogen. The effect of released neutrophil granule components on the survival of osteoblastic cells (MG63) bound to the alumina membranes has also been evaluated. Without protein coatings the 20 nm pore-size membranes prompt higher reactive oxygen species (ROS) production as assessed by luminol-amplified chemiluminescence than the 200 nm pore-size membranes. Such pore-size depending responses were also found on membranes pre-coated with fibrinogen, but not with collagen or serum were in fact a much lower ROS production was observed. In addition, uncoated and fibrinogen-coated membranes prompt stronger release of the granule enzymes, myeloperoxidase and elastase, than collagen or serum-coated alumina. Equally important, we found that surface-mediated phagocyte activation and the subsequent release of granule components had a significant affect on the adhesion, viability and proliferation of osteoblasts. This stresses the importance of studying not only cell/surface interactions but also cell/cell interactions in wound healing and tissue regeneration processes.

Association of BAP31 with CD11b/CD18

The beta2 integrin CD11b/CD18 is an integral membrane protein that is present in the plasma membrane and secondary granules of neutrophils and functions as a major adhesion molecule. Upon cellular activation, there is translocation of intracellular pools of CD11b/CD18 to the plasma membrane in concert with enhanced cellular adhesion. Although much is known about the function of CD11b/CD18, how this protein is transported within the cell is less well defined. Here we report that CD11b/CD18 specifically binds to BAP31, a member of a novel class of sorting proteins regulating cellular anterograde transport. Through experiments aimed at identifying CD11b/CD18-binding proteins, we produced a monoclonal antibody termed E1B2 that recognizes a 28-kDa membrane protein that co-precipitates with CD11b/CD18. Microsequence analysis of the E1B2 antigen revealed that it is BAP31. Co-association of CD11b/CD18 and BAP31 was confirmed in co-immunoprecipitation and protein binding assays. Additional experiments revealed that the binding of BAP31 to CD11b/CD18 was not dependent on divalent cations nor mediated by the I-domain of CD11b. Using glutathione S-transferase fusion chimeras, we determined that binding of CD11b/CD18 to BAP31 is mediated through interactions with the cytoplasmic tail of BAP31. Immunolocalization studies revealed colocalization of BAP31 and CD11b/CD18 within neutrophil secondary granules. Subcellular fractionation studies in polymorphonuclear leukocytes (PMN) revealed similar patterns of redistribution of BAP31 and CD11b/CD18 from fractions enriched in secondary granules to the plasma membrane following stimulation with formylmethionylleucylphenylalanine (fMLP). Given the known sorting properties of BAP31, these findings suggest that BAP31 may play a role in regulating intracellular trafficking of CD11b/CD18 in neutrophils.

Enhanced activation of and increased production of matrix metalloproteinase-9 by human blood monocytes upon adhering to carbamylated collagen

Carbamylation refers to chemical modification of protein side chains by cyanate derived e.g. from urea. It alters their structural and functional properties. We have studied the influence of the carbamylation of type I collagen in vitro on its interactions with elutriated human monocytes, and its potential role in atherosclerosis. Adhesion of monocytes onto carbamylated collagen was significantly enhanced compared to native collagen. There was no change in superoxide anion production. On the other hand, there was an increase in the production and the activation of matrix metalloproteinase-9. No effect was found on tissue inhibitor of metalloproteinase-1 production. Thus, the presence of carbamylated collagen may stimulate the remodelling of extracellular matrix mediated by activated monocytes. Such alterations may contribute to enhanced atherosclerosis in renal insufficiency, a pathological condition associated with elevated levels of carbamylation.

Enhancement by neutrophils of collagen degradation by corneal fibroblasts

Activated corneal fibroblasts and infiltrated leukocytes are thought to contribute to corneal ulceration. The potential roles of neutrophil-fibroblast and cell-matrix interactions in the degradation of stromal collagen associated with corneal ulceration have now been investigated with the use of three-dimensional cultures of rabbit cells in collagen gels. Degradation of collagen fibrils during culture was measured by spectrophotometric determination of released hydroxyproline. Whereas corneal fibroblasts alone degraded collagen fibrils to a small extent, neutrophils did not. However, the addition of neutrophils or neutrophil-conditioned medium (CM) to cultures of corneal fibroblasts resulted in a marked increase in the amount of collagen degraded by the fibroblasts. The effect of CM from neutrophils cultured in collagen gels on collagen degradation by corneal fibroblasts was greater than that of medium conditioned by neutrophils in monolayer culture. Immunoblot as well as reverse transcription and real-time polymerase chain reaction analyses revealed that neutrophil-CM stimulated the synthesis of matrix metalloproteinase (MMP)-1 and MMP-3 by corneal fibroblasts. The stimulatory effect of neutrophils on collagen degradation by corneal fibroblasts was inhibited by the synthetic MMP inhibitor ilomastat and by interleukin-1 (IL-1) receptor antagonist. These results suggest that factors secreted by collagen-stimulated neutrophils augment collagen degradation by corneal fibroblasts through a stimulatory effect on MMP synthesis and that IL-1 released by neutrophils may contribute to this effect.

