Expression and functions of very late antigen 1 in inflammatory joint diseases

Androgens and integrins in salivary glands in Sjogren's syndrome

OBJECTIVE

Laminin alpha1-chain normally induces intercalated duct progenitors to differentiate to acinar cells through integrin (INT) alpha1ss1 and alpha2ss1 receptors. Maintenance of acinar cells is impaired in Sjögren's syndrome (SS), which is also characterized by low levels of serum and salivary androgens. We hypothesized that androgens normally support salivary gland remodeling by upregulating either laminin alpha1 chain or its cellular alpha1 or alpha2 INT subunit-containing receptors.

METHODS

Intercalated duct and acinar human salivary gland (HSG) cells and labial salivary gland (LSG) biopsies from healthy controls and patients with SS were cultured without or with sex steroids. Laminin alpha1 chain and INT alpha1 and alpha2 subunits were studied using quantitative reverse-transcription real-time polymerase chain reaction and INT alpha1 and alpha2 subunits using immunofluorescence staining.

RESULTS

INT alpha1-subunit and alpha2-subunit messenger RNA (mRNA) levels were increased in intercalated duct and acinar cells by DHEA and testosterone. In contrast, laminin alpha1-chain mRNA levels were not affected. The upregulating effect of DHEA on INT subunits was also seen at the protein level. DHEA also increased mRNA levels of both INT subunits in healthy but not SS LSG.

CONCLUSION

Androgens increased INT alpha1 and alpha2 subunits in tubuloepithelial cells and in healthy LSG, but in SS salivary glands this androgen regulation was defective, which is likely to contribute to defective outside-in signaling, acinar atrophy, and ductal cell hyperplasia.

Alpha1beta1 integrin and interleukin-7 receptor up-regulate the expression of RANKL in human T cells and enhance their osteoclastogenic function

Activated T cells, through the production of the receptor activator of NF-kappaB ligand (RANKL) cytokine, have been implicated in the osteoclast development and bone loss that are associated with autoimmune diseases such as rheumatoid arthritis. However, the cellular pathways that regulate the expression of RANKL and the induction of osteoclasts are still unclear. In this study, we show that, in human effector CD4(+) T cells, activation of alpha1beta1 integrin and interleukin (IL)-7 receptor (IL-7R) up-regulates the expression and production of RANKL but has no effect on the production of interferon-gamma, an inhibitor of T-cell-mediated osteoclastogenesis. Thus, both alpha1beta1 integrin and IL-7R enhance the ability of these cells to induce the formation of osteoclasts from human monocytes. Furthermore, we found that simultaneous activation of effector CD4(+) T cells via alpha1beta1 integrin and IL-7R synergistically increases the production of RANKL and enhances their osteoclastogenic function. We also show that, although alpha1beta1 integrin does not protect human effector CD4(+) T cells from IL-2-withdrawal-induced apoptosis, it does enhance the pro-survival effect of IL-7, further emphasizing the importance of the alpha1beta1/IL-7R synergistic effect. Together our results identify a new function of alpha1beta1 integrin in T cells and suggest that activation of effector CD4(+) T cells through alpha1beta1 integrin and IL-7R is an important regulatory pathway in T-cell-dependent osteoclastogenesis. Further understanding of the mechanisms by which IL-7R and alpha1beta1 integrin promote T-cell-mediated osteoclastogenesis will lead to new insights into the regulatory pathways of T-cell-dependent bone resorption associated with autoimmune diseases.

Very late antigen-1 in psoriasis: an immunohistochemical study

BACKGROUND

Currently, psoriasis is thought to be an inflammatory response to an antigenic stimulation, in which angiogenesis plays a fundamental role. Very late antigen-1 (VLA-1) is a beta(1) integrin collagen receptor that is up-regulated in many angiogenic processes. Data on its role in psoriasis are sparse.

OBJECTIVE

In a prospective study, we evaluated the staining of VLA-1 in lesional skin from patients with psoriasis and atopic dermatitis.

MATERIAL AND METHODS

Frozen sections from skin biopsies of patients with chronic plaque-type psoriasis (n = 18) and chronic atopic dermatitis (n = 7) were stained with a monoclonal antibody to VLA-1. The number of blood vessels stained with VLA-1 and the staining intensity were evaluated. These were correlated with the histologic features.

RESULTS

The absolute number of blood vessels was found to be similar in the atopic and psoriatic samples. However, the number of vessels stained with anti-VLA-1, as well as the staining intensity, was shown to be significantly higher in the psoriasis group (P < 0.05). Differences between psoriatic lesions showing typical histological features of psoriasis and those showing features that overlap with dermatitis were found as well.

CONCLUSIONS

Expression of VLA-1 was found significantly higher in lesional dermal blood vessels of psoriatic patients compared with atopic patients. These findings suggest a possible role for VLA-1 in the pathological angiogenesis of psoriasis. It may be an additional tool for establishing the diagnosis of psoriasis and provide a basis for new strategies in the treatment of psoriasis.

