Cysteine peptidases of mammals: their biological roles and potential effects in the oral cavity and other tissues in health and disease

Cysteine peptidases (CPs) are phylogenetically ubiquitous enzymes that can be classified into clans of evolutionarily independent proteins based on the structural organization of the active site. In mammals, two of the major clans represented in the genome are: the CA clan, whose members share a structure and evolutionary history with papain; and the CD clan, which includes the legumains and caspases. This review focuses on the properties of these enzymes, with an emphasis on their potential roles in the oral cavity. The human genome encodes at least (but possibly no more than) 11 distinct enzymes, called cathepsins, that are members of the papain family C1A. Ten of these are present in rodents, which also carry additional genes encoding other cathepsins and cathepsin-like proteins. Human cathepsins are best known from the ubiquitously expressed lysosomal cathepsins B, H, and L, and dipeptidyl peptidase I (DPP I), which until recently were considered to mediate primarily "housekeeping" functions in the cell. However, mutations in DPP I have now been shown to underlie Papillon-Lefevre syndrome and pre-pubertal periodontitis. Other cathepsins are involved in tissue-specific functions such as bone remodeling, but relatively little is known about the functions of several recently discovered enzymes. Collectively, CPs participate in multiple host systems that are active in health and in disease. They are involved in tissue remodeling and turnover of the extracellular matrix, immune system function, and modulation and alteration of cell function. Intracellularly, CPs function in diverse processes including normal protein turnover, antigen and proprotein processing, and apoptosis. Extracellularly, they can contribute directly to the degradation of foreign proteins and the extracellular matrix. However, CPs can also participate in proteolytic cascades that amplify the degradative capacity, potentially leading to pathological damage, and facilitating the penetration of tissues by cancer cells. We know relatively little regarding the role of human CPs in the oral cavity in health or disease. Most studies to date have focused on the potential use of the lysosomal enzymes as markers for periodontal disease activity. Human saliva contains high levels of cystatins, which are potent CP inhibitors. Although these proteins are presumed to serve a protective function, their in vivo targets are unknown, and it remains to be discovered whether they serve to control any human CP activity.

Immunohistochemical localization of cathepsin L and cystatin A in normal skin and skin tumors

Cathepsin L, a cysteine proteinase, and cystatin A, an inhibitor of cysteine proteinases, are thought to regulate the invasion and metastasis of malignant cells. In this study, the expression of cathepsin L and cystatin A in skin tumors was investigated immunohistochemically in order to examine the relationship between these two enzymes in the pathophysiology of malignant cells. Formalin-fixed and paraffin embedded specimens from normal skin, seborrheic keratoses, and squamous cell carcinomas were reacted with polyclonal antibodies against rat cathepsin L or cystatin a which cross-react to human cathepsin L and cystatin A, respectively. The consequent immunostaining of these enzymes was observed to be strong in normal skin (4 cases) and seborrheic keratosis (6 cases). In well-differentiated squamous cell carcinoma (SCC) (9 cases), staining for cathepsin L and cystatin A was moderately positive in differentiated tumor cells and negative in undifferentiated SCC (5 cases). The degree of staining of these enzymes was inversely correlated with the differentiation of the malignant cells. These results suggest that the immunohistochemical analysis of cathepsin L and cystatin A is a useful indicator for an aspect of malignancy in human epidermal keratinocytes.

Identification and characterization of cystatin-related epididymal spermatogenic protein in human spermatozoa: localization in the equatorial segment