Immunotoxicity of epicutaneously applied anticoagulant rodenticide warfarin: evaluation by contact hypersensitivity to DNCB in rats

The immunotoxicity of epicutaneously administered anticoagulant rodenticide warfarin (WF) was examined in this work by using experimental contact hypersensitivity (CHS) reaction to hapten dinitrochlorobenzene (DNCB). WF (0.05 and 0.5 mg/kg) administration 24 h before the induction of CHS does not change expression of CHS evaluated by ear swelling assay. Regional draining lymph node response during sensitization phase was characterized by decreased cellularity but increased spontaneous and IL-2 stimulated proliferation of draining lymph node cells (DLC). No changes in IL-2 production and in numbers of CD25(+) cells were noted and even decreased proliferative index (ratio of IL-2 stimulated to unstimulated DLC proliferation) was detected. Increase in granulocyte activity (MTT reduction and adhesion to plastic) was noted following application of WF solely with further increase following subsequent application of DNCB, when granulocyte activation (NBT reduction) was noted also. Access of WF into general circulation might be responsible for observed changes, what was supported by ex vivo changes in DLC and granulocyte functions assessed before initiation of sensitization and by in vitro effect of exogenous WF as well. Differential effects of WF on lymphocytes and granulocytes noted in this study highlight the need for simultaneous testing of both cell type activity what might constitute a more integrated approach in immunotoxicity studies.

The interplay between integrins alphaMbeta2 and alpha5beta1 during cell migration to fibronectin

A directed migration of leukocytes through the extracellular matrix requires the regulated engagement of integrin cell adhesion receptors. The integrin alpha(M)beta(2) (CD11b/CD18, Mac-1) is progressively upregulated to high levels on migrating phagocytic leukocytes in response to inflammatory stimuli and is able to bind numerous ligands in the interstitial matrix. The role of alpha(M)beta(2) in migration of leukocytes through the extracellular matrix and its cooperation with other leukocyte integrins during migration are not understood. Using a model system consisting of cells that express different levels of alpha(M)beta(2) and an invariable level of endogenous integrin alpha(5)beta(1), we have explored a situation relevant to migrating neutrophils when alpha(M)beta(2) and alpha(5)beta(1) engage the same ligand, fibronectin. We show that fibronectin is a ligand for alpha(M)beta(2) and that both alpha(M)beta(2) and alpha(5)beta(1) on the alpha(M)beta(2)-expressing cells contribute to adhesion to fibronectin. However, migration of these cells to fibronectin is mediated by alpha(5)beta(1), whereas alpha(M)beta(2) retards migration. The decrease in migration correlates directly with the increased alpha(M)beta(2) density. Ligation of alpha(M)beta(2) with function-blocking antibodies can reverse this effect. The restorative effects of antibodies are caused by the removal of restraint imposed by the excess of alpha(M)beta(2)-fibronectin adhesive bonds. These findings indicate that alpha(M)beta(2) can increase general cell adhesiveness which results in braking of cell migration mediated by integrin alpha(5)beta(1). Because alpha(M)beta(2) binds numerous proteins in the extracellular matrix with a specificity overlapping that of the beta(1) integrins, the results suggest that alpha(M)beta(2) can affect the beta(1) integrin-mediated cell migration.

A molecular basis for integrin alphaMbeta 2 ligand binding promiscuity

The leukocyte integrin alpha(M)beta(2) is a highly promiscuous leukocyte receptor capable of binding a multitude of unrelated ligands. To understand the molecular basis for the broad ligand recognition of alpha(M)beta(2), the inter-integrin chimera was created. In the chimeric integrin, the betad-alpha5 loop-alpha5 helix segment comprised of residues Lys(245)-Arg(261) from the alpha(M)I domain of alpha(M)beta(2) was inserted into the framework of alpha(L)beta(2). The construct was expressed in HEK 293 cells, and the ability of generated cells to adhere to fibrinogen and its derivatives was characterized first. Grafting the alpha(M)(Lys(245)-Arg(261)) sequence converted alpha(L)beta(2) into a fibrinogen-binding protein capable of mediating efficient and specific adhesion similar to that of wild-type alpha(M)beta(2). Verifying a switch in the binding specificity of alpha(L)beta(2), the chimeric receptor became competent to support cell migration to fibrinogen. Mutations at positions Phe(246), Asp(254), and Pro(257) within Lys(245)-Arg(261) of alpha(M)beta(2) produced significant decreases in cell adhesion, illustrating the critical role of these residues in ligand binding. The insertion of alpha(M)(Lys(245)-Arg(261)) imparted to the chimeric integrin the ability to recognize many typical alpha(M)beta(2) protein ligands. Furthermore, cells expressing the chimeric receptor, but not alpha(L)beta(2), were able to stick to uncoated plastic, which represents the hallmark of wild-type alpha(M)beta(2). These results suggest that alpha(M)(Lys(245)-Arg(261)) serves as a consensus binding site for interaction with a variety of distinct molecules and, thus, may define the degenerate recognition properties inherent to alpha(M)beta(2).

