Characterisation of the cell type-specificity of collagenase 3 mRNA expression in comparison with membrane type 1 matrix metalloproteinase and gelatinase A in the synovial membrane in rheumatoid arthritis

OBJECTIVE

To study the pattern and cell type-specificity of collagenase 3, membrane-type 1 matrix metalloproteinase (MT1-MMP), and gelatinase A mRNA expression in the synovial membrane in rheumatoid arthritis (RA).

METHODS

The mRNA expression of collagenase 3, MT1-MMP, and gelatinase A was characterised by northern blot analysis, reverse transcriptase-polymerase chain reaction, and in situ hybridisation. In situ hybridisation was performed in combination with the immunohistochemical detection of cell type-specific antigens.

RESULTS

Synovial membrane specimens from 19 of 21 patients with RA expressing collagenase 3 mRNA were positive for MT1-MMP and gelatinase A mRNA. In control samples from patients without destructive inflammatory joint diseases collagenase 3 mRNA was not expressed and only in two of seven cases was a coexpression of MT1-MMP and gelatinase A mRNA detected. Fibroblast-like cells of the synovial membrane were found to be the predominant source of collagenase 3, MT1-MMP, and gelatinase A mRNA expression in lining and sublining layers as well as at the synovial membrane-cartilage interface. Additionally, the expression of MT1-MMP mRNA was detected in endothelial cells. Collagenase 3 mRNA expression was found in about 5% of CD68 positive macrophages.

CONCLUSIONS

Collagenase 3 mRNA is expressed simultaneously with MT1-MMP and gelatinase A mRNA in fibroblast-like cells of the synovial membrane in RA. These results suggest (a) a broad extracellular proteolytic potential of fibroblast-like cells and (b) an important role of cell surface associated procollagenase 3 activation by MT1-MMP and gelatinase A for cartilage degradation by invading fibroblast-like cells.

Expression of lymphotoxin-alpha by keratinocytes: a further mediator for the lichenoid reaction

OBJECTIVE

Lichen planus (LP) represents a disease in which autoimmune mechanisms mediated by Th1 T cells are involved. Lymphotoxin-alpha (LT-alpha) represents a Th1 cytokine with proinflammatory activities in LP, as has recently been demonstrated for interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha).

METHODS

Expression of LT-alpha mRNA was investigated by RT-PCR and nonradioactive in situ hybridization. Double staining methods were applied to characterize the phenotype of cells expressing LT-alpha. Cell stimulation experiments were performed on the transformed squamous cell line HaCaT.

RESULTS

In contrast to normal skin, LT-alpha-specific RT-PCR products were found in all cases of LP. Cells in the inflammatory infiltrate expressing LT-alpha were identified as mainly T cells and mast cells, as shown by in situ hybridization. Furthermore, predominant LT-alpha mRNA expression could be observed in lesional keratinocytes adjacent to the band-like inflammatory infiltrate. In cell stimulation experiments, it could be shown that IFN-gamma induces LT-alpha and TNF-alpha mRNA in the human squamous cell line HaCaT, concomitant with upregulation of MHC class II and intercellular adhesion molecule-1, which could also be observed on lesional keratinocytes in LP.

CONCLUSIONS

In LP, LT-alpha mRNA is predominantly expressed by lesional keratinocytes and to a lesser extent by inflammatory cells. Induction of LT-alpha in keratinocytes is closely related to the expression of TNF-alpha and MHC class II. The loci of TNF-alpha and LT-alpha map to MHC class III on chromosome 6, which is closely linked to the MHC class II gene locus. Our results suggest that stimulation of keratinocytes with IFN-gamma results in the upregulation of proinflammatory cytokines such as LT-alpha and TNF-alpha as well as MHC class II, which map to the same gene region of immunoregulatory genes on chromosome 6 and may be involved in the induction and maintenance of the disease.

Synovial tissue protease gene expression and joint erosions in early rheumatoid arthritis

OBJECTIVE

To relate the expression of proteases in the lining and sublining layers of the synovial membrane to the rate of joint damage during 1 year in patients with early inflammatory arthritis.