The effect of blockade of tumor necrosis factor alpha on VLA-1+ T-cells in rheumatoid arthritis patients

The alpha1beta1 integrin, very late antigen (VLA)-1, characterizes collagen adherent interferon (IFN) gamma producing memory T cells in inflamed synovium. We now report that the mean percentage of VLA-1+ T cells is significantly lower among peripheral blood mononuclear cells of rheumatoid patients responsive to antitumor necrosis factor (TNF) alpha therapy than of those with active disease not receiving therapy. Neutralization of TNFalpha during in vitro polyclonal activation of VLA-1- T cells reduced differentiation to expression of VLA-1 and inhibited secretion of IFNgamma, but did not affect integrin expression on in vivo differentiated VLA-1+ T cells. Moreover, synovial fluids of patients relapsing during and after therapy were enriched in VLA-1+ T cells and lines derived from VLA-1+ T cells in peripheral blood of treated patients retained collagen binding and secreted IFN gamma. Thus, whereas therapy decreases VLA-1+ T cells in rheumatoid arthritis patients, a subset is resistant and contributes to residual and recurring inflammation.

Alpha2 beta1 integrin signaling augments T cell receptor-dependent production of interferon-gamma in human T cells

The mechanisms by which beta1 integrins modulate T cell costimulation are still poorly defined. In this study, we examined the role of collagen-binding integrins alpha1 beta1 and alpha2 beta1 in the regulation of interferon-gamma (IFN-gamma). We demonstrated that ligation of alpha2 beta1 integrin with Collagen type I (Coll I) but not alpha1 beta1 integrin with Collagen IV (Coll IV) significantly augmented T cell receptor (TCR)-dependent expression and production of IFN-gamma by effector T cells. The effect of Coll I was not due to cell adhesion as soluble Coll I also augmented TCR-dependent production of IFN-gamma. Inhibition studies indicated that activation of ERK and JNK MAPKs and PI3K/AKT are necessary for both TCR- and TCR+alpha2 beta1 integrin-dependent IFN-gamma production and that Coll I increases TCR-dependent activation of ERK and JNK MAPKs, and AKT. In addition, our results showed that Coll IV is less potent than Coll I in augmenting TCR-dependent activation of JNK/MAPK, which may explain the differential effect of collagen matrices on TCR-dependent IFN-gamma production. Together, these results indicate that the costimulatory effect of Coll I on IFN-gamma expression is integrated at the levels of ERK and JNK MAPKs and PI3K/AKT signaling pathways and suggest JNK/MAPK as a major signaling pathway of Coll I costimulation. Thus, our study identifies alpha2 beta1 integrin as an important regulatory pathway of IFN-gamma expression and provides novel insights into the signaling mechanisms of integrin costimulation in T cells. As such, this study further supports the functional importance that Coll I interactions may have on the control of T cell-dependent Th1 inflammatory diseases.

α1β1 Integrin+ and Regulatory Foxp3+ T Cells Constitute Two Functionally Distinct Human CD4+ T Cell Subsets Oppositely Modulated by TNFα Blockade

The expression of the collagen receptor alpha(1)beta(1) integrin (VLA-1) on CD4(+) T cells is largely restricted to CCR7(-)CD45RO(+) cells that localize to inflamed tissues. Moreover, neutralizing alpha(1) integrin, in vivo, has been shown to compromise cell-mediated immunity. Our current study shows that the expression of VLA-1 on human CD4(+) T cells is restricted to conventional effectors. In contrast, Foxp3(+) T regulatory cells (Tregs) do not express this receptor. Moreover, Foxp3 or VLA-1 expression remained a mutually exclusive event in CD4(+) T cells even upon polyclonal anti-CD3-induced activation. Because TNFalpha blockade ameliorates certain T cell-dependent autoimmune disorders in humans, we investigated, in vitro, whether neutralizing TNFalpha affected the balance between the proinflammatory VLA-1(+) effectors and the counteracting Tregs. We found that anti-CD3 stimulation of freshly isolated PBL from healthy individuals, coupled with continuous TNFalpha blockade, inhibited the typical activation-dependent generation of CD4(+)VLA-1(+) Th1 cells. In contrast, it augmented the outgrowth of VLA-1(neg/dim)CD25(high) and Foxp3(+)CD4(+) T cells. Indeed, repeated anti-CD3 stimulation coupled with TNFalpha blockade generated CD4(+) T cell lines enriched for VLA-1(-)Foxp3(+) Tregs. Importantly, these CD4(+) T cells displayed potent suppressive functions toward autologous CD4(+) PBL, including the suppression of the activation-dependent induction of VLA-1(+) effectors. Thus, we propose a novel mechanism by which anti-TNFalpha therapy may restore self-tolerance, by shifting the balance between VLA-1(+) effectors and Foxp3(+) Tregs, during immune activation, in favor of the latter suppressor cell population.