Degranulation of primary and secondary granules in adherent human neutrophils

The aim of this study was to investigate whether neutrophil adhesion to extracellular matrix proteins like fibronectin, fibrinogen, and albumin influence the release proteins from primary and secondary granules of neutrophils stimulated by phorbol-myristate-acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (f-MLP). Isolated granulocytes plated on wells coated with fibronectin, fibrinogen, and albumin were stimulated with f-MLP (10-7 mol/l), PMA (10-9 mol/l), Mn2+ (5 mmol/l), or combinations of these stimuli, and the degree of adhesion to protein-coated surfaces and the amount of granule proteins released was quantified during 90 min of incubation. PMA, in combination with Mn2+, induced a maximum release of approximately 80% of the intracellular content of lactoferrin and human neutrophil lipocalin (HNL) and 15-20% of the myeloperoxidase (MPO) content regardless of the protein used. PMA or f-MLP alone induced 30-40% release of lactoferrin and HNL depending on the protein that the cells were plated on. Adhesion and release of lactoferrin and HNL were quantitatively related when induced by PMA and PMA plus Mn2+, but not by f-MLP. The mean release of lactoferrin and HNL showed a significant negative relationship to the viability of the cells. In conclusion, adhesion modulates neutrophil degranulation, but it is not always quantitatively related or related in time.

Effects of interleukin 2 therapy on lymphocyte magnesium levels

Interleukin 2 (IL-2) can cause partial or complete tumor regression in approximately 20% of patients with renal cell carcinoma. Among the many physiologic effects of IL-2, decreased serum levels of the divalent cations magnesium (Mg) and calcium have been demonstrated, with corresponding decreases in their urinary excretion. We investigated the effect of IL-2 on lymphocyte Mg levels among patients receiving three different dosing regimens. Twenty-eight patients with metastatic renal cell carcinoma were treated with high-dose intravenous, low-dose intravenous, or subcutaneous IL-2 therapy. Serum ionized Mg, urinary Mg, and peripheral blood mononuclear cell Mg levels were measured in samples from patients during treatment and compared with pretreatment levels. Serum Mg and ionized Mg levels decreased for all patients within 12 hours of treatment (P <.005) and remained low for the duration of therapy. Urinary Mg decreased in parallel with serum levels in all patients (P <.005). The peripheral blood mononuclear cell Mg content per cell increased within 24 hours of treatment (P <.005). The magnitude of these changes was similar during the first week of treatment for patients receiving intravenous or subcutaneous administration of IL-2. During IL-2 therapy, lymphocyte Mg increases coincident with serum Mg depletion. Mg availability may have functional implications for lymphocyte proliferation and integrin function.

Cell adhesion and migration properties of beta 2-integrin negative polymorphonuclear granulocytes on defined extracellular matrix molecules. Relevance for leukocyte extravasation

Regulated adhesion of leukocytes to the extracellular matrix is essential for transmigration of blood vessels and subsequent migration into the stroma of inflamed tissues. Although beta(2)-integrins play an indisputable role in adhesion of polymorphonuclear granulocytes (PMN) to endothelium, we show here that beta(1)- and beta(3)-integrins but not beta(2)-integrin are essential for the adhesion to and migration on extracellular matrix molecules of the endothelial cell basement membrane and subjacent interstitial matrix. Mouse wild type and beta(2)-integrin null PMN and the progranulocytic cell line 32DC13 were employed in in vitro adhesion and migration assays using extracellular matrix molecules expressed at sites of extravasation in vivo, in particular the endothelial cell laminins 8 and 10. Wild type and beta(2)-integrin null PMN showed the same pattern of ECM binding, indicating that beta(2)-integrins do not mediate specific adhesion of PMN to the extracellular matrix molecules tested; binding was observed to the interstitial matrix molecules, fibronectin and vitronectin, via integrins alpha(5)beta(1) and alpha(v)beta(3), respectively; to laminin 10 via alpha(6)beta(1); but not to laminins 1, 2, and 8, collagen type I and IV, perlecan, or tenascin-C. PMN binding to laminins 1, 2, and 8 could not be induced despite surface expression of functionally active integrin alpha(6)beta(1), a major laminin receptor, demonstrating that expression of alpha(6)beta(1) alone is insufficient for ligand binding and suggesting the involvement of accessory factors. Nevertheless, laminins 1, 8, and 10 supported PMN migration, indicating that differential cellular signaling via laminins is independent of the extent of adhesion. The data demonstrate that adhesive and nonadhesive interactions with components of the endothelial cell basement membrane and subjacent interstitium play decisive roles in controlling PMN movement into sites of inflammation and illustrate that beta(2)-integrins are not essential for such interactions.