Our earlier studies in mouse have shown that the cystatin-related epididymal spermatogenic (CRES) protein is highly expressed in elongating spermatids in the testis and is present in mouse sperm acrosomes, suggesting specific roles in sperm function, fertilization, or both. However, whether the human CRES gene is similar to that of the mouse and is expressed in germ cells has not yet been determined. Therefore, the present study was undertaken to characterize the human ortholog of mouse CRES: Northern blot and in situ hybridization experiments showed that CRES is highly expressed in the human testis, specifically within clusters of round spermatids. Furthermore, reverse transcription-polymerase chain reaction detected CRES mRNA in the epididymis. Western blot analysis of protein lysates prepared from human testis and ejaculated spermatozoa showed a predominant 19-kDa protein and a minor 14-kDa protein. However, in contrast to the acrosomal localization of CRES protein in mouse spermatozoa, indirect immunofluorescence of human spermatozoa treated with methanol/acetic acid using anti-human CRES antibodies revealed that CRES was strictly localized to the equatorial segment. Furthermore, the same staining was observed in both capacitated and acrosome-reacted spermatozoa. To determine whether CRES was associated with the plasma membrane, live spermatozoa were incubated with CRES antibody after capacitation and acrosome reaction. Only acrosome-reacted spermatozoa showed a weak but specific equatorial staining. Taken together, these studies show that CRES protein is present in the sperm equatorial segment and becomes accessible to the extracellular environment during fertilization.

Cystatin M / E expression in inflammatory and neoplastic skin disorders

BACKGROUND

Cystatins are natural and specific inhibitors of endogenous mammalian lysosomal cysteine proteinases and exogenous microbial cysteine proteinases. Cystatins were shown to provide regulatory and protective functions against uncontrolled proteolysis in several disease processes. Recently we reported that cystatin M/E, which is a novel member of the cystatin gene family, has an unusually restricted expression pattern that is limited to skin. Although cystatin M/E possesses two distinct biochemical properties (it is a proteinase inhibitor and a substrate for transglutaminase) its physiological function is unknown. Disturbance of the balance between proteinases and their inhibitors can lead to irreversible damage as in chronic inflammatory reactions and tumour invasion.

OBJECTIVES

To examine the expression pattern of cystatin M/E in inflammatory conditions and neoplastic skin disorders in order to obtain possible clues on its function. Furthermore, we wished to determine whether cystatin M/E expression could discriminate between various types of neoplasia.

METHODS

Biopsy material of normal skin, atopic dermatitis and psoriatic lesional skin, healing excisional wounds in healthy volunteers, and several types of epidermal neoplasia (keratoacanthoma, actinic keratosis, basal cell carcinoma and squamous cell carcinoma) were used in this study. For comparison we studied the expression of cystatin M/E in squamous neoplasias from non-cutaneous origin. Affinity-purified polyclonal antibodies against cystatin M/E were used for immunohistochemical detection.

RESULTS

Cystatin M/E is constitutively expressed in the stratum granulosum of normal skin, sebaceous glands, eccrine sweat glands and the infundibular epithelium of hair follicles. Expression in atopic dermatitis and psoriasis was found to extend to several layers of the stratum spinosum. In wound healing, cystatin M/E was not found in the edge of migrating keratinocytes, but it was strongly expressed in the suprabasal layers of the neo-epidermis. In epidermal neoplasias cystatin M/E expression was only found in differentiated cells and keratinized cell nests.

CONCLUSIONS

Inflammation causes cystatin M/E to be expressed in the spinous cell layers where it colocalizes with transglutaminase for which it serves as a substrate. Speculatively, increased expression of cystatin M/E is compatible with a role in controlling increased levels of cysteine proteinases during inflammation and infection. Cystatin M/E expression in neoplastic epidermis is confined to well-differentiated cells and as such does not discriminate between benign and (pre)malignant epidermal neoplasias.

Predictive value of amniotic fluid cystatin C levels for the early identification of fetuses with obstructive uropathies

OBJECTIVE

To compare the diagnostic accuracy of cystatin C with that of creatinine in discriminating renal function in fetuses without ultrasononographic evidence of renal malformations from those with obstructive uropathies.

DESIGN

Prospective, observational cohort study.

SETTING

Prenatal morphologic and functional evaluation of fetal obstructive uropathies throughout pregnancy.