METHODS

Samples of synovial membrane were obtained by closed-needle biopsy or needle arthroscopy from inflamed knees of 20 patients with early inflammatory polyarthritis (mean disease duration 9.6 months, range 2 weeks to 18 months). Expression of matrix metalloproteinase 1 (MMP-1), cathepsin B (CB), and cathepsin L (CL) was examined using in situ hybridization. Immunohistochemistry was used to identify infiltrating mononuclear cell populations. Radiographs of the hands and feet, performed at presentation and after 1 year, were evaluated for the development of new erosions.

RESULTS

Twelve patients had rheumatoid arthritis (RA), 6 had psoriatic arthritis (PsA), 1 had gout, and 1 had an undifferentiated arthritis. Six patients had erosions at presentation. Eleven patients (10 with RA, 1 with PsA) demonstrated at least 1 new erosion after 1 year of followup. MMP-1, CB, and CL messenger RNA (mRNA) were expressed in the synovial membrane of all patients and were present throughout the lining layer, as well as in perivascular cellular infiltrates and endothelial cells in the sublining layer. In the lining layer, the mean percentages of protease mRNA-positive cells per high-power field were higher in those patients who developed new joint erosions than in those without evidence of joint damage. A similar pattern was observed in the sublining layer, where mean numbers of protease mRNA-positive cells were also greater in patients with new joint erosions. There were significant differences between the two groups in MMP-1 mRNA expression in both the lining and sublining layers (P = 0.0007 and P = 0.0027, respectively), as well as in sublining layer CL mRNA expression (P = 0.017), but not in CB mRNA expression. Numbers of lining layer CD68+ cells correlated positively with lining layer MMP-1 mRNA expression (P = 0.043) and with the development of new joint erosions (P = 0.002).

CONCLUSION

The detection of MMP-1, CB, and CL in the synovium soon after the onset of symptoms highlights the potential for early joint destruction in patients with RA. High levels of MMP-1 mRNA expression in the lining layer distinguished patients with more rapidly progressive erosive disease. This is the first study to demonstrate features of early synovial pathophysiology that may identify patients at increased risk of developing new joint erosions.

Expression of osteopontin messenger RNA and protein in rheumatoid arthritis: effects of osteopontin on the release of collagenase 1 from articular chondrocytes and synovial fibroblasts

OBJECTIVE

Osteopontin (OPN) is an extracellular matrix protein that has been implicated in the interactions between tumor cells and host matrix, including those involved in invasion and spread of tumor cells. Because joint destruction in rheumatoid arthritis (RA) is mediated by the invasive growth of synovial tissue through its attachment to cartilage, we examined the expression of OPN in the synovia of patients with RA and the effect of OPN on the production of collagenase 1 in rheumatoid synovial fibroblasts and articular chondrocytes.

METHODS

The expression of OPN messenger RNA (mRNA) and protein in synovia from 10 RA patients was examined by in situ hybridization and immunohistochemistry. Synovial fibroblasts from RA patients and articular chondrocytes from patients without joint disease were cultured in the presence of various concentrations of OPN, and levels of collagenase 1 in the culture supernatants were measured by enzyme-linked immunosorbent assay.

RESULTS

The expression of OPN mRNA and protein was observed in 9 of 10 specimens obtained from patients with RA. OPN was expressed in the synovial lining and sublining layer and at the interface of cartilage and invading synovium. Double labeling revealed that the majority of OPN-expressing cells were positive for the fibroblast-specific enzyme prolyl 4-hydroxylase and negative for the macrophage marker CD68, while only a few, single OPN-expressing cells were positive for CD68 at sites of synovial invasion into cartilage. OPN staining was not observed in lymphocytic infiltrates or leukocyte common antigen (CD45)-positive cells. Three of 3 cultures of human articular chondrocytes secreted detectable basal amounts of collagenase, with a dose-dependent increase upon OPN stimulation, while synovial fibroblast cultures produced much lower levels of collagenase, with only 2 of 4 fibroblast cultures responding in a dose-dependent manner.