The role of very late antigen-1 in immune-mediated inflammation

The alpha1beta1 integrin, also known as "very late antigen" (VLA)-1, is normally expressed on mesenchymal cells, some epithelial cells, activated T cells, and macrophages, and interacts, via the I-domain of the extracellular domain of the alpha1 subunit, with collagen molecules in the extracellular matrix (ECM). By "outside-in" transmembranal signaling to the interior of the cell, it mediates adhesion, migration, proliferation, remodeling of the ECM, and cytokine secretion by endothelial cells, mesangial cells, fibroblasts, and immunocytes. Importantly, its expressions and functions are enhanced by inflammatory cytokines including interferon (IFN)gamma and tumor necrosis factor (TNF)alpha, thus augmenting angiogenesis and fibrosis linked, in particular, to inflammation. Moreover, within the immune system, VLA-1 marks effector memory CD4+ and CD8+ T cells that are retained in extralymphatic tissues by interactions of the integrin with collagen and produce high levels of IFNgamma. Thus, immune-mediated inflammation in vivo is inhibited by blockade of the VLA-1-collagen interaction in experimental animal models of arthritis, colitis, nephritis, and graft versus host disease (GVHD), suggesting that inhibiting the interaction of the alpha1 I-domain with its ligands or modulating "outside-in" signaling by VLA-1 would be a useful approach in the human diseases simulated by these experimental models.

Analysis of cell-free human alpha1 integrin with a monoclonal antibody to the I-domain: detection in ocular fluid and function as an adhesion substrate

The alpha1 beta1 integrin, an inserted (1) domain containing collagen receptor, is expressed in the cell surface membrane of normal and malignant cells, and may play a role in their migration through tissues or in metastatic spread. Here we report that a functional anti-human alpha1beta1 integrin monoclonal antibody (mAb) (1B3.1) directly and specifically binds plastic bound recombinant human alpha1 I-domain protein containing the collagen binding site. Detection was diminished by acidification of the I-domain protein but was enhanced by increasing concentrations of Mg2+ cation. Furthermore, we detected binding of the mAb to proteins from the ocular fluids of 6 patients, with the highest concentration, corresponding to 22.1 ng/ml of I-domain, found in a sample from the eye of a patient with metastatic lung adenocarcinoma. Interestingly, we found that both SKNSH neuroblastoma cells and virally transformed human T cells adhered specifically to plastic wells coated with either immobilized collagen IV or alpha1 I-domain. MAb I B3.1 inhibited adhesion to collagen IV but not to immobilized I-domain. These results suggest a novel function for cell free alpha1 I-domain as a substrate for cellular adhesion, which may have relevance in tumor spread in vivo.

The collagen binding alpha1beta1 integrin VLA-1 regulates CD8 T cell-mediated immune protection against heterologous influenza infection

A common feature of many infections is that many pathogen-specific memory T cells become established in diverse nonlymphoid tissues. A mechanism that promotes the retention and survival of the memory T cells in diverse tissues has not been described. Our studies show that the collagen binding alpha1beta1 integrin, VLA-1, is expressed by the majority of influenza-specific CD8 T cells recovered from nonlymphoid tissues during both the acute and memory phases of the response. Antibody treatment or genetic deficiency of VLA-1 decreased virus-specific CTL in the lung and other nonlymphoid tissues, and increased them in the spleen. In spite of the increase in the spleen, secondary heterosubtypic immunity against flu was compromised. This suggests that VLA-1 is responsible for retaining protective memory CD8 T cells in the lung and other tissues via attachment to the extracellular matrix.

A Monoclonal Antibody to α1β1 Blocks Antigen-induced Airway Responses in Sheep

The integrin alpha1beta1 (very late antigen-1; CD49a/CD29) is a major adhesion receptor for collagen I, IV, and VI, and its induced expression on activated monocytes and lymphocytes plays a central role in their retention and activation at inflammatory sites in autoimmune pathologies. However, the role of alpha1beta1 in allergic settings has not been explored. In this study, we show that a single 45-mg dose of aerosolized monoclonal antibody AQC2 to the alpha1 chain of human and sheep very late antigen-1, given 30 minutes before challenge, blocks both the allergen-induced late response and the associated airway hyperresponsiveness, functional indicators of allergen-induced inflammation, in sheep. AQC2 does not affect the early response. Consistent with these effects, AQC2 tended to reduce the cell response associated with local antigen instillation. An isotype-matched control antibody had no protective effects. Two humanized versions of AQC2, a wild-type IgG1 and an aglycosyl form of the same monoclonal antibody, which has reduced Fc receptor-mediated effector functions, are equally effective in blocking the antigen-induced late response and airway hyperresponsiveness in the sheep model. These data suggest that mononuclear leukocyte adhesion-dependent pathologies contribute to allergic lung disease and provide proof-of-concept that antagonists of alpha1 integrins may be useful in preventing these events.

Expression of the alpha1beta1 integrin, VLA-1, marks a distinct subset of human CD4+ memory T cells

The alpha1beta1 integrin, very late antigen-1 (VLA-1), is a collagen receptor expressed in many CD4+ T cells localizing to inflamed tissues. Here we show that the expression of VLA-1 is a stable marker of a distinct subset of CD4+ memory T cells. Thus, in human peripheral blood lymphocytes (PBLs), approximately 1-4% of the CD4+ T cells express VLA-1, and following T cell receptor activation ex vivo, the percentage of VLA-1+ cells increases within the CD45RO+ population. Importantly, the activated VLA-1+ and VLA-1- cells can be isolated and maintained in culture as phenotypically stable subsets. Functionally, CD4+ memory T cells, operationally defined as the cells that divide rapidly following stimulation with a recall antigen, are highly enriched for VLA-1+ cells. Moreover, depletion of the small fraction of VLA-1+ cells present in CD4+ PBLs prior to stimulation significantly abrogated the proliferative response to recall antigens. Notably, the VLA-1+ cells in fresh CD4+ PBLs are composed of resting CD45RO+/RA-, CCR7-, CD62L+, CD25-, and VLA-4hi cells. Interestingly, this VLA-1+ subset is enriched for Th1-type cells, and Th1-polarizing conditions during T cell activation favor the emergence of VLA-1+ cells. Thus, VLA-1 expression is a stable marker of a unique subset of human memory CD4+ T cells that predominantly differentiates into Th1 cells.