Peripheral blood granulocyte activity following contact sensitization of rats with dinitrochlorobenzene

Contact hypersensitivity (CHS) reaction is a classic example of a cell-mediated reaction. As the afferent phase of the reaction includes inflammation, CHS is a suitable model for investigating non-specific immunity. Some aspects of granulocyte activity in the afferent phase of experimentally induced CHS to dinitrochlorobenzene (DNCB) in two genetically different rat strains, AO and DA were examined in this study. A shift in the ratio of granulocytes to lymphocytes in favour of granulocytes and an increase in granulocyte survival were noted in DA rats. Granulocytes from both strains demonstrated increased levels of NBT reduction and an increase in their adhesion to plastic. Decreased granulocyte adhesion in the presence of monoclonal antibodies to beta2 integrins (anti-CD11b/c and anti-CD18) points to the contribution of these molecules to granulocyte adhesiveness during the sensitization phase of CHS. Stimulation of adhesion in the presence of anti-CD11a antibody, points to a differential modulation of adhesion molecule activity during the afferent phase of CHS. Changes in functional activity of granulocytes demonstrated in this study might contribute to the development of CHS in rats.

Human blood monocytes interact with type I collagen through alpha x beta 2 integrin (CD11c-CD18, gp150-95)

Human blood monocytes are attracted into connective tissues during early steps of inflammation and wound healing, and locally interact with resident cells and extracellular matrix proteins. We studied the effects of type I collagen on monocyte adhesion and superoxide anion production, using human monocytes elutriated from peripheral blood and type I collagen obtained from rat tail tendon. Both acid-soluble and pepsin-digested type I collagens promoted the adhesion of monocytes, whereas only acid-soluble collagen with intact telopeptides induced the production of superoxide. Adhesion and activation of monocytes on acid-soluble type I collagen depended on the presence of divalent cations. mAbs directed against integrin subunits CD11c and CD18 specifically inhibited adhesion and activation of monocytes on type I collagen. Protein membrane extracts obtained from monocytes were submitted to affinity chromatography on collagen I-Sepharose 4B, and analyzed by Western blotting using specific anti-integrin subunit Abs. In the case of both acid-soluble and pepsin-digested collagens, two bands were revealed with mAbs against CD11c and CD18 integrin subunits. Our results demonstrate that monocytes interact with type I collagen through CD11c-CD18 (alpha x beta 2) integrins, which promote their adhesion and activation. For monocyte activation, specific domains of the type I collagen telopeptides are necessary. Interactions between monocytes and collagen are most likely involved in the cascade of events that characterize the initial phases of inflammation.

Simultaneous analysis of eosinophil and neutrophil adhesion to plasma and tissue fibronectin, fibrinogen, and albumin

A simple and convenient assay for the simultaneous measurement of eosinophil and neutrophil adhesion is described. Incubations were performed in microtitre plates coated with different proteins. Adhesion of eosinophils and neutrophils was determined by the use of specific radioimmunoassays for eosinophil cationic protein (ECP) and myeloperoxidase (MPO). Using this assay, Mn2+ induced a significant increase of the adhesion of eosinophils to plasma fibronectin and fibrinogen in a time-dependent fashion, while a small increase of the adhesion of neutrophils to these two proteins was observed. In contrast, a time-dependent potent increment of the adhesion of both eosinophils and neutrophils to tissue fibronectin and albumin was found. Tissue fibronectin preferentially supported eosinophil adhesion compared with that of neutrophils in the presence of Mn2+. PMA (10(-9) mol/l) induced a significant increase in the adhesion of eosinophils and neutrophils of the same pattern to all four proteins. However, when granulocytes were stimulated by Mn2+ in combination with PMA, eosinophils and neutrophils showed different patterns of response to plasma fibronectin and fibrinogen, respectively, but the same pattern of response to tissue fibronectin. f-MLP stimulated an early increase of the adhesion of neutrophils to fibrinogen, while a weak stimulation of the adhesion of eosinophils to plasma fibronectin and fibrinogen and of neutrophils to plasma fibronectin was observed. Co-stimulation with f-MLP and Mn2+ did not induce any additive effects on granulocyte adhesion. In conclusion, the assay allows rapid quantification of eosinophil and neutrophil adhesion and can be used to directly compare the response of neutrophils and eosinophils. The assay is thus suitable for studies aimed at identifying agents with a selective effect on either of the cells.