CONCLUSION

These findings suggest that OPN produced by synovial fibroblasts in the synovial lining layer and at sites of cartilage invasion not only mediates attachment of these cells to cartilage, but also contributes to matrix degradation in RA by stimulating the secretion of collagenase 1 in articular chondrocytes.

Increased serum levels of non-collagenous matrix proteins (cartilage oligomeric matrix protein and melanoma inhibitory activity) in marathon runners

OBJECTIVE

Marathon runners have an increased risk of developing joint disease. During and after a 42-km run, elevation of multiple cytokines occurs in the blood, reflecting inflammatory processes. We compared this cytokine response with serum levels of cartilage oligomeric matrix protein (COMP) and melanoma inhibitory activity (MIA), two markers for joint metabolism and/or damage.

METHODS

Serum from eight endurance-trained runners was collected shortly before the start of a marathon run, after 31 km, 42 km, 2 h after the end, on the first and on the second morning after the run. For comparison, serum was obtained from 35 healthy controls and 80 patients with knee joint injury, rheumatoid arthritis or osteoarthritis. Serum levels of C-reactive protein (CRP), interleukin-1beta (IL-1beta), interleukin-1 receptor antagonist (IL-1RA), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), soluble interleukin-6 receptor (sIL-6R, gp80), soluble tumor necrosis factor receptor II (sTNFRII, p75), COMP and MIA were measured by ELISA.

RESULTS

Compared with healthy controls, the runner's baseline serum levels of TNF-alpha, sIL-6R, COMP and MIA were significantly increased. COMP and MIA levels, higher than the upper normal limits of 5 microg/ml and 6 ng/ml respectively, were found in seven and five of eight runners. The elevated levels of COMP were similar to those found in joint injury or osteoarthritis, and the elevated levels of MIA were comparable to those reported in rheumatoid arthritis. During the run, the serum levels of IL-1RA, IL-6, TNF-alpha and COMP rose significantly, and gradually returned to baseline within 24 h. Only modest changes of CRP, sIL-6R, sTNFRII and MIA occurred during the run. Late elevations of CRP and MIA were observed after 24 and 48 h. The correlation analysis suggests associations between COMP, sIL-6R, TNF-alpha, IL-1RA on one hand and sTNFRII, and MIA and CRP on the other hand.

CONCLUSIONS

Elevated baseline levels of COMP and MIA might reflect increased joint matrix turnover and/or damage due to prior extreme physical training. During the run, COMP was increasing possibly due to the severe physical strain on joint structures, associated with the early inflammation. After the run, MIA and CRP increased within 24 h, suggesting a correlation with later inflammatory processes. Thus, our data suggest that COMP and MIA are markers for distinct aspects of joint metabolism and/or damage in both disease and sport.

Expression of sentrin, a novel antiapoptotic molecule, at sites of synovial invasion in rheumatoid arthritis

OBJECTIVE

Sentrin, a novel antiapoptotic molecule, has been shown to interact with the signal-competent form of Fas/APO-1 and tumor necrosis factor receptor I (TNFRI), and thereby, to protect cells against anti-Fas/APO-1- and TNF-induced cell death. Since reduced apoptosis in the synovial lining is supposed to contribute to synovial hyperplasia in rheumatoid arthritis (RA), we searched for the expression of sentrin-1 messenger RNA (mRNA) in synovium from patients with RA.

METHODS

The expression of sentrin-1 mRNA was examined by in situ hybridization on snap-frozen sections of normal and RA synovial tissues as well as on paraffin-embedded RA synovial specimens, including the interface of cartilage-bone and invading synovium. Immunohistochemical double labeling after in situ hybridization was performed to further characterize sentrin-1 mRNA-expressing cells. In addition, quantitative analysis of sentrin-1 mRNA expression in RA synovial fibroblasts (RASF), osteoarthritis synovial fibroblasts (OASF), and normal fibroblasts was performed by quantitative real-time polymerase chain reaction. Expression levels were standardized to the expression of GAPDH. The in vivo maintenance of sentrin expression in RASF aggressively invading human cartilage was explored in the SCID mouse model of RA.