Expression and functional importance of collagen-binding integrins, alpha 1 beta 1 and alpha 2 beta 1, on virus-activated T cells

Adhesive interactions are crucial to cell migration into inflammatory sites. Using murine lymphocytic choriomeningitis virus as an Ag model system, we have investigated expression and function of collagen-binding integrins, alpha(1)beta(1) and alpha(2)beta(1), on activated and memory T cells. Using this system and MHC tetramers to define Ag-specific T cells, we demonstrate that contrary to being VLAs, expression of alpha(1)beta(1) and alpha(2)beta(1) can be rapidly induced on acutely activated T cells, that expression of alpha(1)beta(1) remains elevated on memory T cells, and that expression of alpha(1)beta(1) parallels that of viral-specific effector CD8(+) T cells (defined by tetramer and IFN-gamma staining). In an adoptive transfer model, mAb-mediated blockade of these integrins on activated effector and memory T cells inhibited Ag-specific delayed-type hypersensitivity responses; similar decreased responses were seen upon transfer of alpha(1)-deficient activated/memory T cells. Thus, expression of alpha(1)beta(1) and alpha(2)beta(1) integrins on activated T cells is directly functionally important for generation of inflammatory responses within tissues. Finally, the inhibitory effect of alpha(1)beta(1) blockade on the delayed-type hypersensitivity response could be bypassed by direct injection of Ag-specific T cells to inflammatory sites, demonstrating for the first time in vivo that collagen-binding integrins are involved in leukocyte migration into tissues.

Lovastatin and phospholipase Cgamma regulate constitutive and protein kinase C dependent integrin mediated interactions of human T-cells with collagen

We previously reported that human interleukin (IL)-2 dependent T cell lines derived from very late antigen (VLA)-1(+) CD45RO(+) peripheral blood (PB) T-cells adhere constitutively to collagen type IV, whereas lines from VLA-1(-) PB lymphocytes (L) adhere weakly. Here we report that the latter are induced to adhere by phorbol 12-myristate 13-acetate (PMA). Both PMA dependent and constitutive adhesion, including that of a Herpes Virus Saimiri (HVS) infected CD4(+)VLA-1(+) clone (HVST) were inhibited by anti-VLA-1 monoclonal antibodies (mAb), by inhibitors of phospholipase C (PLC)gamma and by lovastatin but not by a MEK1 inhibitor, whereas only PMA induced adhesion was blocked by inhibition of protein-kinase (PK) C. Furthermore, lovastatin enhanced PLCgamma and anti VLA-1 mAb blockade, and its effect was not reversed by mevalonic acid (MVA). Lovastatin also inhibited interferon (IFN)gamma secretion by T cells triggered with anti-CD3 and in cells detaching from collagen IV. These results suggest new ways for functional modulation of activated T-cells interacting with collagen.

Lymphocytes expressing alpha1beta1 integrin (very late antigen-1) in peripheral blood of patients with arthritis are a subset of CD45RO(+) T-cells primed for rapid adhesion to collagen IV

We report that very late antigen-1 (VLA-1(+)) CD3(+)CD45RO(+) T-cells are selectively segregated from VLA-1(-) peripheral blood (PB) mononuclear cells (MC), in which CD3(+) T-cells are evenly CD45RO(+) and CD45RO(-), when PBMC are stained with a monoclonal antibody (mAb) to VLA-1 and passaged on immunomagnetic columns. In contrast, both VLA-1(+) and VLA-1(-) MC isolated from synovial fluid (SF) are mainly CD45RO(+)CD3(+) T-cells. VLA-1(+) MC formed 13 +/- 5.3% of MC eluting from columns loaded with PBMC of patients with seropositive rheumatoid arthritis (n = 6) and 2.3 +/- 1.6% of patients (n = 4) with other arthritides (P < 0.022). Importantly, only the VLA-1(+) MC from PB and SF adhered to collagen IV upon triggering with phorbol 12-myristate 13-acetate. Moreover, adhesion and migration on collagen IV were preferentially maintained in lines cultured from VLA-1(+) T-cells, and both were inhibited by mAb to the VLA-1 alpha1 I domain. These results suggest that VLA-1(+) CD45RO(+) T-cells in patients with arthritis could play a role in both systemic and local inflammation by rapidly adhering to collagen IV.

