Endogenous fibronectin of blood polymorphonuclear leukocytes: immunochemical characterization and subcellular localization

Investigation on hyperin-cetyltrimethylammonium bromide-fibronectin system by resonance light-scattering technique

A simple, highly sensitive assay for fibronectin (Fn) was reported using resonance light-scattering (RLS) technique based on the enhanced RLS intensity of hyperin-cetyltrimethylammonium bromide (CTMAB)-Fn system. The interaction system of hyperin-CTMAB-Fn was investigated using spectral methods. Mechanistic investigations show that the main reason of the enhanced RLS intensity of Fn is the formation of three-component complex (hyperin-CTMAB-Fn), in which CTMAB acts as a bridge between hyperin and Fn. The effects of pH, surfactant, concentration of CTMAB and hyperin, incubation time and foreign substances on the enhancement of RLS intensity were studied. Under the optimum conditions, the enhancement of RLS intensity is in proportion to the concentration of Fn in the range of 1.9-248ng/ml. The synthetic samples containing Fn were analyzed and results obtained were satisfied.

A Unique Monoclonal Antibody Against Human Plasma Fibronectin, Which Recognizes an Epitope on the Surface of a Subpopulation of Polymorphonuclear Neutrophils

A new monoclonal antibody (MAb) specific to plasma fibronectin, named MO, which was produced by immunizing a mouse with fragments of fibronectin isolated from human plasma, was found to bind to the surface of a subpopulation of peripheral blood polymorphonuclear neutrophils (PMNs) in the presence of physiological concentration of soluble fibronectin. MAb MO had no reactivity with other blood cells such as lymphocytes, monocytes, or platelets. The percentage of the MAb MO-reactive subpopulation of PMNs from healthy donors varied from 0 to 60%. Ten previously established MAbs against fibronectin tested in this study together with MAb MO had no reactivity with the surface of PMNs at all, when tested simultaneously with MAb MO. These results indicate that MAb MO can be a unique and useful tool for analyzing the structure and function of fibronectin-especially the fibronectin expressed on the surface of PMNs.

Interaction of Human Lactoferrin with Cell Adhesion Molecules through RGD Motif Elucidated by Lactoferrin-binding Epitopes

Lactoferrin (LF) is an iron-binding secretory protein, which is distributed in the secondary granules of polynuclear lymphocytes as well as in the milk produced by female mammals. Although it has multiple functions, for example antimicrobial, immunomodulatory, antiviral, and anti-tumor metastasis activities, the receptors responsible for these activities are not fully understood. In this study, the binding epitopes for human LF were first isolated from a hexameric random peptide library displayed on T7 phage. Interestingly, two of the four isolated peptides had a representative cell adhesion motif, Arg-Gly-Asp (RGD), implying that human LF interacts with proteins with the RGD motif. We found that human LF bound to the RGD-containing human extracellular matrix proteins, fibronectin and vitronectin. Furthermore, human LF inhibited cell adhesion to these matrix proteins in a concentration-dependent manner but not to the RGD-independent cell adhesion molecule like laminin or collagen. These results indicate that a function of human LF is to block the various interactions between the cell surface and adhesion molecules. This may explain the multifunctionality of LF.

An endothelial laminin isoform, laminin 8 (α4β1γ1), is secreted by blood neutrophils, promotes neutrophil migration and extravasation, and protects neutrophils from apoptosis

During extravasation, neutrophils migrate through the perivascular basement membrane (BM), a specialized extracellular matrix rich in laminins. Laminins 8 (LN-8) (α4β1γ1) and 10 (LN-10) (α5β1γ1) are major components of the endothelial BM, but expression, recognition, and use of these laminin isoforms by neutrophils are poorly understood. In the present study, we provide evidence, using a panel of novel monoclonal antibodies against human laminin α4 (LNα4) chain, that neutrophils contain and secrete LN-8, and that this endogenous laminin contributes to chemoattractant-induced, αMβ2-integrin–dependent neutrophil migration through albumin-coated filters. Phorbol ester–stimulated neutrophils adhered to recombinant human (rh) LN-8, rhLN-10, and mouse LN-1 (mLN-1) (α1β1γ1) via αMβ2-integrin, and these laminin isoforms strongly promoted chemoattractant-induced neutrophil migration via the same integrin. However, only rhLN-8 enhanced the spontaneous migration. In addition, recruitment of neutrophils into the peritoneum following an inflammatory stimulus was impaired in LNα4-deficient mice. rhLN-8 also protected isolated neutrophils from spontaneous apoptosis. This study is the first to identify a specific laminin isoform in neutrophils and provides evidence for the role of LN-8 in the adhesion, migration, extravasation, and survival of these cells.