RESULTS

A marked expression of sentrin-1 mRNA could be seen in all RA synovial specimens, predominantly in SF of the lining layer and at sites of invasion of RA synovium into cartilage. In normal synovial tissues, no sentrin-1 mRNA was detectable. RASF showed a maximum 32.5-fold (mean +/- SD 14.9 +/- 11.6) increase of sentrin-1 mRNA expression compared with normal fibroblasts and a maximum 31.4-fold (mean +/-SD 14.3 +/- 10.9) increase compared with OASF. When coimplanted with normal human cartilage in the SCID mouse model, invading RASF maintained their sentrin-1 mRNA expression for at least 60 days in vivo.

CONCLUSION

The marked expression of sentrin in rheumatoid synovial tissue, but not in normal or OA synovial tissue, may contribute to the modulation of Fas- and TNFR-mediated apoptosis in RA synovium, and thereby extend the lifespan of invasive, cartilage-destructive SF.

Increased expression of CD40 ligand (CD154) on CD4+ T cells as a marker of disease activity in rheumatoid arthritis

OBJECTIVES

The interaction between the activation induced surface glycoprotein CD40L (ligand) (CD154) on CD4+ T cells and its receptor CD40, which is expressed on various cell types, plays a crucial part in numerous cell mediated and humoral immune reactions that may be of pathogenetic importance in rheumatoid arthritis (RA). To further evaluate the pathogenetic role of CD40L in RA, expression of CD40L and various other T cell activation antigens as well as costimulatory molecules was investigated on CD4+ T cells in RA by flow cytometry.

METHODS

Two colour flow cytometry was used to determine the percentage of CD4+ T cells expressing CD40L, CD69, CD25, HLA-DR, CD39, CD27 and CD28 in peripheral blood (PB) of 62 RA patients in comparison to 20 healthy controls (HC). Disease activity was assessed by clinical, laboratory and radiological examination. Status of clinical remission of RA was evaluated according to the ACR preliminary criteria for complete clinical remission of RA.

RESULTS

CD40L was expressed on > 10% of CD4+ T cells in 29% of RA patients thus defining a CD40L(high+) patient group. Disease activity as estimated by C reactive protein, rheumatoid factor and status of clinical remission of disease (p = 0.049) was higher in this subgroup than in the RA CD40L(low+) group. Expression of CD69, CD25, and HLA-DR was significantly increased in both RA patient groups in comparison with HC. However, the percentage of CD39+ CD4+ T cells was increased only in the RA CD40L(high+) subgroup (versus HC p = 0.019, versus RA CD40L(low+) p = 0.044). Furthermore, expression of CD40L and CD39 on CD4+ T cells correlated positively as estimated by Spearman rank correlation (p<0.001). The percentage of CD4+ T cells lacking the costimulatory molecules CD27 (p = 0.002) and CD28 (p = 0.026) was increased in RA CD40L(low+) patients in comparison with HC.

CONCLUSIONS

These data suggest that increased expression of CD40L on CD4+ T cells in RA indicates prolonged and increased activation of CD4+ T lymphocytes and is associated with active disease and possibly an unfavourable prognosis. Whether this phenotypically defined RA CD40L(high+) subgroup will preferentially respond to an anti-CD40L antibody treatment remains to be elucidated.

Membrane-type-1 matrix metalloproteinase is abundantly expressed in fibroblasts and osteoclasts at the bone-implant interface of aseptically loosened joint arthroplasties in situ

OBJECTIVE

To investigate the distribution pattern of membrane-type-1 matrix metalloproteinase (MT1-MMP) within the synovial-like interface membranes of failed prosthetic joints.

METHODS

Interface tissue around loose arthroplasties containing both fibrous membrane and attached bone was obtained from 6 patients at revision surgery. In situ hybridization with digoxigenin labeled RNA probes was applied to investigate MT1-MMP expression in paraffin sections of the samples. In addition, double labeling using immunohistochemistry was performed to characterize MT1-MMP producing cells.

