Impact of glycoprotein VI and platelet adhesion on atherosclerosis--a possible role of fibronectin

Glycoprotein VI (GPVI) mediates binding of platelets to subendothelial collagen during acute arterial thrombosis. GPVI interactions with the activated atherosclerotic vascular endothelium during early atherosclerosis, however, are not well understood. In ApoE-/- mice, platelet adhesion to atherosclerotic arteries was increased, as measured by intravital microscopy. This platelet adhesion was significantly inhibited by IV injection of GPVI-Fc (1 mg/kg body weight). Atherosclerosis in ApoE-/- mice was attenuated both after 7 and 10 weeks of treatment with the anti-GPVI antibody JAQ1 (2 mg/kg body weight i.p. twice weekly). Binding of GPVI-Fc (1 mg/kg IV) occurred to deeper layers, but also to the luminal site of plaques in atherosclerotic rabbits, but not to the vessel wall of healthy littermates. Gene transfer of GPVI-Fc to the carotid vascular wall significantly attenuated athero-progression and endothelial dysfunction in atherosclerotic rabbits in vivo. Specific binding of the soluble GPVI receptor (GPVI-Fc) to fibronectin was found in vitro to coated ELISA plates. Platelet adhesion to fibronectin was significantly inhibited both by GPVI-Fc and by the anti-GPVI antibody 5C4 ex vivo in flow chamber experiments. GPVI plays a role in platelet adhesion to atherosclerotic endothelium in the absence of plaque rupture. Inhibition of GPVI both via GPVI-Fc and anti-GPVI-antibodies results in protection against atherosclerosis in both cholesterol-fed rabbits and ApoE-/- mice. This novel mechanism of GPVI-mediated platelet adhesion-possibly via fibronectin-could relevantly contribute to platelet-triggered atheroprogression.

Platelets in regeneration

Platelets, as the first cellular response after disruption of vascular and/or tissue integrity, cover any existing injury within our body. But is the regenerative potential of platelets limited to providing a cellular patch for wounds? This review highlights the recent advance in our understanding of platelets being distinctly regulated and regulating cells that contribute immensely to the healing process from the very initial stage to the late events of tissue regeneration. For instance, the intrinsic actions of platelets as a regenerative cell, the participation of platelets in angiogenic processes, and the interplay of platelets and circulating stem and progenitor cells, as well as potential therapeutic implications, are addressed. Although we are starting to understand the underlying mechanisms connecting platelets to the components of tissue regeneration just mentioned, many aspects remain to be elucidated. The demand to invest research in this area is underscored by the fact that platelets or platelet-derived molecules are already applied in clinical contexts such as connective tissue regeneration, whereas other research fields have largely neglected platelet effects going beyond their participation in the coagulation cascade. Understanding the mechanisms connecting platelets to tissue regeneration, however, will inevitably open novel options in regenerative medicine.

Increased circulating progenitor cells in Alzheimer's disease patients with moderate to severe dementia: evidence for vascular repair and tissue regeneration?

Cerebrovascular dysfunction is a common finding in patients with Alzheimer's disease (AD) and may contribute to cognitive decline. Abundant evidence suggests that vascular and neuronal repair mechanisms are mediated by circulating progenitor cells in vivo. Whether CD34+ and, specifically, CD34+/CD133+ progenitor cells are involved in the pathophysiology of AD is poorly understood so far. In the present study, peripheral blood concentrations of circulating CD34+/CD133+ and CD34+ progenitor cells were measured in 45 AD patients and in 30 healthy elderly controls by flow cytometry. The severity of dementia was assessed by Mini-Mental Status Examination and Clinical Dementia Rating scale. AD patients were stratified into two groups showing mild (n=17) and moderate to severe (n= 28) dementia. In the present study, AD patients with moderate to severe dementia, but not those with mild dementia, showed significantly increased circulating CD34+/CD133+ and CD34+ progenitor cells compared to healthy elderly controls independent of cardiovascular risk factors and medication. In addition, the number of circulating CD34+/CD133+ progenitor cells in AD patients was significantly inversely correlated with cognitive function, age, and plasma levels of SDF-1, the most potent chemokine for progenitor cells. Our findings suggest a stage-dependent upregulation of circulating CD34+/CD133+ and CD34+ progenitor cells in AD patients, which could take part in tissue healing processes of the brain in AD.

Platelet glycoprotein VI (GPVI) for early identification of acute coronary syndrome in patients with chest pain

BACKGROUND

Platelet glycoprotein VI (GPVI) is elevated in patients with acute coronary syndrome (ACS), stroke and associated with acute coronary events. GPVI may be helpful to distinguish an imminent ACS from non-coronary (NC) causes in patients with chest pain who were transferred to chest pain unit, before the myocardial necrosis is evident with classical biomarkers.

METHODS

Based on the findings of our previous studies, we consecutively examined 1004 patients with chest pain in a prospective study design. ACS was found in 416 (41.4%), stable angina pectoris (SAP) in 233 (23.2%), and NC causes of chest pain (hypertension, musculoskeletal disease, pulmonary embolism, myocarditis, cardiophobia) in 355 patients (35.4%). Platelet surface expression of GPVI was measured by flow cytometry.

RESULTS

Patients with ACS showed significantly enhanced GPVI expression levels compared to patients with SAP or NC causes of chest pain (ACSvs.SAP(mean fluorescence intensity (MFI)+/-SD):18.9+/-7.4vs.17.9+/-9.5;P=0.028;ACSvs.NC:15.4+/-6.9;P=0.002). Elevated GPVI expression was associated with ACS independent of markers of myocardial necrosis like troponin and creatine kinase-MB. Patients with an elevated GPVI expression (MFI>or=18.6) had a poorer clinical outcome than patients with baseline GPVI expression in regard to composite cumulative survival that included myocardial infarction, stroke, and cardiovascular death at three months (Log rank;P=0.025).

DISCUSSION

Platelet GPVI surface expression is enhanced in patients at risk for an ACS and is an early marker for imminent acute coronary events in patients with chest pain.