Erythromegakaryocytic cells synthesize laminin-8 (alpha4beta1gamma1)

Blood platelets contain laminin-8 (alpha4beta1gamma1), a recently described laminin isoform, but the origin of platelet laminin is at present unknown. Laminin of platelets could be synthesized by megakaryocytes or, alternatively, endocytosed from plasma or other sources. In the present study, the synthesis and presence of laminin-8 in erythromegakaryocytic HEL and DAMI cells were explored. In HEL cells, transcripts for alpha4, beta1, and gamma1 laminin chains were readily detected by RT-PCR. Immunofluorescence flow cytometry demonstrated reactivity of mAbs to laminin beta1 and gamma1 chains with permeabilized cells. Metabolic labeling of HEL cells using [(35)S]methionine and [(35)S]cysteine followed by immunoprecipitation with monoclonal antibodies to beta1 and gamma1 chains revealed bands of approximately 220 and 200 kDa. In the HEL cell lysate, polypeptides of 220 and 200 kDa were recognized by monoclonal antibodies to laminin beta1 and gamma1 chains, respectively, whereas immunoaffinity-purified rabbit antibodies to laminin alpha4 chain gave inconclusive results. However, following immunoaffinity purification on a laminin beta1 antibody-Sepharose column, a 200-kDa band was readily detected by the antibodies to laminin alpha4 chain. Similar results were obtained with DAMI cells. The size of laminin chains of HEL/DAMI cells was similar, though not identical, to the one of platelets, and the alpha4 chain was noncovalently associated to disulfide-bonded beta1gamma1 heterodimer, as in platelets. We conclude that erythromegakaryocytic cells synthesize laminin-8.

Blood platelets contain and secrete laminin-8 (alpha4beta1gamma1) and adhere to laminin-8 via alpha6beta1 integrin

Laminins, a family of heterotrimeric proteins with cell adhesive/signaling properties, are characteristic components of basement membranes of vasculature and tissues. In the present study, permeabilized platelets were found to react with a monoclonal antibody to laminin gamma1 chain by immunofluorescence. In Western blot analysis of platelet lysates, several monoclonal antibodies to gamma1 and beta1 laminin chains recognized 220- to 230-kDa polypeptides, under reducing conditions, and a structure with much slower electrophoretic mobility under nonreducing conditions. Immunoaffinity purification on a laminin beta1 antibody-Sepharose column yielded polypeptides of 230, 220, 200, and 180 kDa from platelet lysates. In the purified material, mAbs to beta1 and gamma1 reacted with the two larger polypeptides, while affinity-purified rabbit antibodies to laminin alpha4 chain recognized the smallest polypeptide. Identity of the polypeptides was confirmed by microsequencing. One million platelets contained on average 1 ng of laminin (approximately 700 molecules per cell), of which 20-35% was secreted within minutes after stimulation with either thrombin or phorbol ester. Platelets adhered to plastic surfaces coated with the purified platelet laminin, and this process was largely inhibited by antibodies to beta1 and alpha6 integrin chains. We conclude that platelets contain and, following activation, secrete laminin-8 (alpha4beta1gamma1) and that the cells adhere to the protein by using alpha6beta1 integrin.

Cellular responses to FMLP challenging: a mini-review

FMLP (N-formyl-methionyl-leucyl-phenylalanine) and other N-formylpeptides are powerful "activators" of polymorphonuclear and mononuclear phagocytes, but they are also active on other cell types. Present knowledge about formylpeptide receptors and the relevant tools for their imaging and the study of their dynamics are briefly discussed. The main responses elicited by FMLP in granulocytes are cell polarisation, the generation of reactive oxygen species, the production of arachidonic acid metabolites, and the release of lysosomal enzymes. The transduction cascades involved and the agents able to modulate these responses are reviewed. Homologous desensitization and heterologous desensitization of the FMLP-receptor following ligation of other chemokine receptors are also outlined. Finally, the receptor expression and the pharmacological and toxic actions of FMLP upon other tissues and organs, and its actions on the developing embryo, are illustrated.