Congenital disorders sharing oxidative stress and cancer proneness as phenotypic hallmarks: prospects for joint research in pharmacology

In spite of very distinct genotypic assets, a number of congenital conditions include oxidative stress as a phenotypic hallmark. These disorders include Fanconi's anaemia, ataxia telangiectasia, xeroderma pigmentosum and Bloom's syndrome, as well as two frequent congenital conditions: Down's syndrome and cystic fibrosis. Cancer proneness is a clinical feature shared by these disorders, while other manifestations include early ageing, neurological symptoms or congenital malformations. The onset of oxidative stress has been related to excess formation, or defective detoxification, of reactive oxygen species (ROS). This can arise from either the abnormal expression or inducibility of ROS-detoxifying enzymes, or by defective absorption of nutrient antioxidants. Resulting oxidative injury has been characterized through: (i) DNA, protein or lipid oxidative damage; (ii) excess ROS formation (in vitro and ex vivo); (iii) sensitivity to oxygen-related toxicity; (iv) improvement of cellular defects by either hypoxia or antioxidants; and (v) circumstantial evidence for in vivo oxidative stress (as e.g. clastogenic factors). Investigations conducted so far have been confined to individual disorders. Comparative studies of selected indicators for oxidative stress could provide further insights into the pathogenesis of each individual condition. Such a unified approach may have wide-ranging consequences for studies of ageing and cancer.

The beta 1 integrin, very late activation antigen-4 on human neutrophils can contribute to neutrophil migration through connective tissue fibroblast barriers

Polymorphonuclear leucocyte (PMNL) accumulation in extravascular tissues and inflammatory exudates is dependent on their migration through blood vessel endothelium and then through connective tissue. Previously we utilized a barrier of human synovial and dermal fibroblasts (HSF or HDF) grown on microporous filters, as a model of PMNL migration through connective tissue. Those studies showed that beta 2 (CD18) and the beta 1 integrins, very late activation antigen-5 (VLA-5) and VLA-6, in part mediate this PMNL migration. Here we report that VLA-4, which can also be expressed at low levels on activated PMNL, is also involved in PMNL migration induced by C5a through fibroblast (HSF and HDF) barriers, because monoclonal antibody (mAb) to VLA-4 significantly inhibited (by 20-30%) PMNL migration. Blocking the function of CD18, VLA-5 or VLA-6 was not required for detection of the VLA-4-mediated migration. Combination treatment with mAb to VLA-4 and with mAb to VLA-5 or to VLA-6 further inhibited PMNL migration, irrespective of whether CD11/CD18 mechanisms were blocked with anti-CD18 mAb or not. Treatment of PMNL with a peptide based on the VLA-4-binding domain in the CS-1 fragment of fibronectin, but not a control peptide, inhibited PMNL migration to a comparable extent to treatment with mAb to VLA-4. A low level of VLA-4 was expressed on C5a-activated PMNL, detected by immunofluorescence flow cytometry. These results suggest that VLA-4 can be mobilized by human peripheral blood PMNL and can, in addition to VLA-5, VLA-6 and CD11/CD18 integrins, mediate PMNL migration through connective tissue. This is in marked contrast to PMNL transendothelial migration, where beta 1 integrins appear to play no significant role.

Protection from apoptosis in human neutrophils is determined by the surface of adhesion

Recent work suggests that various neutrophil agonists affect the rate of apoptosis in these cells. On the basis of these observations, we hypothesized that signals triggered in neutrophils via their adhesion receptors might also modify their life span. This hypothesis has been tested using human neutrophils adherent to tissue culture plastic, either untreated or coated with extracellular matrix (ECM) proteins or with monolayers of human umbilical vein endothelial cells. To detect and quantitate apoptotic changes in adherent cells, we developed a microtiter plate assay using a cell-permeable DNA-binding fluorescent dye, Hoechst 33342. Use of this assay demonstrated that 1) the number of apoptotic cells among neutrophils adherent to plastic after 6-20 h of incubation was significantly lower than that among neutrophils adherent to the ECM proteins fibronectin or laminin; 2) adhesion to interleukin-1-activated endothelial cells delayed apoptosis, whereas adhesion to nonactivated endothelium accelerated neutrophil death; and 3) monoclonal antibodies directed against intercellular adhesion molecule 1 or against the common beta 2-chain of the leukocyte integrins abolished the protective effect of interleukin-1-activated endothelial cells on apoptosis of adherent neutrophils. These results suggest that the life span of adherent neutrophils. depends on the activating signals triggered by the surface of adhesion.