POPULATION

A total of 96 healthy pregnant women at different stages of pregnancy, without any pregnancy-related maternal disease. Eighty-one pregnant women without clinical and ultrasonographic evidence of any fetal anomaly, confirmed at birth, were defined as controls; 15 pregnant women with various fetal obstructive uropathies, evidenced by repeated ultrasound examinations and confirmed at birth, were defined as cases.

METHODS

Creatinine was measured by a kinetic Jaffe picric acid method and cystatin C by a nephelometric immunoassay. Variables were analysed by applying conventional statistical tests; the non-parametric receiver operating curves (ROC) analysis was used to evaluate the diagnostic efficiencies of the biochemical markers.

MAIN OUTCOME MEASURES

Incidence of confirmed, diagnosed, neonatal obstructive uropathy by measuring baseline levels of cystatin C and creatinine in amniotic fluid.

RESULTS

Baseline levels of cystatin C in amniotic fluid were significantly higher (P = 0.0015) among cases than in controls with comparable gestational age; no significant difference was found for creatinine levels (P = n.s.). The maximum diagnostic accuracy of serum cystatin C in discriminating controls from fetal uropathies was 96%, while that of creatinine was 62%.

CONCLUSION

Cystatin C may be considered a sensitivebiochemical marker for the early identification of fetuses with obstructive uropathies.

Prediction of pelvic lymph node metastasis by the ratio of cathepsin B to stefin A in patients with prostate carcinoma

BACKGROUND

Pathologic grade and/or histologic score, extraprostatic extension indicated by invasion of the prostatic capsule, margin, and/or seminal vesicles by prostate cancer cells, serum total prostate-specific antigen (PSA), free PSA, complexed PSA levels and/or their ratios, regional pelvic lymph node metastases, and clinical staging have been used to diagnose and monitor the treatment of prostate carcinoma (PC) patients. The Gleason grading system is also used to grade/score a patient's stage of disease, with lower to higher scores indicating progression of PC. However, Gleason's system cannot be used to distinguish biologically aggressive PCs within a single Gleason score. Our objective was to identify subpopulations (or clones) of aggressive prostate cancers within an individual Gleason score by utilizing biological molecule(s) that also facilitate cancer cell invasion to prostatic stroma and metastasis to the lymph nodes.

MATERIALS AND METHODS

Specimens were collected from 97 patients with PC and from 8 patients with benign prostatic hyperplasia. These patients had not been treated with hormonal and/or chemotherapeutic agents before undergoing a prostatectomy at the Minneapolis Veterans Affairs Medical Center. Formalin-fixed, paraffin or paraplast-embedded prostate tissue sections were stained with hematoxylin and eosin for pathologic diagnosis and adjacent sections were stained for for immunohistochemical study. We also collected data on age, race, extraprostatic extension, margin status, seminal vesicle, and lymph node invasion by cancer cells, clinical stage at prostatectomy, and mortality/survival data, including the available presurgery and postsurgery serum total PSA and prostatic acid phosphatase concentrations in patients. Immunohistochemical localization of mouse or rabbit anti-cathepsin B (CB) antibody IgG and mouse antihuman stefin (cystatin) A IgG was quantified using a computer-based image analysis system equipped with Metamorph software.

RESULTS

CB and stefin A identified aggressive and less aggressive clones of PCs within an individual Gleason score. Tumors with a Gleason Score of 6 that are similar histologically and morphologically were heterogeneous with respect to the ratios of CB to stefin A (CB > stefin A, CB = stefin A, and CB < stefin A). We also found a significant positive association (P = 0.0066) between ratios of CB and stefin A (CB > stefin A) and the incidence of pelvic lymph node metastases, but not with ratios of CB less than stefin A and/or ratios of CB equal to stefin A. Patients with Gleason 7 PCs had a higher incidence of positive lymph nodes than those with Gleason Score 6 tumors. Our data indicated that mortality rates increased in patients when the ratios of CB were greater than stefin A.