EMMPRIN (CD147) is a novel receptor for platelet GPVI and mediates platelet rolling via GPVI-EMMPRIN interaction

The Extracellular Matrix Metalloproteinase Inducer (EMMPRIN, CD147, basigin) is an immunoglobulin-like receptor expressed in various cell types. During cellular interactions homotypic EMMPRIN-EMMPRIN interactions are known to induce the synthesis of matrix metalloproteinases. Recently, we have identified EMMPRIN as a novel receptor on platelets. To our knowledge EMMPRIN has not been shown to serve as adhesion receptor, yet. Here we characterise platelet glycoprotein VI (GPVI) as a novel adhesion receptor for EMMPRIN. Human platelets were prestimulated with ADP and perfused over immobilised recombinant EMMPRIN-Fc or Fc-fragments under arterial shear conditions. ADP-stimulated platelets showed significantly enhanced rolling (but not enhanced firm adhesion) on immobilised EMMPRIN-Fc compared to Fc. Pretreatment of platelets with blocking mAbs anti-EMMPRIN or anti-GPVI leads to a significant reduction of rolling platelets on immobilised EMMPRIN-Fc, whereas pretreatment with blocking mAbs anti-p-selectin, anti-alpha4-integrin or anti-GPIIb/IIIa complex (20 microg/ml each) had no effect. Consistently, chinese hamster ovary (CHO) cells stably transfected with GPVI showed enhanced rolling (but not adhesion) on immobilised EMMPRIN-Fc in comparison to non-transfected CHO cells. Similarly, CHO cells stably transfected with EMMPRIN showed enhanced rolling on immobilised GPVI-Fc (or EMMPRIN-Fc) compared to non transfected CHO-cells. Finally, specific binding of EMMPRIN to GPVI was demonstrated by a modified ELISA and surface plasmon resonance technology with a dissociation constant of 88 nM. Platelet GPVI is a novel receptor for EMMPRIN and can mediate platelet rolling via GPVI-EMMPRIN interaction.

Decreased plasma levels of granulocyte-colony stimulating factor (G-CSF) in patients with early Alzheimer's disease

Alzheimer's disease (AD) is characterized by massive neuronal cell loss in the brain. Granulocyte-colony stimulating factor (G-CSF) is a hematopoietic growth factor that promotes neuroprotective effects and supports neurogenesis in the brain. In the present study, we found significantly lower G-CSF plasma levels in 50 early AD patients in comparison with 50 age-matched healthy controls. In AD patients, G-CSF levels showed a significant inverse correlation with amyloid-beta (Abeta1-42) levels in cerebrospinal fluid, but not with levels of tau protein in cerebrospinal fluid or Mini-Mental Status Examination scores. In addition, G-CSF plasma levels were significantly inversely correlated with age in AD patients and healthy controls. In conclusion, decreased G-CSF plasma levels in early AD patients may contribute to a deficient hematopoietic brain support with putative pathogenic relevance. Further studies are needed to examine whether a modulation of hematopoietic growth factors such as G-CSF could be a promising new therapeutic strategy for AD.

Type I collagen biomarkers in the diagnosis of bone metastases in breast cancer, lung cancer, urinary bladder cancer and prostate cancer. Comparison to CEA, CA 15-3, PSA and bone scintigraphy

PURPOSE

In this study we evaluated the clinical usefulness of serum pro-I collagen peptide (PICP) and I collagen telopeptide (ICTP) as indicators of early bone metastases in patients with breast (BC), lung (LC), urinary bladder (UBC) and prostate cancer (PC).

PATIENTS AND METHODS

305 patients were examined. 145 had histologically confirmed BC (92 with bone metastases), 20 UBC (6 with bone metastases), 11 LC (3 with bone metastases) and 129 PC (68 with bone metastases). In BC patients we compared the PICP and ICTP levels with those of CA 15-3, CEA and bone scintigraphy. Patients with LC and UBC had PICP and ICTP measurements, PC patients had serum PICP, prostate specific antigen (PSA) measurements and bone scans. 104 healthy individuals served as controls.

RESULTS

ICTP and CA 15-3 levels were significantly higher in patients with BC and bone metastases in comparison to patients without metastases (p <0.05), while PICP and CEA were only marginally higher. Significant correlation was observed between existence of bone metastases and ICTP levels (p <0.05). The sensitivity of PICP, ICTP, CEA and CA 15-3 was 28.1, 48.6, 42, and 78%, respectively and specificity was 83.9, 94, 65 and 86%, respectively. ICTP and CA 15-3 were the most reliable markers for early diagnosis of bone metastases in BC. PICP alone or with ICTP were not sensitive enough. Only CA 15-3 showed sensitivity 78% and specificity 86%. When combined CA 15-3, ICTP and CEA the sensitivity and specificity increased to 82% and 96%, respectively. Furthermore, PICP and PSA levels were significantly higher in patients with PC and bone metastases in comparison to patients with benign prostate hyperplasia (BPH) (p <0.0001) or in patients with PC without bone metastases (p <0.0005 for PICP and p <0.0001 for PSA). The co-evaluation of PICP and PSA improved the sensitivity (78%), specificity (96%), accuracy (97%) and positive predictive value (97%). In LC patients, ICTP levels differed significantly between patients with and without bone metastases (p=0.025). In UBC patients, PICP levels differed significantly between patients with and without bone metastases (p=0.017).

CONCLUSION

ICTP and CA 15-3 are the most reliable markers for early diagnosis of bone metastases in BC patients. PICP could be useful for diagnosing early bone metastases of PC and combined with PSA and bone scan can be an additional tool in the follow-up of PC patients. For LC patients, ICTP showed a significant difference in the discrimination of patients with and without bone metastases. In UBC patients, PICP showed a significant difference in the discrimination of patients with and without bone metastases.

Influence of platelet count on the expression of platelet collagen receptor glycoprotein VI (GPVI) in patients with acute coronary syndrome

