C4d deposits mark sites of meniscal tissue disintegration

Osteoarthritis and the Complement Cascade

Accumulating evidence demonstrates that complement activation is involved in the pathogenesis of osteoarthritis (OA). However, the intimate complement regulation and cross talk with other signaling pathways in joint-associated tissues remain incompletely understood. Recent insights are summarized and discussed here, to put together a more comprehensive picture of complement involvement in OA pathogenesis. Complement is regulated by several catabolic and inflammatory mediators playing a key role in OA. It seems to be involved in many processes observed during OA development and progression, such as extracellular cartilage matrix (ECM) degradation, chondrocyte and synoviocyte inflammatory responses, cell lysis, synovitis, disbalanced bone remodeling, osteophyte formation, and stem cell recruitment, as well as cartilage angiogenesis. In reverse, complement can be activated by various ECM components and their cleavage products, which are released during OA-associated cartilage degradation. There are, however, some other cartilage ECM components that can inhibit complement, underlining the diverse effects of ECM on the complement activation. It is hypothesized that complement might also be directly activated by mechanical stress, thereby contributing to OA. The question arises whether keeping the complement activation in balance could represent a future therapeutic strategy in OA treatment and in the prevention of its progression.

A Porcine Animal Model for Early Meniscal Degeneration - Analysis of Histology, Gene Expression and Magnetic Resonance Imaging Six Months after Resection of the Anterior Cruciate Ligament

BACKGROUND/OBJECTIVE

The menisci of the mammalian knee joint balance the incongruence between femoral condyle and tibial plateau and thus menisci absorb and distribute high loads. Degeneration processes of the menisci lead to pain syndromes in the knee joint. The origin of such degenerative processes on meniscal tissue is rarely understood and may be described best as an imbalance of anabolic and catabolic metabolism. A standardized animal model of meniscal degeneration is needed for further studies. The aim of the current study was to develop a porcine animal model with early meniscal degeneration.

MATERIAL AND METHODS

Resection of the anterior cruciate ligament (ACLR) was performed on the left knee joints of eight Göttingen minipigs. A sham operation was carried out on the right knee joint. The grade of degeneration was determined 26 weeks after the operation using histology and magnetic resonance imaging (MRI). Furthermore, the expression of 14 genes which code for extracellular matrix proteins, catabolic matrix metalloproteinases and inflammation mediators were analyzed.

RESULTS

Degenerative changes were detected by a histological analysis of the medial meniscus after ACLR. These changes were not detected by MRI. In terms of their gene expression profile, these degenerated medial menisci showed a significantly increased expression of COL1A1.

CONCLUSION

This paper describes a new animal model for early secondary meniscal degeneration in the Göttingen minipig. Histopathological evidence of the degenerative changes could be described. This early degenerative changes could not be seen by NMR imaging.

Comparative immunohistochemical evaluation of the zonal distribution of extracellular matrix and inflammation markers in human meniscus in osteoarthritis and rheumatoid arthritis

The purpose of our study was to analyze the distribution of the major extracellular matrix glycosaminoglycan hyaluronan (HA), its receptor CD44 and cells which influence (re)modeling of the extracellular matrix (T- and B-cells, macrophages, endothelial cells) in menisci obtained from patients suffering from rheumatoid arthritis or osteoarthritis in order to analyze whether these markers could be useful to differentiate between both arthropathies. Human menisci were sampled from patients undergoing total knee arthroplasty. Histological staining (H&E, PAS/Alcian Blue for neutral and charged carbohydrate residues) and (immuno)histochemistry were performed for detection of HA, CD44, sphingosine-1-phosphate receptor 1 (EDG-1) as a marker for endothelial cells, CD3 as a marker for T-cells, CD20 as a marker for B-cells and CD68 as a marker for macrophages. The extracellular matrix in the vascularized zone showed higher amounts of HA as well as acid carbohydrate residues in comparison to the poorly vascularized zones of the meniscus in both disease entities. EDG-1 positive endothelial cells were present in all zones, with fewer cells being detected in the inner zones of the rheumatoid menisci than in the osteoarthritic ones. Macrophages, T- and B-cells as well as CD44-positive cells were more prominent in the vascularized zone of the meniscus than in the poorly vascularized central zone. The distribution patterns of the extracellular matrix components as well as the CD44-positive cells and the inflammation markers in the peripheral zone resembled the distribution in synovial tissue, indicating that both synovia and meniscus were involved in pathological changes in osteoarthritis and rheumatoid arthritis.

IN CONCLUSION

the distribution of extracellular glycoconjugates and of cells modulating their synthesis showed similar results in both arthropathies, not enabling a differentiation between rheumatoid arthritis and osteoarthritis but underlining the role of these markers in inflammation and degradation in human meniscus.