CONCLUSIONS

PC within an individual Gleason score is a heterogeneous tumor that contains clones or subpopulations of aggressive and less aggressive tumors that can be defined by the ratios of CB to stefin A. PC with an aggressive clone can be identified when the ratio of CB is greater than that of stefin A. Less aggressive clones are identified when the ratio of CB is less than that of stefin A or when the ratio of CB is equal to that of stefin A. The ratios of CB to stefin A can be used in the differential diagnosis and treatment of patients with PC. This is the first report to identify phenotypes of aggressive and less aggressive PCs within a Gleason score.

Hypoxia and reoxygenation of brain microvascular smooth muscle cells in vitro: cellular responses and expression of cerebral amyloid angiopathy-associated proteins

Hypoxia is known to cause complex cascades of physiological, biochemical, and morphological changes in the brain. Cerebral microvascular smooth muscle cell (MV-SMC) damage may occur following hypoxic conditions and lead to SMC dysfunction. However, little is known about the exact cellular and molecular responses of these cells to hypoxia. To partly address these questions, MV-SMC were isolated from human brain, cultured and placed in conditions of ambient hypoxia (H) and hypoxia followed by reoxygenation (H/R). Cell morphology, proliferation, and the expression of amyloid precursor protein (APP) and cystatin C peptide were investigated and compared (after induction of hypoxia) between cerebral MV- and human aortic SMC. Our results show that MV-SMC proliferation was inhibited after 48 h of hypoxia and H/R, whereas aortic SMC proliferation was stimulated after 48 h of hypoxia and H/R. Hypoxia and H/R induced an increase of intracellular APP and cystatin C expression in both types of SMC, though the effect of H and H/R on APP upregulation was quantitatively more robust in MV-SMC than aortic SMC. Patterns of hypoxia-induced APP upregulation in SMC differed significantly from those found in cultured neuronal cells (PC12, NT2). These results suggest that hypoxia and H/R-induced APP and cystatin C upregulation appear to occur independently of the inhibition of cerebral MV-SMC proliferation. Overexpression of APP and cystatin C in response to hypoxia may thus represent an initiating event in the pathogenesis of amyloid angiopathy, or mediate progression of this microvascular lesion.

[Cystatin C and small molecular mass proteins as new markers for determination of glomerular filtration rate]

nema

Cystatin C of pleural effusion as a novel diagnostic aid in pleural diseases of different aetiologies

There has been considerable recent interest in the potential use of serum cystatin C as a diagnostic tool. Here we examined the hypothesis that the cystatin C level in the pleural effusion can differ from the corresponding serum level. We evacuated pleural effusion fluids from 47 patients by thoracentesis. Cystatin C, beta(2)-microglobulin, inorganic phosphate, creatinine and total protein were quantified in both pleural effusion fluids and corresponding sera. We determined cystatin C levels in pleural effusions and calculated the ratio of cystatin C levels in serum and effusion, to discriminate between effusions caused by severe renal impairment and other types of effusion. Extremely high concentrations of cystatin C in serum/effusion pairs were only measured in patients with renal failure (6.0 +/- 0.8/6.0 +/- 0.8 mg/l, means +/- S.D., n=11). A clearly defined region was found to correspond to pleural effusion caused by renal failure (r=0.954). The quantification of cystatin C in the effusion was justified by the discovery that there were some patients with a high serum cystatin C level but a low effusion concentration, or a low serum cystatin C but a high effusion concentration, indicating causes other than renal failure. In conclusion, the pilot data indicate a relationship between the cystatin C concentration in pleural fluid and the underlying disease. Thus cystatin C levels in pleural effusion and serum may be a valuable criterion for the differential diagnosis of pleural diseases of different aetiologies.