Platelets play a key role in the development of an acute coronary syndrome (ACS) and contribute to cardiovascular events. Platelet collagen receptor glycoprotein VI (GPVI) contributes significantly to platelet adhesion and thrombus formation in ACS. We consecutively investigated both the platelet count and the platelet surface expression of GPVI in 843 patients with a symptomatic coronary artery disease verified by coronary angiography. Four hundred fourteen patients presented with stable angina pectoris and 429 patients with ACS. Platelet surface expression of GPVI and CD62P was determined by flow cytometry and platelet count with a coulter counter, plasmatic soluble GPVI was measured by ELISA. Platelet GPVI expression in patients with ACS was compared to platelet count. Patients with ACS showed significantly elevated GPVI expression levels in the first and second quartiles of platelet count compared to patients with higher platelet count [mean fluorescence intensity (MFI) +/- standard deviation): 1(st) vs. 4(th): 20.44 +/- 6.1 vs. 18.62 +/- 3.7; p=0.012; 2(nd)vs.3(rd):21.2+/-8.5vs.18.76+/-3.7;P=0.03; 2(nd)vs.4(th): 21.2+/-8.5vs.18.62+/-3.7;P=0.004], which was paralleled in trend for the CD62P expression [MFI: 1(st) vs. 4(th): 11.2 +/- 6.8 vs. 12.3 +/- 9; p=0.057; 2(nd) vs. 3(rd): 16.3 +/- 16 vs.12.7 +/- 5.3; p=0.138; 2(nd) vs. 4(th): 16.3 +/- 16 vs.11 +/- 4.4; p=0.043]. In a subgroup of 48 patients with ACS, determination of soluble GPVI showed similar results [plasma GPVI (ng/ml): 1(st)vs.4(th): 1.6 +/- 0.6 vs. 1.2 +/- 0.4; p=0.046; 1(st) vs. 3(rd): 1.6 +/- 0.6 vs. 1.1 +/- 0.5; p=0.038; 2(nd) vs. 3(rd): 1.9 +/- 0.8 vs. 1.1 +/- 0.5; p=0.04; 2(nd) vs. 4(th): 1.9 +/- 0.8 vs. 1.2 +/- 0.4; p=0.056]. Thus, a lower platelet count comes along with a higher GPVI surface expression and plasma concentration in patients with ACS, which potentially reflects increased activation and enhanced recruitment of platelets to the site of vascular injury.

Platelet derived bFGF mediates vascular integrative mechanisms of mesenchymal stem cells in vitro

Patients with myocardial infarction reveal an altered number of circulating mesenchymal stem cells (MSCs). Recently, it was shown that MSCs are able to regenerate myocardial tissue and to differentiate into endothelial cells. The homing mechanisms of MSCs from the circulation into the target tissue, however, are not understood so far. In this study, we evaluated the impact of platelets on MSC recruitment, proliferation, migration and integration into the endothelium. MSCs expressing alpha(v)beta(3) integrin were recruited to human arterial endothelial cells exposed to isolated platelets or IL-1 beta under high shear conditions. Furthermore, induction of vascular injury in vivo resulted in increased recruitment of injected MSCs as assessed by intravital microscopy and depletion of platelets significantly reduced this adhesion. The interaction of platelets and MSCs was inhibited by pre-incubation with the mAb 7E3 or an RGD protein both blocking beta(3) integrin mediated adhesion. Platelets had a chemotactic effect on MSCs, promoted a migratory MSC phenotype and dose- and activation-dependently enhanced migration of MSCs, a process, which was mediated by basic fibroblast growth factor (bFGF). Similarly, platelet derived bFGF increased proliferation of MSCs. Coincubation of MSCs with platelets facilitated integration into an endothelial monolayer, which was significantly reduced by pre-incubation with a blocking mAb to bFGF. We conclude that platelets may play a critical part in the recruitment of MSCs to the endothelium, influence MSC function and promote integration of MSCs into the endothelium.

Regulation of platelet glycoprotein VI (GPVI) surface expression and of soluble GPVI in patients with atrial fibrillation (AF) and acute coronary syndrome (ACS)

BACKGROUND

The platelet collagen receptor glycoprotein VI (GPVI) mediates platelet adhesion to subendothelial matrix and thrombus formation in acute coronary syndrome (ACS). This study examined patients with both ACS and stable coronary artery disease (CAD), which presented with atrial fibrillation (AF) and sinus rhythm (SR).

METHODS AND RESULTS

We evaluated 992 patients with acute or stable CAD, and determined platelet surface expression of GPVI using flow cytometry. Seventy-eight patients presented with nonvalvular persistent AF. After 1:1 propensity score matching 156 matched cases with 78 pairs were obtained. Patients with AF and ACS showed a significantly decreased GPVI expression compared to patients with ACS and SR, whereas patients with stable angina pectoris (SA) presented with low level activation and no significant difference between SR and AF [mean fluorescence intensity (MFI) for ACS (SR Vs. AF): 20 +/- 6.3 Vs. 17.7 +/- 4.4; P = 0.023; SA (SR Vs. AF): 18.8 +/- 9.4 Vs. 18.1 +/- 6.1; P = 0.649]. In contrast, soluble GPVI was increased in ACS and AF accordingly [plasma GPVI (ng/ml) for ACS (SR Vs. AF): 1.4 +/- 0.8 Vs. 1.9 +/- 1.1; P = 0.038; SA (SR Vs. AF): 0.9 +/- 0.4 Vs. 1.1 +/- 0.5; P = 0.127].

CONCLUSION

Platelet GPVI surface expression is decreased in patients with AF and ACS compared to patients with SR and ACS. Nonvalvular AF is related to indices of chronic platelet activation and might be responsible for a down-regulation of GPVI receptor density on platelets, while soluble GPVI was increased in ACS and AF accordingly.

Decreased plasma and cerebrospinal fluid levels of stem cell factor in patients with early Alzheimer's disease

Alzheimer's disease (AD) is characterized by massive neuronal cell loss in the brain. Stem cell factor (SCF) is a hematopoietic growth factor (HGF) that promotes neuroprotective effects and supports neurogenesis in the brain. In the present study, we found significantly lower SCF plasma levels in 30 early AD patients (908.5 +/- 181.7 pg/ml) in comparison with 30 age-matched healthy controls (1058.3 +/- 221.5 pg/ml; p = 0.006). SCF plasma levels in AD patients showed a significant inverse correlation with dementia severity as measured by ADAS-Cog (r = -0.289; p = 0.037). AD patients showed significantly lower SCF levels in cerebrospinal fluid (CSF) (131.60 +/- 43.03 pg/ml) in comparison with 15 age- and gender-matched patients with other non-inflammatory neurological disease (NIND) (166.03 +/- 42.5 pg/ml; p = 0.017). In addition, we found significant positive correlations between SCF and CXCL12 (also known as SDF-1) plasma levels in healthy controls (r = 0.341; p = 0.008) and between SCF and CXCL12 CSF levels in AD patients (r = 0.487; p < 0.001). In conclusion, decreased SCF plasma and CSF levels in early AD patients may contribute to a deficient hematopoietic brain support with putative pathogenic and clinical relevance. Further studies are needed to examine whether a manipulation of HGFs such as SCF could be a promising new therapeutic strategy for AD.