RESULTS

Apart from being present in fibroblasts, MT1-MMP was also found expressed in osteoclasts at sites of bone resorption. Our results revealed no expression of MT1-MMP at parts of the membrane that originally had been located next to the prosthesis. In contrast, abundant staining for MT1-MMP was observed at sites attached to bone. MT1-MMP mRNA expression was more intense at those sites of bone resorption covered by a thicker interface membrane.

CONCLUSION

These results indicate a role for MT1-MMP not only in matrix degradation by fibroblasts but also in osteoclast mediated bone resorption. Given the ability of MT1-MMP to activate MMP2 and MMP13, they suggest also that osteoclasts might contribute to matrix degradation by activating these MMP. This could be of potential interest not only for other conditions in which bone resorption by fibroproliferative tissue plays a role, but also to design novel strategies to prevent loosening of prosthetic joints.

Collagenase, cathepsin B and cathepsin L gene expression in the synovial membrane of patients with early inflammatory arthritis

OBJECTIVE

To examine the expression of the matrix metalloproteinase, MMP-1, and the cysteine proteases, cathepsin B (CB) and cathepsin L (CL), in the synovial membrane (SM) of patients with early inflammatory arthritis.

METHODS

Samples of SM were obtained by blind needle biopsy or needle arthroscopy from inflamed knees of 28 patients with early inflammatory arthritis (mean disease duration 10.2 months, range 2 weeks-18 months). Sixteen patients had rheumatoid arthritis (RA), nine psoriatic arthritis and there was one each with ankylosing spondylitis, gout and an undifferentiated arthritis. Comparison was made with tissue from two patients with established erosive RA and three normal synovial tissue samples. In situ hybridization was performed using digoxigenin-labelled RNA probes.

RESULTS

MMP-1, CB and CL were expressed in all patients with early arthritis and in established erosive RA, whereas normal synovium showed only scanty expression. The three proteases were prominent in perivascular infiltrates and endothelial cells of early arthritis tissue. MMP-1 was observed primarily in the lining layer, but was also evident in the sublining area. CB and CL were expressed to a lesser extent in the lining layer, and were present mainly in the subintima. The three proteases were not found in lymphoid aggregrates. No differences were observed between the disease categories.

CONCLUSIONS

The detection of MMP-1, CB and CL in the synovium shortly after symptom onset implies that the potential for joint destruction exists at a very early stage in the disease. In addition, the perivascular and endothelial cell expression suggests a role for these proteases in mononuclear cell influx to the inflamed synovium and in angiogenesis.

Cysteine proteinase cathepsin K mRNA is expressed in synovium of patients with rheumatoid arthritis and is detected at sites of synovial bone destruction

OBJECTIVE

Cysteine proteinases B and L have been shown to be involved in matrix degradation of joints in patients with rheumatoid arthritis (RA). Since the cysteine proteinase cathepsin K is assumed to play a pivotal role in osteoclast mediated bone resorption, we investigated the expression of cathepsin K in RA joints.

METHODS

We studied 10 RA and 4 normal synovial specimens and 5 articular heads with RA lesions by in situ hybridization, applying specific riboprobes for cathepsin K, human collagen type I, and cathepsin B. Antibodies against monocyte/macrophage associated CD68 antigen were applied in immunohistochemistry. Reverse transcription-polymerase chain reaction (RT-PCR) and ribonuclease protection assay (RPA) were performed on 4 RA, 1 normal, and 1 immortalized normal fibroblast cultures.

RESULTS

Cathepsin K mRNA expression was upregulated in RA synovium compared to normal synovium. Cathepsin K mRNA was expressed mainly by synovial fibroblasts. These data were confirmed by RT-PCR and RPA. In RA articular heads, cathepsin K mRNA was detected at sites where synovium attached and invaded underlying bone. The cells at these sites represented collagen type I and cathepsin B mRNA expressing fibroblasts as well as CD68+ macrophages and giant cells. In addition, a distinct expression of cathepsin K mRNA was also detected around lymphocytic infiltrates in RA synovium.