Analysis of native proteins from biological fluids by biomolecular interaction analysis mass spectrometry (BIA/MS): exploring the limit of detection, identification of non-specific binding and detection of multi-protein complexes

Biomolecular interaction analysis mass spectrometry (BIA/MS) is a two-dimensional analytical technique that quantitatively and qualitatively detects analytes of interests. In the first dimension, surface plasmon resonance (SPR) is utilized for detection of biomolecules in their native environment. Because SPR detection is non-destructive, analyte(s) retained on the SPR-active sensor surface can be analyzed in a second dimension using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The qualitative nature of the MALDI-TOF MS analysis complements the quantitative character of SPR sensing and overcomes the shortcomings of the SPR detection stemming from the inability to differentiate and characterize multi-protein complexes and non-specific binding. In this work, the benefit of performing MS analysis following SPR sensing is established. Retrieval and detection of four markers present in biological fluids (cystatin C, beta-2-microglobulin, urinary protein 1 and retinol binding protein) was explored to demonstrate the effectiveness of BIA/MS in simultaneous detection of clinically related biomarkers and delineation of non-specific binding. Furthermore, the BIA/MS limit of detection at very low SPR responses was investigated. Finally, detection of in-vivo assembled protein complexes was achieved for the first time using BIA/MS.

Expression of cathepsin B and cystatin C in human breast cancer

Cathepsin B, which was originally found to be a lysosomal cysteine protease, is also an important matrix protease. In this study, we investigated the expression of cathepsin B and cystatin C, the strongest inhibitor of cathepsin B, and measured the relative amounts of each in human breast cancer tissues. Cystatin C expression relative to cathepsin B expression was found to be decreased. This finding could be associated with the looseness of cancerous interstitial tissue, which might play a role in cancer invasion and metastasis. This report documents the first simultaneous investigation of cathepsin B and cystatin C in breast cancer tissues.

Increased cystatin C in astrocytes of transgenic mice expressing the K670N-M671L mutation of the amyloid precursor protein and deposition in brain amyloid plaques

Cystatin C is an essential secretory cofactor for neurogenesis with potent protease inhibitor activities. Polymorphisms of cystatin C are genetically associated with Alzheimer's disease (AD), and the L68Q mutation causes hereditary cerebral hemorrhage with amyloidosis of the Icelandic type, in which cystatin C and beta-amyloid are colocalized in cortical blood vessels. To determine whether cystatin C and beta-amyloid also colocalize in brain amyloid plaques, we analyzed transgenic mice expressing the Swedish APP (SweAPP) mutation. We found high levels of cystatin C in astrocytes surrounding beta-amyloid plaques, and discrete layers of cystatin C attached to amyloid plaque cores covered by a layer of beta-amyloid. In addition, cystatin C accumulated in reactive astrocytes throughout the brain, independently of, and before the onset of, amyloid plaque formation. These results show that expression of SweAPP is associated with increased cystatin C in reactive astrocytes, and they suggest an early role of cystatin C in appositional amyloid plaque growth.

Changes in chicken egg white cystatin concentration and isoforms during embryogenesis

1. A higher concentration of cystatin, measured using the ELISA technique, was found in whites from unfertilised than fertilised eggs. 2. Up to day 8 of embryogenesis a decrease in cystatin concentration was observed, then at d 10 the concentration rose reaching the maximal value at d 14. 3. Immunoblot analyses showed both phosphorylated and nonphosphorylated isoforms of chicken cystatin in unfertilised egg white as well as in egg yolk and chicken serum. 4. Significantly lower immunostaining of the phosphorylated form after the 4th d of embryogenesis in egg white suggests its preferential transport into the yolk sac.

Identification and localization of retinal cystatin C

PURPOSE

Cystatin C is a mammalian cysteine protease inhibitor, synthesized in various amounts by many kinds of cells and appearing in most body fluids. There are reports that it may be synthesized in the mammalian retina and that a cysteine protease inhibitor may influence the degradation of photoreceptor outer segment proteins. In the current study cystatin C was identified, quantitated, and localized in mouse, rat, and human retinas.

METHODS

Enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR), DNA sequencing, Western blot analysis, and immunohistochemistry have been used on mouse, rat, and human retinas (pigment epithelium included).