Association of platelet-derived soluble glycoprotein VI in plasma with Alzheimer's disease

Accumulating evidence from epidemiological, clinical and experimental studies suggests that vascular risk factors and angiopathic mechanisms are involved in the pathogenesis of Alzheimer's disease (AD). Platelets could be the missing link between AD and the vasculature. Soluble glycoprotein VI (sGPVI) and beta-thromboglobulin (beta-TG) plasma and cerebrospinal fluid (CSF) levels as markers of platelet activity were measured in 30 AD patients and 20 age-matched healthy elderly controls by ELISA. The severity of dementia was assessed by mini-mental state examination (MMSE). We found in AD patients significantly decreased sGPVI plasma levels (0.55+/-0.18ng/ml) as compared to healthy controls (0.75+/-0.43ng/ml; p=0.033). In AD patients, sGPVI levels were positively correlated with beta-TG plasma levels (r=0.244, p=0.05) and with cognitive status as measured by MMSE score (r=0.271; p=0.048). In unconcentrated CSF samples, levels of beta-TG and sGPVI were below the detection limit of the assays in AD patients and healthy controls. Our results suggest an association of sGPVI with the pathogenesis of AD. These findings encourage future research into whether sGPVI plasma levels may reflect or even mediate neuroprotective mechanisms in AD.

Platelet collagen receptor glycoprotein VI as a possible novel indicator for the acute coronary syndrome

BACKGROUND

Platelet collagen receptor glycoprotein VI (GPVI) plays a critical role in acute coronary thrombosis. This prospective study examined the predictive value of GPVI for acute coronary syndromes (ACS) in a large consecutive group of patients with symptomatic coronary artery disease to identify the high-risk cohort with imminent coronary events.

METHODS

We evaluated 1,003 patients with symptomatic coronary artery disease, verified by coronary angiography, and determined the surface expression of GPVI using flow cytometry. In a subgroup of 471 patients, who were treated with aspirin plus clopidogrel for coronary stenting, adenosine disphosphate (20 micromol/L)-induced platelet aggregation was evaluated.

RESULTS

Patients with ACS (n = 485) showed a significantly enhanced GPVI expression compared to patients with stable angina pectoris (SAP; n = 518) (mean fluorescence intensity for ACS 19.8 +/- 5.9; SAP 18.7 +/- 8.5, P = .01). Patients with elevated GPVI levels on admission (GPVI cutoff value > or =18.6 mean fluorescence intensity) had a 1.4-fold relative risk for ACS. Logistic regression analysis showed that an elevated platelet GPVI level may indicate ACS independent of biomarkers of myocardial necrosis including troponin, creatine kinase, and creatine kinase-MB. Patients with increased platelet activation (GPVI expression level > or =18.6) showed significant enhanced residual platelet aggregation despite dual antiplatelet therapy compared to patients with low GPVI levels (P = .028).

CONCLUSIONS

Surface expression of GPVI is enhanced in patients with ACS and indicates an imminent acute coronary event before irreversible myocardial necrosis is evident. High GPVI levels are associated with increased residual platelet aggregation despite antiplatelet therapy. Therefore, GPVI is useful to identify the subgroup of patients with a high risk for coronary stent thrombosis and thromboischemic events.

Statins do not adversely affect post-interventional residual platelet aggregation and outcomes in patients undergoing coronary stenting treated by dual antiplatelet therapy

AIMS

There are growing data suggesting a clinical relevance of residual platelet aggregation (RPA) in patients undergoing PCI. Drug-drug interaction of statins and clopidogrel has been controversially discussed in ex vivo studies and clinical trials. The aim of the present study was to investigate the effects of peri-procedural statin medication on the metabolization of aspirin and clopidogrel with regard to platelet aggregation and clinical outcome in patients undergoing coronary intervention.

METHODS AND RESULTS

Patients with coronary stenting for symptomatic coronary artery disease are routinely evaluated by platelet function analysis in a monocentre registry, and for the present study, a consecutive cohort of 1155 patients were analysed. About 87.7% of the patients were treated with statins at the time of platelet function analysis. Residual platelet activity assessed by adenosine diphosphate (20 micromol/L)-induced platelet aggregation was not significantly influenced by statin treatment. Nor the significant effects of CYP3A4-metabolization pathway on post-treatment aggregation were recorded, although there was even a trend to lower RPA values in patients treated with CYP3A4-metabolized statins. Further, in an inter-individual analysis comparing patients treated with CYP3A4- and non-CYP3A4-metabolized statins, no time-dependent difference of clopidogreĺs anti-aggregatory effects was observed. Clinical follow-up of major adverse events (myocardial infarction, ischaemic stroke, death) in 991 patients within 3 months revealed no significant adverse effects of statin treatment on clinical outcome. Instead, statin treatment was independently associated with lower incidence of composite events (HR 0.44, 95% confidence interval 0.23-0.83, P = 0.01).

CONCLUSION

Peri-procedural co-administration of statins does not increase the post-interventional RPA in cardiovascular patients treated with dual antiplatelet therapy and does not worsen the clinical prognosis of these patients.

Platelets modulate atherogenesis and progression of atherosclerotic plaques via interaction with progenitor and dendritic cells

Platelets not only play a role in the late complications of atherosclerosis, but are also essential in its initiation, interacting with endothelial cells and leukocytes. Platelet adhesion to injured or atherosclerotic vessels is critical for the initiation of atherosclerotic lesion formation in vivo. Increasing evidence has recently highlighted the role of progenitor cells in inflammation, atherogenesis, and atheroprogression. Recruitment of progenitor and dendritic cells to sites of vascular injury is poorly understood so far. Both human progenitor and dendritic cells significantly adhere to platelets, indicating that platelets adherent to collagen or to endothelial cells can serve as a bridging mechanism directing circulating progenitor and dendritic cells to sites of impaired vasculature. Moreover, platelets regulate differentiation of progenitor cells to endothelial cells or macrophages and foam cells and modulate essential functions of dendritic cells, including their activation, differentiation and apoptosis in vitro. This review describes recent findings on platelet interaction with progenitor cells or dendritic cells and discusses potential consequences of this interaction in atherosclerosis.

Platelet-Derived Stromal Cell–Derived Factor-1 Regulates Adhesion and Promotes Differentiation of Human CD34 + Cells to Endothelial Progenitor Cells

Background— Peripheral homing of progenitor cells in areas of diseased organs is critical for tissue regeneration. The chemokine stromal cell–derived factor-1 (SDF-1) regulates homing of CD34 + stem cells. We evaluated the role of platelet-derived SDF-1 in adhesion and differentiation of human CD34 + cells into endothelial progenitor cells.