CONCLUSION

The data indicate that cathepsin K is not only expressed by osteoclasts but also by synovial fibroblasts, and suggest that cathepsin K contributes to bone destruction mediated by RA synovial cells. The expression of cathepsin K around lymphocytic infiltrates suggests further to facilitate the movement of mononuclear cells through the perivascular interstitial matrix and thereby contribute to interstitial matrix turnover.

Interleukin-16, produced by synovial fibroblasts, mediates chemoattraction for CD4+ T lymphocytes in rheumatoid arthritis

The massive infiltration of synovium with CD4+ T cells during the course of rheumatoid arthritis (RA) implies the expression of chemoattractant factors by resident synovial cells. Therefore, we analyzed the expression of IL-16, a potent chemoattractant for CD4+ T cells, to account for the accumulation of CD4+ T cells in RA. Indeed, IL-16 was found to be significantly elevated in synovial fluid (SF) from patients with RA as compared to non-RA arthritis (p < 0.001), osteoarthritis (p < 0.001) and controls (p < 0.001). Chemotaxis studies showed IL-16 to contribute to the strong chemotactic activities of RA-SF. In situ hybridization (ISH) revealed IL-16 mRNA-expressing cells located within the lining layer of rheumatoid synovial tissue. In the sublining area, only scattered IL-16 transcript-positive cells could be detected, mainly adjacent to blood vessels. By a double-labeling technique, combining ISH for IL-16 mRNA and immunohistochemistry for CD68, synovial fibroblast-like, CD68-negative cells were identified as a major source of IL-16 mRNA within RA synovium. This study demonstrates that synovial fibroblasts produce IL-16 in RA and thus mediate chemoattraction of CD4+ cells into synovial tissue.

Analysis of cartilage oligomeric matrix protein (COMP) in synovial fibroblasts and synovial fluids

We investigated the expression of cartilage oligomeric matrix protein (COMP) in normal and rheumatoid arthritis (RA) synovial fibroblasts. In situ hybridization (ISH) was conducted on synovial specimens from five RA patients applying specific probes for COMP or fibroblast collagen type I. ISH was combined with immunohistochemistry, applying antibodies to the macrophage marker CD68. Ribonuclease protection assay (RPA) and rapid amplification of 3'-cDNA ends (3'-RACE) were performed on total RNA from normal and RA synovial fibroblast cultures. Protein extracts from fibroblasts and culture supernatants were compared with synovial fluids and protein extracts from isolated chondrocytes by Western blot utilizing polyclonal and monoclonal antibodies (18-G3 mAb) to COMP. COMP mRNA was detected in fibroblasts of RA synovium by ISH, and in normal and RA synovial fibroblast cultures by RPA. 3'-RACE demonstrated sequence homology of chondrocyte and synovial fibroblast COMP along the coding sequence. COMP protein was detected in synovial fibroblasts and culture supernatants by immunoblot. Using polyclonal antibodies, the major portion of COMP from fibroblasts and culture supernatants was present as low-molecular-weight (LMW) bands, corresponding to those found in synovial fluids. These LMW COMP bands, however, were not detected in any of the cells or tissues tested using 18-G3 mAb. In protein extracts from chondrocytes and in COMP purified from cartilage, these LMW bands could not be detected. In conclusion, the data suggest that certain forms of COMP detected in synovial fluid are secreted from synovial fibroblasts and could be distinguished by specific mAbs from COMP secreted by chondrocytes.

Mechanism of joint destruction in rheumatoid arthritis

The synovium in rheumatoid arthritis (RA) is characterized by an increase in lining layer thickness and infiltration of inflammatory cells into the sublining area. Fibroblasts in the lining layer develop the appearance of "transformed cells", under the influence of proto-oncogenes involved in the regulation of the cell cycle. Fibroblast and macrophage-derived cytokines such as IL-1 and TNF-alpha are present abundantly in the rheumatoid synovium and stimulate these cells to produce destructive enzymes. Other cytokines such as IL-4 and IL-10 represent a physiological attempt to reverse the inflammatory process. Adhesion molecules facilitate both the migration of cells to the joint as well as the attachment of synovium to bone and cartilage. Joint destruction is mediated by enzymes such as serine proteases, matrix metalloproteinases (MMPs) and the cathepsins. Treatments directed against various components of the inflammatory cascade have shown promise. Inhibition of MMPs or adhesion molecules, blockade of IL-1 or TNF-alpha and the use of anti-Fas antibodies to induce apoptosis offer new possibilities for the treatment of RA. More recently, the employment of genes with antiarthritic properties has shown therapeutic potential.