Importance of innate immunity and collagen binding integrin alpha1beta1 in TNBS-induced colitis

Inflammation occurs in the context of integrin-mediated adhesive interactions of cells with their extracellular matrix environment. We investigated the role of the collagen binding integrin alpha1beta1 in a model of colitis. alpha1beta1 was expressed on lamina propria T cells and monocytes during disease. Both alpha1 deficiency and anti-alpha1 mAb treatment (prophylactic and therapeutic) protected against colitis. In vivo alpha1beta1 blockade improved macroscopic and histologic scores, decreased inflammatory cytokine production, and profoundly affected the ability of lamina propria mononuclear cells to proliferate and produce IFN-gamma in vitro. Development and alpha1-mediated inhibition of colitis can be lymphocyte independent, suggesting that activated monocytes also represent a key alpha1beta1-expressing cell type involved in colitis. These results underscore the importance of innate immunity and, specifically, of leukocyte/matrix interactions in regulating local inflammatory responses.

Interaction of disease-related antigen-reactive T-cell lines from multiple sclerosis patients with type IV collagen: role of integrin VLA-1 and effects of irradiation

Multiple sclerosis (MS), a chronic demyelinating disease, is thought to be initiated by pathogenic T cells that transmigrate the vascular endothelium and enter the brain through vascular and parenchymal basement membranes (BM). Vaccination with T-cell lines reactive with myelin basic protein (MBP) and myelin oligodendrocytic glycoprotein (MOG) epitopes, expanded with interleukin-2 (IL-2), and attenuated by ionizing radiation is currently being evaluated as a therapeutic modality for this disease. We examined mechanisms potentially involved in pathogenic cell migration into the central nervous system (CNS) and the influence of irradiation on these processes. Seven of 7 autoantigen-responsive T-cell lines from MS patients adhered to collagen IV, the major collagenous constituent of BMs. This adhesion was inhibited almost completely by monoclonal antibody (MAb) to very late antigen (VLA)-1 and partially by anti-VLA-2. T-cell lines from healthy donors adhered more variably to collagen IV. Furthermore, patient derived T cells actively transmigrated through a collagen IV gel toward medium containing TNF-a, in a process that was inhibited by MAbs to VLA-1. Ionizing radiation at the dose used in vaccine preparation, inhibited morphological polarization associated with migratory capability, induced integrin clustering on the cell membrane, and abrogated adhesion to collagen IV. These findings may have important implications for understanding the pathogenesis of MS and how irradiation of potentially pathogenic T cells produces a reagent with possible therapeutic effects in T-cell vaccination (TCV).

Reprogramming T cells: the role of extracellular matrix in coordination of T cell activation and migration

The stable immunological synapse between a T cell and antigen-presenting cell coordinates migration and activation. Three-dimensional collagen gels transform this interaction into a series of transient hit-and-run encounters. Here we integrate these alternative modes of interaction in a model for primary T cell activation and effector function in vivo.

Regulation of inflammation by collagen-binding integrins alpha1beta1 and alpha2beta1 in models of hypersensitivity and arthritis

Adhesive interactions play an important role in inflammation by promoting leukocyte attachment and extravasation from the vasculature into the peripheral tissues. However, the importance of adhesion molecules within the extracellular matrix-rich environment of peripheral tissues, in which cells must migrate and be activated, has not been well explored. We investigated the role of the major collagen-binding integrins, alpha1beta1 and alpha2beta1, in several in vivo models of inflammation. mAb's against murine alpha1 and alpha2 were found to significantly inhibit effector phase inflammatory responses in animal models of delayed-type hypersensitivity (DTH), contact hypersensitivity (CHS), and arthritis. Mice that were alpha1-deficient also showed decreased inflammatory responses in the CHS and arthritis models when compared with wild-type mice. Decreased leukocyte infiltration and edema formation accompanied inhibition of antigen-specific models of inflammation, as nonspecific inflammation induced by croton oil was not inhibited. This study demonstrates the importance in vivo of alpha1beta1 and alpha2beta1, the collagen-binding integrins, in inflammatory diseases. The study also extends the role of integrins in inflammation beyond leukocyte attachment and extravasation at the vascular endothelial interface, revealing the extracellular matrix environment of peripheral tissues as a new point of intervention for adhesion-based therapies.

Anti-very late antigen-1 monoclonal antibody modulates the development of secondary lesion and T-cell response in experimental arthritis

Rats injected in the hind paw with a mixture of Mycobacterium butirricum emulsified in mineral oil (FA) developed a severe polyarthritis that shared some immunological features with human rheumatoid arthritis. After this local administration, rats developed a secondary lesion (edema) in the contralateral paw, which is a hallmark of immune system activation. In vivo intravenous treatment with a monoclonal anti-very late antigen (VLA)-1 antibody (HA31/8) significantly reduced the edema formation in the contralateral paw. T cells isolated from contralateral paw draining lymph nodes of FA rats treated with HA31/8 showed a reduced cell proliferation in vitro, after stimulation with concanavalin A. Furthermore FACS analysis showed that the reduction in proliferation was concomitant to a reduction in the number of T cells positive to surface IL-2 receptor expression. Our data indicate that after in vivo treatment with a monoclonal anti-very late antigen-1 antibody, there is a beneficial effect on the development of the secondary lesion, which correlates to the reduced ability of T cells to proliferate in vitro as well as to a reduced surface expression of IL-2 receptor. The association of this antibody to other drugs interfering at other levels in rheumatoid arthritis may open a new therapeutic window.