Methods and Results— Adherent platelets express substantial amounts of SDF-1 and recruit CD34 + cells in vitro and in vivo. A monoclonal antibody to SDF-1 or to its counterreceptor, CXCR4, inhibits stem cell adhesion on adherent platelets under high arterial shear in vitro and after carotid ligation in mice, as determined by intravital fluorescence microscopy. Platelets that adhere to human arterial endothelial cells enhance the adhesion of CD34 + cells on endothelium under flow conditions, a process that is inhibited by anti-SDF-1. During intestinal ischemia/reperfusion in mice, anti-SDF-1 and anti-CXCR4, but not isotype control antibodies, abolish the recruitment of CD34 + cells in microcirculation. Moreover, platelet-derived SDF-1 binding to CXCR4 receptor promotes platelet-induced differentiation of CD34 + cells into endothelial progenitor cells, as verified by colony-forming assays in vitro.

Conclusions— These findings imply that platelet-derived SDF-1 regulates adhesion of stem cells in vitro and in vivo and promotes differentiation of CD34 + cells to endothelial progenitor cells. Because tissue regeneration depends on recruitment of progenitor cells to peripheral vasculature and their subsequent differentiation, platelet-derived SDF-1 may contribute to vascular and myocardial regeneration.

Platelet interaction with progenitor cells: potential implications for regenerative medicine

Circulating endothelial progenitor cells have been shown to instigate new vessel formation via angiogenesis and neovascularisation and to induce ongoing vascular and tissue repair by domiciliation to sites of vascular or tissue damage. However, the mechanisms that recruit circulating endothelial progenitor cells towards vascular lesions and regulate repair mechanisms of ischemic peripheral organs are poorly described. Domiciliation of endothelial progenitor cells in peripheral tissue is a multi-step cascade including initial adhesion to subendothelial matrix or endothelium, transmigration and invasion of the target tissue. Platelets are the first circulating blood cells that interact with the injured vessel wall. They contain a number of growth factors, chemokines, cytokines and adhesive proteins that are released or surface-expressed upon platelet activation including adhesion. Recent studies suggest that platelet interaction with endothelial progenitor cells influences chemotaxis, adhesion, activation and differentiation of progenitor cells. Release of the chemokine SDF-1 from platelets enhances neovascularization through mobilization of progenitor cells. Adherent platelets recruit bone marrow-derived progenitor cells to arterial thrombi in vitro and in vivo and induce their subsequent differentiation towards an endothelial phenotype. Moreover, platelet accumulation in a co-culture system with CD34(+) progenitor cells results in the differentiation of the latter to macrophages in vitro. Although further studies are needed to elucidate the mechanisms that platelets determine the fate of endothelial progenitor cells into vascular lesions, platelet interaction with progenitor cells seems to play a decisive role in vascular and tissue regeneration.

Platelet interaction with progenitor cells: vascular regeneration or inquiry?

Increasing evidence supports the role of stem and progenitor cells in vascular regeneration or injury. Following tissue ischemia, progenitor cells are mobilized from their bone marrow or peripheral niches into circulation, adhere at sites of vascular lesion and differentiate into a variety of mature cell types according to their origin and the local environment. Impairment in this pathophysiological process due to either low numbers of circulating progenitor cells or dysfunctional progenitor cells leads to inadequate vascular repair and upon co-existence with different cardiovascular risk factors to vascular injury and atherosclerosis. Vascular repair is a complex process which includes mobilization, chemotaxis, adhesion, proliferation and differentiation of progenitor cells. The common cardiovascular risk factors can impair this process resulting into inhibition of vascular healing and enhancement of inflammatory pathways which ultimately leads to atherosclerosis. Although homing of progenitor cells into bone marrow has been extensively studied, domiciliation of precursor cells into peripheral tissues and differentiation into mature cells are poorly understood so far. Recently, the role of platelets in domiciliation and subsequent differentiation of progenitor cells has been highlighted. Adherent platelets recruit circulating progenitor cells in vitro and in vivo and induce differentiation of the latter into endothelial cells or macrophages and foam cells. Although further studies are needed to describe the mechanisms that lie underneath these observations, it seems that platelet interaction with progenitor cells is an essential step in both vascular regeneration and injury.

The Residual Platelet Aggregation after Deployment of Intracoronary Stent (PREDICT) score

BACKGROUND

Recent studies suggest a high interindividual variability of response to clopidogrel associated with adverse cardiovascular outcome. Different clinical factors are considered to influence a persistent residual platelet aggregation (RPA) despite conventional antiplatelet therapy.

OBJECTIVES

To investigate clinical factors that affect RPA after 600-mg clopidogrel loading in a large unselected cohort of patients with symptomatic CAD.

METHODS

The study population included a consecutive cohort of 1,092 patients treated with coronary stenting for stable angina and acute coronary syndromes (ACS). Residual platelet activity was assessed by ADP (20 micromol L(-1))-induced platelet aggregation >or= 6 h after LD. Eleven clinical factors were included in the primary analysis.

RESULTS

In multivariate regression analysis increased RPA was significantly influenced by ACS, reduced LV-function, diabetes mellitus, renal failure (creatinine > 1.5 mg dL(-1)), and age > 65 years. In a factor-weighed model the risk for high RPA increased with higher score levels (OR for patients with a score of 1-3, 1.21, 95% CI 0.7-2.1; score 4-6, OR 2.0, 95% CI 1.17-3.5; P = 0.01; score 7-9, OR 3.3, 95% CI 1.8-6.0). During a 30-day follow-up the incidence of major adverse events was higher in patients with RPA in the upper tertile (4.8% vs. 2.5% in the 2nd and 1.5% in the 1st tertile; P < 0.05).

CONCLUSIONS

The PREDICT score provides a good tool to estimate residual platelet activity after clopidogrel LD by easily available patient details. Additionally, we demonstrate its association with short-term outcome. Thus, patients with a high score may benefit from intensified antiplatelet therapy by improved platelet inhibition and risk reduction for thromboischemic events.

Association between bone scintigraphy and serum levels of procollagen (I) and PSA in the detection of bone disease in prostate cancer patients

PURPOSE

To evaluate the clinical usefulness of serum procollagen I carboxyterminal propeptide (PICP) and prostate specific antigen (PSA) in relation to bone scan results in Greek patients with prostate cancer (PC).

PATIENTS AND METHODS

108 patients (mean age 58+/-4.3 years; range 42-81) with PC and 52 healthy blood donors as control group were examined for serum PICP and PSA levels. The diagnosis of PC was confirmed histologically. Bone metastases were diagnosed in 68 of the patients with the use of (99m)Tc-MDP bone scan, while 40 patients had no bone metastases. During the one year follow-up new PICP and PSA measurements were obtained along with a new bone scan for all groups studied.