Mouse polymorphonuclear granulocyte binding to extracellular matrix molecules involves beta 1 integrins

The mechanism of adhesion of purified mouse polymorphonuclear granulocytes (PMN) to extracellular matrix proteins characteristic of basement membranes and the interstitium has been investigated and compared with the adhesion of a mouse progranulocytic cell line, 32DC13, and a mouse monocytic cell line, WEHI 78/24. All three cell types bound specifically to fibronectin and vitronectin to different degrees under different cellular activation states. 32DC13 bound to fibronectin and vitronectin strongly, and this binding increased upon cellular activation with phorbol 12-myristate-13-acetate (PMA) but not with formyl-Met-Leu-Phe. Only 32DC13 showed significant binding to laminin-1. By contrast, WEHI 78/24 and PMN bound only fibronectin and vitronectin; this binding was weak and was altered only marginally upon activation with PMA. In the case of WEHI 78/24, a slight increase in adhesion both to fibronectin and to vitronectin was observed after cellular activation with PMA, while PMN adhesion to both substrates was slightly reduced. The mechanism of binding to fibronectin and vitronectin was similar in the three cell types. The integrin alpha5 beta1 mediated fibronectin adhesion, demonstrating for the first time the existence of a functionally active beta1 integrin on mouse PMN. Vitronectin binding was mediated by alpha(v) beta3, as demonstrated by the ability of alpha(v)-specific cyclic L-Arg-L-Gly-L-Asp-D-Phe-L-Val (RGDfV) peptide (EMD66203), and anti-beta3 antibody to inhibit cell adhesion. 32DC13 adhesion to laminin-1 was via the alpha6 beta1 integrin. None of the three cell types tested bound to the basement membrane proteins collagen type IV and perlecan, or to the interstitial stromal constituents tenascin, collagen types I, V and VI. Interestingly, perlecan and collagen type IV were found to repel all three cell types. The relative inability of PMN, WEHI 78/24, and 32DC13 to bind to extracellular matrix proteins characteristic of basement membranes and their ability to bind inflammatory markers of the interstitium is discussed with respect to leukocyte extravasation processes.

Neutrophil activation by adhesion: mechanisms and pathophysiological implications

Neutrophil adhesion plays an essential role in the formation of an inflammatory exudate. Moreover, adhesion activates selective neutrophil functions and regulates the cell response to additional stimuli. In this review we summarize the information available on adhesion molecules involved in neutrophil adhesion to endothelial cells and extracellular matrix proteins and the experimental approaches which have been developed to block neutrophil adhesion and neutrophil mediated tissue damage. We also address the mechanisms of activation of selective neutrophil functions by adhesion molecules and, in particular the mechanisms of signal transduction by neutrophil integrins. On the basis of recent results obtained in our and other laboratories we propose a model hypothesizing mechanisms of signaling by neutrophil integrins involved in regulation of selective functions.

Mac-1 (CD11b/CD18) is the predominant beta 2 (CD18) integrin mediating human neutrophil migration through synovial and dermal fibroblast barriers

Recently we reported that polymorphonuclear leucocyte (PMNL) migration in vitro through a barrier of human synovial fibroblasts (HSF) involves both beta 2 (CD18) and beta 1 (CD29) integrins on the PMNL. Here we investigated the role of the beta 2 integrin family members, lymphocyte function-associated (LFA)-1 (alpha L beta 2 or CD11a/CD18) and Mac-1 ( alpha M beta 2 or CD11b/CD18), in PMNL migration through HSF and human dermal fibroblast (HDF) monolayers. Treatment of PMNL with monoclonal antibody (mAb) to LFA-1 (anti-alpha L) did not inhibit PMNL migration through either monolayer in response to C5a. In contrast, mAb to Mac-1 (Cd11b) inhibited (by 30-40%) PMNL migration, and by virtually the same extent as mAb to the beta 1 integrin chain (CD18) (40% inhibition). Addition of mAb to LFA-1 to mAb to Mac-1 did not result in greater inhibition. This was in contrast to PMNL migration through human umbilical vein endothelium (HUVE) monolayers, where mAb to LFA-1 or to Mac-1 each partially inhibited PMNL transendothelial migration, and when these mAbs were combined, synergistic inhibition of migration was observed, reaching 90-95% inhibition. Intercellular adhesion molecule 1 (ICAM-1) was not required for Mac-1 mediated migration through HSF or HDF, because treatment of the fibroblasts with mAb R6.5 (F(ab)2) to ICAM-1, which blocks the Mac-1 binding site on ICAM-1, did not inhibit PMNL migration. An LFA-1-ICAM-1 mechanism of PMNL migration through HSF and HDF monolayers could be detected after treatment (4 hr) of the monolayers with TNF-alpha plus IFN-gamma, which upregulated ICAM-1 on the fibroblasts. The results demonstrate the beta 2 integrin dependent PMNL migration in connective tissue may involve primarily Mac-1, with little involvement of LFA-1 or ICAM-1, a situation in marked contrast to PMNL migration across endothelium. However, in inflammatory conditions in which TNF-alpha and/or IFN-gamma may be generated, a role for LFA-1-ICAM-1 may be induced.