Detection of soluble alpha1 integrin in human serum

An enzyme-linked immunosorbent assay (ELISA) for the detection and quantitation of soluble alpha1beta1 integrins (salpha1) in human serum samples was developed. Solid phase-bound anti-alpha1 integrin monoclonal antibody (mAb) TS2/7 was used to capture salpha1, and mAb 1B3.1 was used to detect the immobilized integrin. An extract of human placenta (PE) containing 340 ng/mL of VLA-1 molecules served as a positive control, and serum samples from normal donors and patients were assayed. Optimal binding of anti-alpha1 integrin mAb 1B3.1, expressed as specific optical density (OD), was obtained when a 5 microng/mL solution of anti-alpha1 integrin "capture" mAb TS2/7 was immobilized to the wells and the PE was added. Solutions of albumin or collagen, in contrast, did not result in binding, confirming the specificity of the assay for sal. Furthermore, the specific OD of the wells correlated directly with the concentration of PE. A concentration of salpha1 above that of a 1:100 dilution of PE--that is, >3.4 ng/mL of integrin, in which the intra-assay correlation of variance was <5.7%, was found in 5 of 8, 3 of 8, and 6 of 9 serum samples from normal individuals, patients with connective tissue diseases (CTD), and patients with liver diseases (LD), respectively. These results suggest, for the first time, that salpha1 are present in healthy and diseased human serum.

Tyrosine phosphorylated proteins in synovial cells of rheumatoid arthritis

Two of the key events in the pathogenesis of rheumatoid arthritis are the synovial cell proliferation and lymphocyte infiltration into the synovium. The resulting synovitis is longlasting and leads to destructive arthritis, which is a hallmark of rheumatoid arthritis. Accumulating evidence suggests that one of the key biochemical events in the altered cell function of RA is phosphorylation of the tyrosine residues of proteins. In this paper we review the cellular components participating in the chronic inflammation of RA joints. We present the results of analyzing tyrosine phosphorylated proteins of synovial cells from RA patients and discuss a possible pathogenic role of non-receptor tyrosine kinase in RA.

A novel 26 kilodalton antigen expressed on the surface membrane of activated T cells

We have identified and characterized the tissue distribution of the antigen recognized by a novel monoclonal antibody (mAb) 1B10, raised against an activated gammadelta T cell clone. Immunohistochemistry of tissue sections, and analysis of single cell suspensions by flow cytometry revealed that mAb 1B10 weakly reacted with <6% of normal human peripheral blood mononuclear cells (PBMC). After 5-6 days of in vitro culture of PBMC activated with phytohemagglutinin (PHA), 55% of the CD4+ and 25% of the CD8+ T cells became 1B10+. 1B10 expression was maintained on long term cultured interleukin 2 (IL-2)-dependent T cell receptor (TCR) alphabeta+ and gammadelta+ clones, and importantly, in contrast to resting T cells, the majority of in vivo activated synovial T lymphocytes from a patient with rheumatoid arthritis were 1B10+. In addition, myelo-monocytic U927 cells, tissue macrophages and some epithelia and fibroblasts were found to react with mAb 1B10. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of molecules immuno-precipitated by mAb 1B10 from radio-iodinated cell surface membrane lysates of T lymphocyte and U937 cells revealed 26 and 29 kiloDalton (kDa) glycoproteins respectively. In conclusion, mAb 1B10 recognizes a novel <<late>> appearing 26 kDa T cell activation antigen that may be useful for further studies of activated T cells in health and disease.

The epidermotropic mycosis fungoides associated alpha1beta1 integrin (VLA-1, CD49a/CD29) is primarily a collagen IV receptor on malignant T cells

Several of the beta1 integrin receptors [very late antigen (VLA) molecules] for extracellular matrix (ECM) proteins are expressed by malignant T cells in cutaneous T-cell lymphoma (CTCL). We evaluated the function of VLA-1, a beta1 integrin specifically expressed in epidermotropic mycosis fungoides (MF), in CD4+ leukemic T cells Jurkat line). We found that Jurkat cells adhere significantly to collagens only after their activation with phorbol 12-myristate 13-acetate (PMA). However, the adhesion to collagen IV (but not to collagen I) of Jurkat cells selected for expressing increased levels of VLA-1 (with unchanged levels of VLA-2, the second collagen integrin receptor) was significantly enhanced relative to that of "VLA-1 low" cells. Monoclonal antibody (mAb) 1B3.1, directed against the collagen binding domain of VLA-1, inhibited adhesion to collagen IV and to collagen I by 36.67%+/-5.25% and 18%+/-4.32%, respectively (p<0.05), whereas the inhibition by anti-VLA-2 mAb PIE6 was comparable on both collagens (25%+/-7.48% and 36.3%+/-0.94%, respectively; p<0.09). Immuno-histochemical studies of skin biopsies from 10 untreated MF patients showed that in all cases at least 10% of the lymphocytes residing in the epidermis are VLA-1+VLA-2-. While not directly applicable to MF, the demonstrated functions of VLA-1 in leukemic Jurkat cells, together with its expression in MF skin, suggest a role for VLA-1 integrins in epidermotropism in a small proportion of leukemic MF cells.