[Histopathological degeneration score of fibrous cartilage. Low- and high-grade meniscal degeneration]

Although histopathology of meniscal degeneration plays an important role, no criteria to assess severity of the degeneration are available to date. Our aim was to create a histopathological scoring system for meniscal degeneration with good interobserver variability, taking matrix degradation and cellularity in meniscal tissue into consideration. Degeneration is classified as follows: grade 1 (low), grade 2 (intermediate), grade 3 (high). The pattern of NITEGE deposits (G1 fragment of aggrecan) was assessed immunohistochemically (n=38) and compared with the grades of degeneration. In 48% of the patients with grade 2 or 3 degeneration extracellular NITEGE deposits (specificity 100%) were found, whereas grade 1 patients showed no deposits. Extracellular NITEGE deposits correlated positively with the grade of degeneration. In all, 30 cases (10 per grade) were assessed by three pathologists (A, B, C). Grading conformity was 70% for grade 1, 66% for grade 2 and 100% for grade 3. Cohen's Kappa coefficient was 0.6--0.7 between pairs of observers. Combining grade 1 and 2 to low-grade degeneration, compared to a grade-3 high-grade degeneration achieved Kappa coefficients of between 0.93 and 1.0. This reproducible degeneration score for fibrous cartilage could form the basis for the standardized assessment of meniscal degeneration.

[Meniscal degeneration score and NITEGE expression : immunohistochemical detection of NITEGE in advanced meniscal degeneration]

BACKGROUND

Meniscal degeneration (MD) is a structural change of fibrous cartilage that is common in orthopaedic diagnostics and relevant for health insurance matters. So far, there has been neither a standardised scoring system nor an immunohistochemical marker for MD.

MATERIAL AND METHOD

In this retrospective trial, the meniscal tissue of 60 patients was assessed immunohistochemically for NITEGE (G1 fragment of the proteoglycan aggrecan) expression. NITEGE expression was correlated with defined grades of MD: little (grade 0/1), medium (grade 2), or severe (grade 3).

RESULTS

Detection of extracellular NITEGE deposits in grade 2 or 3 MD had a positive predictive value and specificity of 100%, whereas no deposits were found in grade 0/1 MD. Sensitivity in advanced MD was 55%. Detection of extracellular NITEGE correlated positively with the grade of degeneration, as did patient age and the grade of degeneration. The patient age of those with grade 0/1 MD was significantly lower than for grade 3 (p<0.0001).

CONCLUSION

The thoroughly defined degeneration score (grade 1 - grade 3 MD) is suitable to assess the severity of degeneration. Extracellular NITEGE deposits can be regarded as an immunohistochemical marker for advanced (grades 2 and 3) MD.

Colocalization of C4d deposits/CD68+ macrophages in rheumatoid nodule and granuloma annulare: immunohistochemical evidence of a complement-mediated mechanism in fibrinoid necrosis

Rheumatoid nodule (RN) represents a palisading granuloma with central fibrinoid necrosis, which is not only a classical manifestation of rheumatoid arthritis (RA) and part of the American College of Rheumatology (ACR)-criteria, but also is its diagnostic hallmark. The pathogenesis of RN is still not fully understood. At present, only data on serum analyses indicating a complement-mediated pathogenesis in the development of RA are available. Equivalent examinations for RN have not yet been performed. Granuloma annulare (GA) represents another type of palisading granuloma. A special subtype of GA, subcutaneous GA (SGA), is an important differential diagnosis to RN. Therefore, our aim was to examine RN and SGA regarding the complement deposition (C4d) by immunohistochemical means. All RN and GA were stained by hematoxylin/eosin and different special stains. In addition, all specimens were stained immunohistochemically with antibodies against CD68. Five GA and five RN were analyzed immunohistochemically with antibodies against C4d and CD68, and evaluated using single- and doublestaining immunohistochemistry. All RN and GA displayed depositions of C4d within their central necroses and between the surrounding palisading macrophages. Most importantly, C4d/CD68 double staining was visible in the palisading macrophages next to the necroses, while macrophages in the periphery were negative for C4d but positive for CD68. The main difference between RN and GA was a quantitative phenomenon with less positively reacting macrophages in a more incomplete palisade in GA. The positive reactions of all central necroses to C4d and colocalization of CD68 and C4d suggest that a complement-mediated mechanism may be operative in the formation of fibrinoid necrosis. This mechanism may be involved in any form of "fibrinoid necrosis", since no different patterns of C4d/CD68 expression could be observed in GA. This may explain why RG/GA are not distinguishable morphologically.