The binding of type I collagen to lymphocyte function-associated antigen (LFA) 1 integrin triggers the respiratory burst of human polymorphonuclear neutrophils. Role of calcium signaling and tyrosine phosphorylation of LFA 1

Monoclonal antibodies to the alpha L beta 2 integrin inhibit the binding of type I collagen to PMN (polymorphonuclear neutrophil leukocytes) as well as the subsequent stimulation of superoxide production and enzyme secretion-elicited by this collagen. Pepsinized collagen still binds PMN but no longer stimulates them. The I domain of the alpha chain of the integrin is involved in the binding. Two sequences of the alpha 1(I) polypeptide chain of collagen participate in the process. Experiments of competitive inhibition by synthetic peptides showed that the sequence RGD (915-917) is used for binding to the cells and DGGRYY (1034-1039) serves to stimulate PMN. Experiments of radioactive labeling of the cells and affinity chromatography on Sepharose-collagen confirmed the presence in PMN extracts of two proteins, 95 and 185 kDa, respectively, corresponding to the molecular weights of the beta 2 and alpha L chains of the integrin and recognized by their specific monoclonal antibodies. The transduction pathways depending on the alpha L beta 2 integrin do not involve a G protein (ruled out by the use of cholera and pertussis toxins), whereas the cytoskeleton was found to participate in the process, as evidenced by inhibition by cytochalasin B. After collagen stimulation, cytoplasmic inositol trisphosphate and calcium ion increased sharply for less than 2 min. The use of the inhibitors staurosporine and calphostin C demonstrated that protein kinase C was involved. Evaluation of the activity of this enzyme showed that, upon stimulation of PMN with collagen I, it was translocated to plasma membrane. Acrylamide gel electrophoresis of the protein bands corresponding to the integrin alpha L beta 2, followed by immunoblotting using monoclonal antibodies to phosphotyrosine, permitted us to demonstrate that, prior to stimulation by type I collagen, there was no phosphorylation, whereas after stimulation, both alpha L and beta 2 chains were stained by anti-phosphotyrosine antibodies. The adhesion of PMN to pepsinized type I collagen triggered tyrosine phosphorylation of the beta 2 chain of the integrin, without stimulating O2-. production by these cells, whereas their stimulation by complete type I collagen induced the tyrosine phosphorylation of both alpha L and beta 2 subunits. The tyrosine phosphorylation of both integrin subunits during transduction of stimuli is a heretofore undescribed phenomenon that may correspond to a new system of transmembrane communication.

Nitric oxide reduces hydrogen peroxide production from human polymorphonuclear neutrophils

Nitric oxide has been reported to affect both adhesion and respiratory burst of neutrophils. This indicates a possible role of nitric oxide in regulation of acute inflammatory responses. Release of oxygen metabolites from neutrophils can be measured using luminol-enhanced chemiluminescence and this method can detect both extracellularly and intracellularly released oxygen metabolites. Neutrophils treated with nitroprusside and activated with FMLP, type I collagen or PMA decreased their extracellular release of oxygen metabolites, while their intracellular release was almost unaffected. The effect of nitroprusside was mediated by nitric oxide since treatment with cyanide had the opposite effect. N-ethylmalemide treatment decreased both extra- and intracellular release of oxygen metabolites. This indicates that nitric oxide affects membrane-bound NADPH-oxidase either indirectly or directly, and not a cytosol factor of the oxidase as earlier shown for N-ethylmaleimide. In conclusion, extracellular nitric oxide attenuates extracellularly released oxygen metabolites from activated neutrophils in an inflammatory response.

Priming of oxidative response in human neutrophils by anti-CD18 monoclonal antibodies

Type I collagen, the most abundant protein in the body, after acid extraction adheres to and can induce a respiratory burst from neutrophils. It has been proposed that the effects of collagen are mediated via the CD18 subfamily of integrins. In the present study, adhesion was measured by affinity chromatography in a column containing collagen-coated microcarriers, while oxygen metabolite production was measured with luminol-dependent chemiluminescence. Neutrophil adherence to collagen was attenuated by anti-CD18 monoclonal antibodies. The respiratory burst in response to collagen was not affected by the antibodies. Incubation of neutrophils with anti-CD18 antibodies prior to stimulation with FMLP increased both the extra- and intracellular respiratory burst. Treatment with antibodies prior to PMA stimulation increased only the extracellular respiratory burst. In conclusion, the respiratory burst from neutrophils is primed by pretreatment with anti-CD18 monoclonal antibodies. The collagen-stimulated respiratory burst is probably also primed, but the effect is hidden by the simultaneous attenuation of adhesion.