Collagen and collagenase gene expression in three-dimensional collagen lattices are differentially regulated by alpha 1 beta 1 and alpha 2 beta 1 integrins

The reorganization of extracellular matrix (ECM) is an important function in many biological and pathophysiological processes. Culture of fibroblasts in a three-dimensional collagenous environment represents a suitable system to study the underlying mechanisms resulting from cell-ECM interaction, which leads to reprogramming of fibroblast biosynthetic capacity. The aim of this study was to identify receptors that transduce ECM signals into cellular events, resulting in reprogramming of connective tissue metabolism. Our data demonstrate that in human skin fibroblasts alpha 1 beta 1 and alpha 2 beta 1 integrins are the major receptors responsible for regulating ECM remodeling: alpha 1 beta 1 mediates the signals inducing downregulation of collagen gene expression, whereas the alpha 2 beta 1 integrin mediates induction of collagenase (MMP-1). Applying mAb directed against different integrin subunits resulted in triggering the heterodimeric receptors and enhancing the normal biochemical response to receptor ligation. Different signal transduction inhibitors were tested for their influence on gel contraction, expression of alpha 1(I) collagen and MMP-1 in fibroblasts within collagen gels. Ortho-vanadate and herbimycin A displayed no significant effect on any of these three processes. In contrast, genistein reduced lattice contraction, and completely inhibited induction of MMP-1, whereas type I collagen down-regulation was unaltered. Calphostin C inhibited only lattice contraction. Taken together, these data indicate a role of tyrosine-specific protein kinases in mediating gel contraction and induction of MMP-1, as well as an involvement of protein kinase C in the contraction process. The data presented here indicate that different signaling pathways exist leading to the three events discussed here, and that these pathways do not per se depend upon each other.

Monocyte activation: rapid induction of alpha 1/beta 1 (VLA-1) integrin expression by lipopolysaccharide and interferon-gamma

Monocytes play a key role in inflammation, tissue injury and remodelling and wound healing, and most monocyte effector functions are dependent on adhesive interactions. We have analyzed the changes in the pattern of beta 1 integrin expression that take place during monocyte activation and demonstrated that lipopolysaccharide (LPS) and interferon (IFN)-gamma specifically induce the expression of the alpha 1/beta 1 integrin, which was detectable on the monocyte membrane as early as 12 h after monocyte activation. The up-regulated alpha 1/beta 1 expression was not dependent on monocyte adherence to solid surfaces, and Northern blot analysis revealed that LPS and IFN-gamma induce the alpha 1 mRNA de novo. Monocyte deactivating cytokines such as interleukin (IL)-4 or IL-10, could only minimally inhibit the LPS- or IFN-gamma mediated up-regulation of alpha 1/beta 1, suggesting that cytokine release subsequent to monocyte activation does not play a major role in the integrin induction. Interestingly, the LPS-induced expression of alpha 1/beta 1 was found to be dependent on the redox state of the cell, since it was inhibited by antioxidants which also altered the morphological changes that take place during monocyte culture in vitro. The rapid induction of alpha 1 in LPS-activated monocytes suggests that alpha 1/beta 1 might be involved not only in monocyte/extracellular matrix interactions during inflammatory reactions, but also in contributing to further monocyte activation and cytokine production during septic shock syndrome.

Identification of collagen and laminin receptor integrins on murine T lymphocytes

In this study we investigated the receptors by which murine lymphocytes bind to collagen and laminin. To identify the collagen and laminin receptors, we generated three monoclonal antibodies, two of which (HM alpha 1 and HM alpha 2) could inhibit adhesion of activated T cells to collagen and laminin and one of which (HM alpha 6) could inhibit that to laminin. Biochemical studies showed that the antigens recognized by HM alpha 1, HM alpha 2, and HM alpha 6 are the mouse homologues of human VLA-1, VLA-2, and VLA-6, respectively. Finally, we demonstrated that both VLA-1 and VLA-2 contribute to the functional interaction between collagen and activated T cells, since HM alpha 1 and HM alpha 2 specifically inhibited collagen-induced TNF secretion from activated T cells. These results indicate that VLA-1 and VLA-2 play an important role in regulating adhesion and cytokine production of activated T cells.

Differential distribution of intercellular adhesion molecules (ICAM-1, ICAM-2, and ICAM-3) and the MS-1 antigen in normal and diseased human synovia. Their possible pathogenetic and clinical significance in rheumatoid arthritis

OBJECTIVE

Cellular adhesion and differentiation molecules (CAMs) may play a role in the recruitment and retention of inflammatory cells into rheumatoid arthritis synovial tissue (RA ST). In order to determine if certain CAMs are up-regulated in RA ST compared with normal ST, we studied the distribution of intercellular adhesion molecules (ICAMs) 1, 2, and 3 in ST. We also studied the MS-1 antigen since it is preferentially expressed on discontinuous endothelia, such as those found in RA ST; MS-1 is also expressed differentially upon cytokine activation of cells in vitro or in pathologic conditions in situ. Thus, we postulated a possible similarity between MS-1 and ICAM-1 expression in inflamed ST.