TNF-alpha-mediated expression of the receptor for anaphylatoxin C5a on neurons in experimental Listeria meningoencephalitis

The anaphylatoxin C5a has been implicated in the pathogenesis of bacterial meningitis as a potent mediator of inflammation in the subarachnoid space. We investigated the expression of the receptor for C5a (C5aR) in brains of mice with experimental Listeria monocytogenes (LM) meningoencephalitis. In the course of the disease, infiltrating cells in the meninges and the ventricles were found to express C5aR mRNA and protein. In the brain parenchyma, very low constitutive C5aR expression was seen on pyramidal neurons and Purkinje cells. However, in LM-infected mice, a dramatic increase in C5aR expression occurred on neurons starting 6 h after infection and was maximal between 24 and 36 h. TNF-alpha was identified as an essential mediator of neuronal C5aR expression, since mice lacking the genes for TNF and lymphotoxin-alpha (TNF/lymphotoxin-alpha -/- mice) showed significantly attenuated C5aR expression after LM infection. Furthermore, i.p. injection of recombinant TNF-alpha induced enhanced C5aR expression in the brains of TNF/lymphotoxin-alpha -/- mice and in normal animals even in the absence of a bacterial infection. We also assessed the levels of anaphylatoxin C5a in the cerebrospinal fluid of patients with infectious meningitis. C5a was detected in all patients with bacterial meningitis (n = 9), in 6 of 18 patients with aseptic meningitis, and in 1 of 66 control patients. The finding of TNF-alpha-mediated C5aR expression on neurons in experimental Listeria meningitis and the detection of the ligand, C5a, in the cerebrospinal fluid of human patients with infectious meningitis present new directions in the investigation of the pathophysiologic sequelae leading to secondary brain damage.

TNF-alpha-mediated expression of the receptor for anaphylatoxin C5a on neurons in experimental Listeria meningoencephalitis

The anaphylatoxin C5a has been implicated in the pathogenesis of bacterial meningitis as a potent mediator of inflammation in the subarachnoid space. We investigated the expression of the receptor for C5a (C5aR) in brains of mice with experimental Listeria monocytogenes (LM) meningoencephalitis. In the course of the disease, infiltrating cells in the meninges and the ventricles were found to express C5aR mRNA and protein. In the brain parenchyma, very low constitutive C5aR expression was seen on pyramidal neurons and Purkinje cells. However, in LM-infected mice, a dramatic increase in C5aR expression occurred on neurons starting 6 h after infection and was maximal between 24 and 36 h. TNF-alpha was identified as an essential mediator of neuronal C5aR expression, since mice lacking the genes for TNF and lymphotoxin-alpha (TNF/lymphotoxin-alpha -/- mice) showed significantly attenuated C5aR expression after LM infection. Furthermore, i.p. injection of recombinant TNF-alpha induced enhanced C5aR expression in the brains of TNF/lymphotoxin-alpha -/- mice and in normal animals even in the absence of a bacterial infection. We also assessed the levels of anaphylatoxin C5a in the cerebrospinal fluid of patients with infectious meningitis. C5a was detected in all patients with bacterial meningitis (n = 9), in 6 of 18 patients with aseptic meningitis, and in 1 of 66 control patients. The finding of TNF-alpha-mediated C5aR expression on neurons in experimental Listeria meningitis and the detection of the ligand, C5a, in the cerebrospinal fluid of human patients with infectious meningitis present new directions in the investigation of the pathophysiologic sequelae leading to secondary brain damage.