Collagen induced MMP-2 activation in human breast cancer

Matrix metalloproteinase-2 (MMP-2), a zymogen requiring proteolytic activation for catalytic activity, has been implicated broadly in the invasion and metastasis of many cancer model systems, including human breast cancer (HBC). MMP-2 has been immunolocalized to carcinomatous human breast, where the degree of activation of MMP-2 correlates well with tumor grade and patient prognosis. Using Matrigel assays, we have stratified HBC cell lines for invasiveness in vitro, and compared this to their potential for metastatic spread in nude mice. HBC cell lines expressing the mesenchymal marker protein vimentin were found to be highly invasive in vitro, and tended to form metastases in nude mice. We have further discovered that culture on collagen-I gels (Vitrogen; Vg) induces MMP-2-activator in highly invasive but not poorly invasive HBC cell lines. As seen for other MMP-2-activator inducing regimens, this induction requires protein synthesis and an intact MMP-2 hemopexin-like domain, appears to be mediated by a cell surface activity, and can be inhibited by metalloproteinase inhibitors. The induction is highly specific to collagen I, and is not seen with thin coatings of collagen I, collagen IV, laminin, or fibronectin, or with 3-dimensional gels of laminin, Matrigel, or gelatin. This review focuses on collagen I and MMP-2, their localization and source in HBC, and their relationship(s) to MMP-2 activation and HBC metastasis. The relevance of collagen I in activation of MMP-2 in vivo is discussed in terms of stromal cell: tumor cell interaction for collagen I deposition, MMP-2 production, and MMP-2-activation. Such cooperativity may exist in vivo for MMP-2 participation in HBC dissemination. A more complete understanding of the regulation of MMP-2-activator by type I collagen may provide new avenues for improved diagnosis and prognosis of human breast cancer.

Adhesive effect of certain cytokines and other perturbants on human neutrophils

Pretreatment of normal human neutrophils with certain cytokines and other mediators caused some of the cells to become adhesive and stick to the plastic (polypropylene) incubation tubes during pretreatment and during the assay for phagocytosis of C3b.IgG-coated microspheres. Often as much as 40% of the cells were adherent to the tubes after the reaction. This sticking of the neutrophils to the plastic tubes was confirmed by increase in cytometer sipping time and by lactic dehydrogenase assay of the suspended cells and of the cells stuck on the sides of the empty incubation tubes. Only those perturbants that caused an up-regulation of C3b receptors (CR1, CD35) and in most cases caused an enhancement of phagocytosis mediated the adhesiveness of the cells. Unless these stuck cells were detached by vigorous flushing with cold buffer containing EDTA, many of the cells were not admitted into the cytometer for determination of the effect of the perturbants on binding and phagocytic capacity of the neutrophils. This observation could have implications regarding the possibility of subpopulations of neutrophils and differences in function of adherent cells versus cells in suspension. In the cases studied there was no appreciable difference between the total binding and phagocytic capacities of the adherent and suspended cells.

VLA-2 is the integrin used as a collagen receptor by leukocytes

Cultured T cells and freshly isolated mononuclear leukocytes are able to bind collagen specifically. These leukocytes express equivalent levels of the integrins VLA-1, VLA-2 and VLA-3 which are collagen-binding receptors on other cells. However, only solubilized VLA-2 is able to bind collagen and only monoclonal antibodies specific for alpha 2 or beta 1 subunits are able to block the binding of intact cells to collagen. This restriction provides another example of the dependence of integrin specificity on the cell type on which it is expressed. It was also speculated that the inserted or I domain on the alpha subunits of VLA-1, VLA-2 and the beta 2 integrin family might have a role in collagen binding on the basis of its sequence homology to other types of collagen binding proteins. However, LFA-1, CR3 and p150,95 showed no collagen binding activity, suggesting that the I domain has another function.

Oxidative damage to collagen

Extracellular matrix molecules, such as collagens, are good targets for oxygen free radicals. Collagen is the only protein susceptible to fragmentation by superoxide anion as demonstrated by the liberation of small 4-hydroxyproline-containing-peptides. It seems likely that hydroxyl radicals in the presence of oxygen cleave collagen into small peptides, and the cleavage seems to be specific to proline or 4-hydroxyproline residues. Hydroxyl radicals in the absence of oxygen or hypochlorous acid do not induce fragmentation of collagen molecules, but they trigger a polymerization of collagen through the formation of new cross-links such as dityrosine or disulfure bridges. Moreover, these cross-links can not explain the totality of high molecular weight components generated under these experimental conditions, and the nature of new cross-links induced by hydroxyl radicals or hypochlorous acid remains unclear.