METHODS

Immunohistochemical analysis was used to determine the distribution of ICAMs and MS-1 in ST from 10 patients with RA, 10 with osteoarthritis (OA), and 4 normal individuals.

RESULTS

ICAM-1 expression was found on significantly more RA ST endothelial cells compared with normal cells, as well as on RA ST macrophages and lining cells. ICAM-2, also found on endothelial cells, showed no differential staining pattern. ICAM-3 was present on RA ST macrophages and lining cells as well as on some RA and OA endothelial cells. The MS-1 antigen was present on most RA and OA ST endothelia, lining cells, and macrophages. ICAM-1 expression and MS-1 expression in the lining layer were positively correlated in both RA and OA.

CONCLUSION

ICAM-1, while found mainly on endothelial cells, is up-regulated on RA ST macrophages and lining cells, suggesting a role for these cells in the infiltration and tissue damage seen in the RA ST: ICAM-3, which is present mainly on normal resting leukocytes but not on normal endothelium, is expressed by some diseased ST leukocytes and endothelial cells. MS-1 is also found on the RA ST specialized, fenestrated endothelium, on macrophages, and in the lining layer. These results suggest that the differential expression of ICAMs and MS-1 in RA ST compared with normal ST might play a special role in the pathogenesis of RA.

Increased expression of VLA-5 adhesion molecules on synovial fluid T lymphocytes in chronic polyarthritis: a consequence of T-cell activation

This study focuses on the consequences of T-lymphocyte activation in chronic polyarthritis in terms of expression of cell surface receptors interacting with extracellular matrix (ECM). The expression of the VLA group of integrins was studied on in vitro-stimulated peripheral-blood T cells, and on peripheral-blood and synovial-fluid mononuclear cells (MNC) of patients with polyarthritis. The VLA expression was measured by flow cytometry using monoclonal antibodies (MoAbs) against alpha-subunits of the VLA family. VLA-alpha 4 and VLA-alpha 5, but not VLA-alpha 1, were expressed on a major fraction of unstimulated peripheral-blood T cells both in the patients with polyarthritis and in healthy individuals. Two distinct populations, VLA-alpha 5-high and VLA-alpha 5-low, were found in resting peripheral-blood T lymphocytes. Two days after stimulation by phorbol 12-myristate 13-acetate (PMA) and concanavalin A, most T cells became VLA-alpha 5-high. In patients with chronic polyarthritis, the expression of VLA-alpha 1 and VLA-alpha 5 was always higher on synovial-fluid T cells than on peripheral-blood T cells. These results give further support to the hypothesis that upon activation the induction of the VLA adhesion-molecule expression may be a factor contributing to the accumulation of T cells in the inflamed synovium.

Clonal V alpha 12.1+ T cell expansions in the peripheral blood of rheumatoid arthritis patients

Rheumatoid arthritis (RA) represents a heterogenous disease characterized by chronic polyarthritis. Most patients with adult RA inherit HLA-DR4 or -DR1 major histocompatibility complex (MHC) genes. While the molecular basis for this genetic predisposition is unknown, the major function of these MHC-encoded molecules is to present peptides to T lymphocytes. It is hypothesized that an endogenous or environmental antigen initiates a MHC-restricted immune response mediated by T lymphocytes, which is followed by a chronic inflammatory reaction involving many cell types. In chronic RA, previous or ongoing antigenic activation might result in detectable skewing of the peripheral alpha/beta T cell receptor (TCR) repertoire. Here we demonstrate a marked expansion of V alpha 12.1-bearing CD8+ T cells in the peripheral blood (mean, 22%; range, 10-43%) of > 15% of RA patients. A major proportion of these patients shared HLA-DQ2 in addition to the expected high frequency DR1 and DR4 alleles. Detailed molecular analysis in three of the RA patients with elevated V alpha 12.1+ T cells identified repeated TCR alpha chain sequences consistent with clonal V alpha 12.1+,CD8+ T cell expansion. In addition to shared TCR V alpha 12.1 germline gene usage among unrelated subjects, a conserved J alpha motif was also detected. Together, these results suggest an antigen-driven mechanism of T cell expansion in these patients and may offer a new approach in examining specific antigen that stimulate T cells in RA.

Expression of very late activation antigen-1 on intrathyroid lymphocytes in autoimmune thyroid disease

Very late activation antigen-1 (VLA-1) is a beta 1-integrin implied in interaction with extracellular matrix components. It is expressed by T lymphocytes upon prolonged activation in vitro. In this work we have evaluated VLA-1 expression in thyroid infiltrates and peripheral blood of patients with autoimmune thyroid disease (AITD), by immunofluorescence on dispersed cells and by in situ analysis on frozen tissue sections. The results obtained showed increased proportions of VLA-1 positive lymphocytes in thyroid infiltrates, similarly to that observed with "early" activation antigens. No positivity of thyroid follicular cells was observed. Given the role of the VLA-1 molecule in lymphocyte adhesion, the increased VLA-1 positivity of infiltrating lymphocytes is consistent with intrathyroidal homing of long-term activated cells, possibly relevant to AITD pathogenesis.