Increased levels of IL-5 positive peripheral blood eosinophils and lymphocytes in mild asthmatics after allergen inhalation provocation

BACKGROUND

In allergic inflammation eosinophils and TH2-like lymphocytes are supposed to be the major effector cells and considered to contribute as cellular source of the key cytokine interleukin (IL)-5.

OBJECTIVE

The purpose of this study was to enable detection of IL-5 containing leucocytes and to investigate whether the number of these cells in the blood circulation differed between healthy and asthmatics before and after allergen provocation.

METHODS

The distribution of intracellular IL-5 in human peripheral blood eosinophils (PBE) and lymphocytes (PBL) has been investigated using fixation and cell membrane permeabilization with octyl-glucopyranoside, the FOG-method, and flow cytometry. The intracellular staining was performed on leucocytes without any prior purification and in vitro stimulation. The specificity of IL-5 binding to intracellular compartment of both PBE and PBL was confirmed by complete inhibition with human recombinant IL-5.

RESULTS

Preformed intracellular IL-5 was detected in the main population of PBE (> 70%) in both healthy individuals and asymptomatic patients. Moreover, preformed intracellular IL-5 was also detected in 4.8% and 2.4% of PBL from healthy individuals and asymptomatic patients, respectively. There was a correlation between the absolute number of PBE and IL-5 positive PBE. In patients with pollen-related asthma, the number of IL-5 positive PBE and PBL increased significantly 24 h after an allergen inhalation provocation (P < 0.05). In the healthy control group no differences regarding IL-5 positive PBE and PBL were obtained pre- and post-allergen challenge.

CONCLUSIONS

In patients with mild allergic asthma, but not in healthy individuals, allergen provocation induces an increased absolute number of IL-5 positive PBE and PBL. The reason for the relatively high number of IL-5 positive PBL is unclear, but a plausible explanation might be that other lymphocyte subsets besides CD4+ TH2 can produce IL-5. However, enumeration of IL-5 positive leucocytes may be used as an activity marker and also be a useful tool in monitoring the inflammation in asthma.

Endogenous fibronectin of blood polymorphonuclear leukocytes: stimulus-induced secretion and proteolysis by cell surface-bound elastase

In an accompanying study, we described the presence of intact fibronectin, a large adhesive molecule, in the specific granules of blood PMNs. Secretion of fibronectin by blood PMNs is poorly understood, and the fate of this fibronectin is practically unknown. In the present study we demonstrate that nanomolar concentrations of phorbol ester or the chemoattractants fMLP, PAF, and LTB4 induce fibronectin secretion from blood PMNs. Phorbol ester induced secretion of approximately 85% of the total fibronectin content, as well as expression of small amounts on the cell surface of the activated PMNs. Secreted fibronectin was proteolytically cleaved and, after 20 min, four major fragments of 150, 120, 90, and 80 kDa containing a midchain epitope were identified by Western blot analysis. Kinetic studies indicated that fibronectin was rapidly secreted as an intact molecule and that proteolysis started within minutes and proceeded for at least 1 h. If cells were removed after 5 min TPA treatment, no further proteolysis of the secreted fibronectin was observed, indicating participation of cell-bound proteinases. From a cocktail of proteinase inhibitors, PMSF was the most active in suppressing fibronectin proteolysis. Studies with specific peptidyl inhibitors of human leukocyte elastase and cathepsin G, major serine proteinases of PMNs, demonstrated some inhibition with the cathepsin G inhibitor, while the human leukocyte elastase inhibitor almost completely abolished fibronectin proteolysis. A monoclonal antibody to the elastase had a similar effect. The results indicate that intact fibronectin is a secretory product of blood PMNs and that this endogenous adhesive molecule is within minutes extracellularly processed by cell surface-bound elastase.