RESULTS

The levels of serum PICP and PSA were significantly higher in patients with PC and bone metastases in comparison to patients with no bone metastases. The sensitivity and specificity of the combination of PICP and PSA were 78% and 96%, respectively.

CONCLUSION

PICP could be useful for diagnosing early bone metastases of prostate adenocarcinoma and in combination with PSA and bone scan can be an additional tool in the follow-up of patients with PC.

Molecular pathways used by platelets to initiate and accelerate atherogenesis

PURPOSE OF REVIEW

The response to injury model in the development of atherosclerosis is broadly accepted by the scientific audience. Platelets are generally not believed to be involved in the initiation of atherosclerosis. New data imply, however, that the response to injury model is too simple for a complete understanding of the inflammatory disease atherosclerosis. The involvement of platelets in the initiation of atherosclerotic lesion formation is critical in directing the atherosclerotic process into regeneration or ongoing vascular injury.

RECENT FINDINGS

Platelets internalize oxidized phospholipids and promote foam cell formation. Platelets also recruit circulating blood cells including progenitor cells to the vessel, that are able to differentiate into foam cells or endothelial cells depending on conditions. Platelets express various scavenger receptors that are able to regulate LDL-uptake. LDL-laden platelets are internalized by adherent progenitor cells that in turn differentiate into macrophages and foam cells.

SUMMARY

An expanding body of evidence continues to build on the role of platelets as initial actors in the development of atherosclerotic lesions. Platelets bind to leukocytes, endothelial cells, and circulating progenitor cells and initiate monocyte transformation into macrophages. Therefore platelets regulate the initiation, development and total extent of atherosclerotic lesions.

Platelet-associated LIGHT (TNFSF14) mediates adhesion of platelets to human vascular endothelium

LIGHT (TNFSF 14) belongs to the tumor necrosis factor super-family and is expressed by different types of immune cells. Recently, LIGHT was found to be associated with platelets and released upon activation. Activation of endothelial cells by recombinant LIGHT results in pro-inflammatory and pro-thrombotic changes, qualitatively comparable to effects of CD40 ligand. Given the important role of platelet-associated CD40 ligand in vascular inflammatory responses we investigated the role of LIGHT for activation of endothelium and adhesion of platelets to endothelial cells. Expression of LIGHT was detected on thrombocytes upon exposure to ADP or TRAP-1. The expression of the LIGHT receptors TR2 and LTbetaR on native human endothelial cells was confirmed by FACS analysis. LIGHT mediated adhesion of platelets to endothelium significantly, occurring both under static and dynamic flow conditions. This interaction was inhibited by a monoclonal antibody to LIGHT but not a control IgG. Moreover, in-vitro stimulation of endothelial cells with recombinant soluble human LIGHT (rhLIGHT) resulted in significantly increased transcriptional and translational upregulation of inflammatory markers ICAM-1, tissue factor (TF) and IL-8. This activation of endothelial cells by LIGHT was mediated by NFkappaB activation and qualitatively comparable to that induced by membrane-bound CD40-ligand on transfected cells. Furthermore, plasma levels of patients with myocardial infarction, in those with ST-elevation myocardial infarction (STEMI), showed increased plasma levels of LIGHT compared with healthy controls. In conclusion, platelet-associated LIGHT is involved in adhesion of platelets to endothelium while soluble LIGHT induces a pro-inflammatory state in vascular endothelial cells. LIGHT may thus be implicated in the pathogenesis of atherosclerosis and acute coronary syndrome, as evidenced by serum levels.

Hyperresponsiveness of platelets in ischemic stroke

Platelet activation and aggregation are critical in the pathogenesis of acute ischemic cerebrovascular diseases. The aim of our study was to characterize platelet function in patients with acute ischemic stroke or transient ischemic attack (TIA), and to evaluate the effect of platelet activation on clinical outcome. One hundred thirty-eight consecutive patients with TIA (n = 74) or stroke (n = 64) were enrolled in this study. Platelet aggregation in response to ADP, epinephrine, arachidonic acid, or collagen, and expression of platelet activation receptors (CD62P, CD63, LIBS-1 and PAC-1) in the acute phase and at three months follow-up were evaluated. Platelets derived from stroke patients were more hyperaggregable in response to agonists in the acute phase compared to TIA patients (p[ADP] = 0.002, p[arachidonic acid] = 0.047, p[epinephrine] = 0.020). Platelet activation was enhanced in the acute phase irrespective of the severity of the disease (stroke or TIA) and returned to baseline levels three months later. Persistent elevated platelet activation at three months follow-up (PAC-1) was associated with increased incidence of recurrent stroke (median, [interquartile range] 3.4, [3.0-5.2] versus 2.9, [2.3-4.0], p = 0.048). In conclusion, platelets are hyperactive in acute stroke compared with TIA. A more intensified dual antiplatelet therapy may be of benefit for stroke patients.

Platelets Recruit Human Dendritic Cells Via Mac-1/JAM-C Interaction and Modulate Dendritic Cell Function In Vitro

OBJECTIVE

Thrombotic events and immunoinflammatory processes take place next to each other during vascular remodeling in atherosclerotic lesions. In this study we investigated the interaction of platelets with dendritic cells (DCs).

METHODS AND RESULTS

The rolling of DCs on platelets was mediated by PSGL-1. Firm adhesion of DCs was mediated through integrin alphaMbeta2 (Mac-1). In vivo, adhesion of DCs to injured carotid arteries in mice was mediated by platelets. Pretreatment with soluble GPVI, which inhibits platelet adhesion to collagen, substantially reduced recruitment of DCs to the injured vessel wall. In addition, preincubation of DCs with sJAM-C significantly reduced their adhesion to platelets. Coincubation of DCs with platelets induced maturation of DCs, as shown by enhanced expression of CD83. In the presence of platelets, DC-induced lymphocyte proliferation was significantly enhanced. Moreover, coincubation of DCs with platelets resulted in platelet phagocytosis by DCs, as verified by different cell phagocytosis assays. Finally, platelet/DC interaction resulted in apoptosis of DCs mediated by a JAM-C-dependent mechanism.

CONCLUSIONS

Recruitment of DCs by platelets, which is mediated via CD11b/CD18 (Mac-1) and platelet JAM-C, leads to DC activation and platelet phagocytosis. This process may be of importance for progression of atherosclerotic lesions.