RESULTS

Cystatin C is present in high concentrations in the normal adult rat retina, as it is throughout its postnatal development. Its concentration increases to a peak at the time when rat pups open their eyes and then remains at a high level. It is mainly localized to the pigment epithelium, but also to some few neurons of varying types in the inner retina. Cystatin C is similarly expressed in normal mouse and human retinas.

CONCLUSIONS

Cystatin C was identified and the localization described in the retinas of rat, mouse, and human using several techniques. Cystatin C is known to efficiently inactivate certain cysteine proteases. One of them, cathepsin S, is present in the retinal pigment epithelium and affects the proteolytic processing by cathepsin D of diurnally shed photoreceptor outer segments. Hypothetically, it appears possible that retinal cystatin C, given its localization to the pigment epithelium and its ability to inhibit cathepsin S, could be involved in the regulation of photoreceptor degradation.

Diagnostic applications of cystatin C

Cysteine proteases are proteolytic enzymes involved in many pathological processes and found in the lysosomes of cells; examples include the cathepsins B, H and L. The role of cysteine proteases is crucial in normal cellular metabolism, being fundamental to intracellular protein turnover, degradation of collagen, and cleaving of precursor proteins. Cysteine protease inhibitors, of which the cystatin superfamily are one example, constitute the final regulatory step in the control of cysteine proteases. Currently, cystatin C is the most frequently investigated family member and is involved in processes such as tumour invasion and metastasis, inflammatory processes and some neurological diseases. In such diseases the emphasis is placed on the fine balance and regulation of both the cysteine proteases and their inhibitors, with an imbalance resulting in a pathological state. In addition, the constant serum concentration of cystatin C means it has possible application as a replacement for creatinine in the measurement of glomerular filtration rate. To date, several assays have been developed and studies show a promising future for its use in the medical laboratory, and not just as a research tool. This review of cystatin C includes a brief history of its discovery and characterisation, provides a guide to some of the processes in which its role is fundamental, and highlights developments in its use as a clinical biomarker in the disease processes discussed.

The cerebral hemorrhage-producing cystatin C variant (L68Q) in extracellular fluids

A variant of the normal extracellular cysteine protease inhibitor cystatin C (L68Q-cystatin C), is the amyloid precursor in hereditary cystatin C amyloid angiopathy (HCCAA). It has been suggested that the mutation causes cellular entrapment of L68Q-cystatin C in vivo and that the variant protein is not secreted to extracellular fluids. In order to test this hypothesis, we used matrix-assisted laser desorption ionization time-of-flight mass spectrometry in an effort to demonstrate the presence of L68Q- along with wildtype cystatin C in plasma and cerebrospinal fluid (CSF) of HCCAA-patients. Plasma from all five investigated HCCAA-patients contained both L68Q- and wildtype cystatin C. The presence of approximately equal amounts of cystatin C dimers and monomers was demonstrated in plasma from HCCAA-patients, whereas only monomers could be found in normal plasma. L68Q-wildtype-cystatin C heterodimers seem to be present in the dimeric cystatin C population. CSF from six HCCAA-patients also contained cystatin C-dimers and monomers, but the dimeric fraction was minute. CSF from control patients did not contain dimeric cystatin C. These results suggest that the milieu of L68Q-cystatin C is important for its stability and dimerization status and that certain milieus might hinder its further development into oligomers, amyloid fibrils and other precipitating aggregates.

Improved immunoturbidimetric assay for cystatin C

An immunoturbidimetric assay for cystatin C was optimized with respect to assay imprecision. After investigating the optimum pH, polyethylene glycol concentration and specimen volume, two modifications were introduced: an increase in specimen volume to 25 microL; and an extension of the pre-incubation period to 240 s. These modifications produced an assay with between-batch imprecision (coefficient of variation, n = 10 or 11) ranging from 3-9% at 0.72 mg/L to 1.3% at 5.29 mg/L. The assay was susceptible to interference from lipaemia and haemolysis but not bilirubinaemia in both the original and modified protocol. Extending the pre-incubation to 240 s improved tolerance to common interferences and retained assay applicability in the routine clinical setting.