Platelets and stromal cell-derived factor-1 in progenitor cell recruitment

Stromal cell-derived factor-1 (SDF-1) is a CXC chemokine that binds to its sole counterreceptor, CXCR4. It is well reported that the SDF-1/CXCR4 signaling pathway is of vital importance to human development and to various pathophysiological phenomena, including hematopoiesis, angiogenesis, atherosclerosis, cancer growth, metastasis, and human immunodeficiency virus infection. SDF-1 promotes mobilization of bone marrow-derived endothelial progenitor cells (EPCs) to the circulation in response to vascular injury. Recently, we found that platelets express and release SDF-1 into the microcirculation upon activation and we observed that platelet-derived SDF-1 is functionally involved in recruitment of EPCs to arterial thrombi in vivo. This review discusses the unique functions of this chemokine and the newly discovered impact of platelet-derived SDF-1 into the recruitment of progenitor cells to vascular injury areas, and its subsequent effects in atherosclerosis, vascular repair, and angiogenesis.

EXP3179 Inhibits Collagen-Dependent Platelet Activation via Glycoprotein Receptor-VI Independent of AT 1 -Receptor Antagonism

OBJECTIVE

Thrombus formation after atherosclerotic plaque rupture critically involves the platelet collagen receptor glycoprotein (GP) VI. We investigated the impact of EXP3179, an active metabolite of the angiotensin II type 1 (AT1)-receptor antagonist Losartan (LOS) on GPVI-dependent platelet activation.

METHODS AND RESULTS

EXP3179 and LOS but not EXP3174--the major AT1-receptor blocking metabolite of LOS--dose-dependently inhibited collagen-I (P<0.01) and GPVI-dependent platelet aggregation (P<0.01) analyzed by optical aggregometry. Platelet activation was further determined by flow cytometry measuring the expression of platelet PAC-1, an epitope of the activated fibrinogen-receptor complex. EXP3179 and LOS inhibited collagen-I (P<0.01) and GPVI-dependent PAC-1 expression (P<0.01). EXP3179 and LOS but not EXP3174 decreased the adhesion of GPVI-receptor expressing Chinese hamster ovarian cells on collagen-I under arterial shear conditions determined by flow chamber analysis (P<0.01 and P<0.05). EXP3179 also reduced human atherosclerotic plaque material-induced platelet aggregation (P<0.01) in vitro and murine platelet adhesion after acute vessel injury in vivo as determined by intravital microscopy (P<0.01).

CONCLUSION

EXP3179 acts as a specific inhibitor of the platelet collagen receptor GPVI independent of AT1-receptor antagonism. Further investigations may clarify its individual potential as a novel pharmacological approach to specifically inhibit atherothrombotic events by GPVI-receptor blockade.

The Evil in Atherosclerosis: Adherent Platelets Induce Foam Cell Formation

Platelet interaction with circulating progenitor cells plays an important role for repair mechanisms at sites of vascular lesions. Foam cell formation represents a key process in atherosclerotic plaque formation. We revealed that platelets regulate recruitment and differentiation of CD34 (+) progenitor cells into foam cells and endothelial cells. Adhesion studies showed that platelets recruit CD34 (+) progenitor cells via specific adhesion receptors, including P-selection/P-selectin glycoprotein ligand 1, and beta (1) and beta (2) integrins. CD34 (+) progenitor cells were coincubated with human platelets for 1 week. We demonstrated that a substantial number of CD34 (+) cells differentiated into foam cells. Hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins) and agonists of peroxisome proliferator-activated receptor-alpha and -gamma (PPAR-alpha and -gamma agonists) reduced this foam cell generation via inhibition of matrix metalloproteinase 9 secretions. Foam cell formation is also induced by low-density lipoproteins (LDLs). It was revealed that platelets take up modified LDL (fluorochrome-conjugated acetylated LDL) that is stored in the dense granules and internalized rapidly into the foam cells. These findings emphasize that the balance between endothelial cell regeneration and platelet-mediated foam cell generation derived from CD34 (+) progenitor cells may play a critical role in atherogenesis and atheroprogression.

Platelets induce differentiation of human CD34+ progenitor cells into foam cells and endothelial cells

Recruitment of human CD34+ progenitor cells toward vascular lesions and differentiation into vascular cells has been regarded as a critical initial step in atherosclerosis. Previously we found that adherent platelets represent potential mediators of progenitor cell homing besides their role in thrombus formation. On the other hand, foam cell formation represents a key process in atherosclerotic plaque formation. To investigate whether platelets are involved in progenitor cell recruitment and differentiation into endothelial cells and foam cells, we examined the interactions of platelets and CD34+ progenitor cells. Cocultivation experiments showed that human platelets recruit CD34+ progenitor cells via the specific adhesion receptors P-selectin/PSGL-1 and beta1- and beta2-integrins. Furthermore, platelets were found to induce differentiation of CD34+ progenitor cells into mature foam cells and endothelial cells. Platelet-induced foam cell generation could be prevented partially by HMG coenzyme A reductase inhibitors via reduction of matrix metalloproteinase-9 (MMP-9) secretion. Finally, agonists of peroxisome proliferator-activated receptor-alpha and -gamma attenuated platelet-induced foam cell generation and production of MMP-9. The present study describes a potentially important mechanism of platelet-induced foam cell formation and generation of endothelium in atherogenesis and atheroprogression. The understanding and modulation of these mechanisms may offer new treatment strategies for patients at high risk for atherosclerotic diseases.

Low response to clopidogrel is associated with cardiovascular outcome after coronary stent implantation

AIMS

To assess whether low response to clopidogrel influences cardiovascular outcome after coronary stent implantation in a consecutively measured cohort of patients with coronary stent implantation.

METHODS AND RESULTS

A total of 379 consecutive patients with symptomatic coronary artery disease (CAD), (stable angina n = 206 and acute coronary syndrome, n = 173) treated with percutaneous coronary stenting were enrolled in this trial. Responsiveness to clopidogrel was assessed by ADP (20 micromol/L)-induced aggregometry at least 6 h (mean 34.8+/-25.9 h) after administration of a loading dose of 600 mg clopidogrel. Platelet inhibition < 30% was defined as low response to clopidogrel. At 3-month follow-up, the primary outcome of a combined major cardiovascular event including non-fatal myocardial infarction, non-fatal ischaemic stroke, or cardiovascular death was evaluated. Twenty-two patients (5.8%) were classified as low responders. Compared with patients who adequately responded to clopidogrel, a low responder had a significantly higher risk of major cardiovascular events [22.7 vs. 5.6%; odds ratio, 4.9; 95% confidence interval (CI), 1.66-14.96; P = 0.004]. After adjustment for other factors influencing cardiovascular outcome, low response to clopidogrel and severe left ventricular dysfunction were independently associated with a major cardiovascular event within 3 months (hazard ratio for low response to clopidogrel, 3.71; 95% CI, 1.08-12.69; P = 0.037).

CONCLUSION

Low response to clopidogrel in patients with symptomatic CAD treated by stenting significantly enhances the occurrence of cardiovascular events and death. The evaluation of low response to clopidogrel may help to identify patients at increased risk who may benefit from intensified antiplatelet strategy.

Course of platelet activation and platelet-leukocyte interaction in cerebrovascular ischemia

BACKGROUND AND PURPOSE

Platelet activation plays a crucial role in the pathophysiology of cerebral ischemia. The aim of this study was to investigate the contribution of platelet activation and leukocyte-platelet interactions to the disease.

METHODS

One hundred thirty-five patients with transient ischemic attack (TIA) or stroke were enrolled in this single-center study. They underwent cranial computer tomography within 24 hours of clinical onset and after 3 months, and systemic venous blood samples were drawn. Platelet activation (CD62P expression), leukocyte activation (L-selectin expression), and the appearance of platelet-specific antigens on leukocytes as an index of platelet-leukocyte aggregation were measured by flow cytometric techniques in the acute state and at 3-month follow-up.

RESULTS

Patients with a completed stroke or TIA had significantly increased circulating platelet-leukocyte aggregates, increased P-selectin expression on platelets, and decreased L-selectin expression in the acute state compared with the control group (healthy volunteers). No differences in regard to the tested activation markers could be detected between patients with stroke or TIA in the acute phase of the disease. However, platelet and leukocyte activations were normalized after 3 months in patients with TIA, whereas leukocyte activation (reduced L-selectin expression) remained in stroke patients.

CONCLUSIONS

In patients with TIA and completed stroke, platelet and leukocyte activation is substantially enhanced in the acute phase of the disease. The sustained leukocyte activation observed in stroke but not in TIA patients at 3-month follow up might play a pathophysiological role in the course of the disease.

Human decidual cells can express the Hodgkin's cell-associated antigen Ki-1 (CD30) in spontaneous abortions during the first trimester of gestation

CD30 (Ki-1) antigen has been considered to be expressed on hematopoietic cells including the ones of the recently described anaplastic large cell lymphoma (ALCL), the Reed-Sternberg (RS) cells of Hodgkin's disease and the scattered large parafollicular cells in normal lymphoid tissues. Since then, several reports have been published describing CD30 expression in non-hematopoietic and malignant cells, such as cultivated human macrophages, human decidual cells, histiocytic neoplastic cells, mesothelioma cells, embryonal carcinoma, and seminoma cells. In the present study, we investigated the immunohistochemical expression of CD30 antigen in 15 paraffin-embedded placentas from fetuses after spontaneous abortion in the first trimester of gestation (8th, 10th, and 12th week, respectively) using the monoclonal antibody Ber-H2. All the pregnant patients had been given hormonal medication to support gestation. In addition, a panel of monoclonal antibodies for the identification of leukocytes (CD45/LCA), B-lymphocytes (CD20/L-26), and T-lymphocytes (CD45RO/UCHLI) was performed. Our findings were correlated with those found in 15 placentas obtained from 15 fetuses at the same time, after therapeutic or voluntary abortions. This study demonstrates that, 1) decidual endometrial stromal cells are able to express the CD30 (Ki-1) antigen, 2) the expression of CD30 in decidual cells is higher in cases of hormonal administration (to support gestation), than that found in normal gestation. In the former cases (hormonal support of gestation), a mild mononuclear infiltration of the decidua by UCHLI (T marker) positive cells, accompanies the CD30 positive cells.

K statistic as a measure of quality control in cervicovaginal cytology

Quality assessment schemes are widespread in most branches of pathology but are uncommon in the more subjective areas of histopathology and cytology. Researchers in many fields have become increasingly aware of the observer as an important source of measurement error. The validity of any method of reporting evidence of an abnormal process in cellular material is based on the degree of correlation with the actual disease process as it exists in the tissue and its reproducibility. Correlations can be tested in retrospective studies in which diagnoses based on cellular evidence are matched against the disease process present in biopsy specimens. Correlations can also be tested by examination of a set of unknown cellular preparations obtained in the presence of proven disease. While reproducibility is indirectly related to correlation, it is meant to imply satisfactory utilization of the method by other groups of cytotechnologists and cytopathologists. While cytopathology will continue to play an important role as a screening technique for the detection of cancer of the uterine cervix, its usefulness in the study of the early manifestations of the disease process is yet to be realized on a universal basis.

Expression of laminin, type IV collagen and fibronectin molecules is related to embryonal skin and epidermal appendage morphogenesis

Basement membrane zones are specialized sheets--like arrangements of extracellular matrix proteins and glycosaminoglycans, and act as an interface between parenchymal cells and support tissue. They separate epithelium, endothelium, muscle cells and Schwann cells from adjacent connective tissue stroma, and also from a limiting membrane in the central nervous system. They are involved in several cellular and biological processes, including adhesion, migration and cellular differentiation. Basement membranes have five major components: collagen type IV, laminin, heparan sulfate, entactin, and fibronectin. In addition, there are numerous minor and poorly characterized protein and glycosaminoglycan components. The various components of the basement membranes of the skin (collagen type IV, proteoglycans--heparan sulfate, laminin, entactin and fibronectin) are products of the epithelial (epidermal) cells. We studied immunohistochemically the origin, the first appearance and distribution of the adhesive extracellular glycoprotein laminin and the fibrillar proteins of the extracellular matrix collagen type IV and fibronectin in the basement membranes of fetal human skin between 12 to 21 weeks of gestational age. Additionally, we studied the expression of vimentin in the extracellular matrix of the epithelial/mesenchyme junction of the skin. This study demonstrates clearly that the expression of the antigens laminin, collagen type IV and fibronectin starts in the germinative epithelial cells of the skin at the bulbs of the hair follicles (12th week for fibronectin and 19th week for laminin and collagen type IV), and migrating progressively involves the epithelial epidermal cells of the covering skin, as well as, the basement membrane at the dermal-epidermal junction in that region (between 20 to 21 weeks of gestational age).