Tissue distribution of bovine cystatin C analysed by in situ hybridisation

Cysteine proteinase inhibitors of the cystatin superfamily have been identified in many living organisms. However, knowledge of the tissue distribution of such inhibitors is limited. To elucidate this distribution in mammals, we have investigated the expression of the gene for cystatin C, belonging to cystatin family II, in several bovine tissues. In situ hybridisation with a digoxigenin-labelled cRNA probe demonstrated a high concentration of bovine cystatin C mRNA in the secretory epithelial cells of the choroid plexus, and also intense staining in cells of lymphoid tissue and in Sertoli cells. Cystatin C mRNA was also present in scattered neurons and glial cells throughout the cerebrum and the cerebellum. In the submandibular gland, specific mRNA was found mainly in striated intralobular ducts and interlobular ducts. The expression of cystatin C in brain tissue is of particular interest, as the inhibitor appears to be involved in certain neurological diseases. The main production of cystatin C within the brain is believed to be by astrocytes. However, this work shows that also neurons from young, normal individuals express cystatin C.

IgM and IgG cystatin capture enzyme linked immunosorbent assays: a tool for serodiagnosis and assessment of cure of acute fascioliasis after triclabendazole (TCZ; Fasinex) therapy

This study included 71 individuals: 25 patients with confirmed acute fascioliasis, 9 patients with suspected fascioliasis, 27 patients with parasitic infections other than fascioliasis and 10 normal controls. Patients with fascioliasis were treated with TCZ as a single dose and followed up 1 and 4 months after therapy. The results showed that both IgM and IgG cystatin capture ELISAs had very high sensitivity and specificity of 100%. They were also able to diagnose early fascioliasis even before indirect haemagglutination test (IHAT) became positive. Within 4 months after treatment, only 20 patients (80%) with fascioliasis were cured as evidenced clinically, by normal eosinophil count and negative IHAT. After the first month of treatment, IgM and IgG cystatin capture ELISAs became negative in 16.6% and 83.3% of the cured cases respectively, reaching 95% for both assays after 4 months. They remained positive in 5 cases (20%) not responding to treatment.

Sialochemical markers of salivary gland involvement with Sjögren's syndrome secondary to rheumatoid arthritis and primary biliary cirrhosis

Sjögren's syndrome is an autoimmune condition affecting the lacrimal and salivary glands and can be associated with rheumatoid arthritis and primary biliary cirrhosis. Parotid salivas collected from patients and normal controls were analysed for lactoferrin, IgA and beta2-microglobulin (measured by ELISA), and cystatin (measured by a enzyme inhibition assay). Output data provided less variable means, whilst expressing results as a proportion of the total protein provided greater specificity as markers for Sjögren's syndrome. Levels of specificity for IgA, lactoferrin and beta2-microglobulin were all high (100, 95 and 100%, respectively). Sensitivity levels of these markers (but not cystatin) tended to be similar for Sjögren's syndrome secondary to primary biliary cirrhosis (IgA, 25%; lactoferrin, 63%; and beta2-microglobulin, 50%), compared to Sjögren's syndrome secondary to connective tissue diseases such as rheumatoid arthritis (IgA, 50%; lactoferrin, 86%; and beta2-microglobulin; 38%).

Synovial giant cells in rheumatoid arthritis: expression of cystatin C, but not of cathepsin B

This study was designed to investigate the expression of the matrix degrading proteinase cathepsin B and its endogenous inhibitor cystatin C in rheumatoid arthritis (RA) with special regard to multinucleated synovial giant cells (SGC). We applied an immunohistochemical double-labeling technique. SGC strongly expressed cystatin C and CD68, but were negative for cathepsin B. This staining pattern occurred in osteoclasts as well. Our findings support the idea that in RA matrix destruction by cathepsin B is not mediated by SGC or osteoclasts, but by mononuclear synoviocytes.