Possible clearance of effete polymorphonuclear leucocytes from synovial fluid by cytophagocytic mononuclear cells: implications for pathogenesis and chronicity in inflammatory arthritis

Seasonal variation and disease distribution of cytophagocytic mononuclear cells in synovial fluid: A medical record study

Cytophagocytic mononuclear (CPM) cells, previously known as Reiter's cells, are macrophages containing apoptotic polymorphonuclear leucocytes. Although they can be found in synovial fluid (SF) from different arthropathies, their role remains unclear. This study was performed to determine the frequency and disease distribution of CPM cells in SF in a large cohort of patients with rheumatic diseases over a 12-year period. We also investigated the seasonal variation in their incidence. This record review study included the reports pertaining to SF analyses performed between January 2010 and December 2021. Data were retrieved from the charts of inpatients and outpatients at Rheumatology and Emergency Departments of Padova. The total number of SF samples containing CPM cells was 189: 69% was from patients with seronegative spondyloarthritis (SpA), thus indicating a strong association between CPM cells and SpA. SF samples containing CPM cells were predominantly inflammatory. Our analyses demonstrated a 6-month cyclical fluctuation in concentrations of CPM cells, with an increase in spring and autumn. The presence of CPM cells in SF might offer diagnostic insight into the definition of SpA. Further studies are warranted to ascertain the link between CPM cells and the apoptotic process, shedding light on the mechanisms leading to their formation.

[Synovial fluid cytodiagnosis]

Synovial fluid samples represent only a very small percentage of routine work in a cytology laboratory. However, its microscopic examination allows us to observe different types of cells, particles and structures that, due to their morphological characteristics, may provide relevant data for cytodiagnosis. We present certain aspects related to arthrocentesis, the relationship between the gross appearance of synovial fluid and certain pathological processes, as well as the different techniques for processing and staining the smears. Furthermore, we describe the main cytological findings in various pathological conditions of the synovial joints, such as infections (bacterial and fungal), non-infectious inflammatory type (osteoarthrosis, rheumatoid arthritis, connective tissue diseases) and tumoral, distinguishing between primary and metastatic, both solid and haematological neoplasms.

Evaluation of neutrophil-to-lymphocyte ratio as a marker of inflammatory response in septic arthritis

Is neutrophil-to-lymphocyte ratio high in patients with septic arthritis? Septic arthritis may lead to higher rates of morbidity or even mortality if not diagnosed on time. This study was planned to answer the question that “Could neutrophil-to-lymphocyte ratio be utilized to help to diagnose septic arthritis?” The cohort of the study consisted of 39 patients diagnosed with septic arthritis. After ruling out the patients who did not meet the research’s inclusion criteria, the data of 26 patients were evaluated. The control group was collected from healthy volunteers who were admitted to the internal medicine outpatient clinic for a routine medical checkup at the same period (n = 26). Complete blood count (CBC) parameters, C-reactive protein, erythrocyte sedimentation rate, and neutrophil-to-lymphocyte ratios of the septic arthritis and control groups were compared statistically. In comparison, neutrophil-to-lymphocyte ratios of the septic arthritis group were significantly higher than the control group. In conclusion, neutrophil-to-lymphocyte ratio can be utilized in the emergency department or in outpatient clinics to support the diagnosis of septic arthritis.

Light and electron microscopic features of synovium in patients with psoriatic arthritis

INTRODUCTION

Few ultrastructural studies have been reported in psoriatic arthritis (PsA). The authors report a series of synovial biopsies with emphasis on patients with early disease to look for distinctive light (LM) and electron microscopic (EM) features of possible importance.

METHODS

The authors examined synovial biopsies obtained primarily by needle biopsy from 13 PsA patients using LM and/or EM. Sections from 12 patients were evaluated by LM for vascularity, synovial lining thickness, fibrin deposition, and inflammation via a semi-quantitative scale. Nine EM specimens were descriptively analyzed. Clinical, synovial fluid (SF), and radiographic characteristics were recorded.

RESULTS

Patients were mostly male, with mean disease duration before biopsy of 2.19 ± 2.60 years; 7 patients had arthritis for less than 1 year. All patients had peripheral arthritis, 2 had axial involvement. SFs disclosed predominance of polymorphonuclear leukocytes. LM demonstrated proliferation of synovial lining cells, lymphocyte and plasma cell infiltration, as well as dramatic clusters of small vessels in the superficial synovium. EMs showed more detailed vascular changes, including small, subendothelial, electron-dense deposits and scattered microparticles in vessel lumens and walls.

CONCLUSIONS

Prominent vascularity is confirmed as an important feature of some PsA. Vascular changes and other features, including the first EM demonstration of microparticles in PsA (identified as potent factors in other inflammatory joint diseases), are potential targets for therapy.

The melanocortin agonist AP214 exerts anti-inflammatory and proresolving properties

Synthetic and natural melanocortin (MC) peptides afford inhibitory properties in inflammation and tissue injury, but characterization of receptor involvement is still elusive. We used the agonist AP214 to test MC-dependent anti-inflammatory effects. In zymosan peritonitis, treatment of mice with AP214 (400 to 800 μg/kg) inhibited cell infiltration, an effect retained in MC receptor type 1, or MC(1), mutant mice but lost in MC(3) null mice. In vitro, cytokine release from zymosan-stimulated macrophages was affected by AP214, with approximately 80%, 30%, and 40% reduction in IL-1β, tumor necrosis factor-α, and IL-6, respectively. Inhibition of IL-1β release was retained in MC(1) mutant cells but was lost in MC(3) null cells. Furthermore, AP214 augmented uptake of zymosan particles and human apoptotic neutrophils by wild-type macrophages: this proresolving property was lost in MC(3) null macrophages. AP214 displayed its pro-efferocytotic effect also in vivo. Finally, in a model of inflammatory arthritis, AP214 evoked significant reductions in the clinical score. These results indicate that AP214 elicits anti-inflammatory responses, with a preferential effect on IL-1β release. Furthermore, we describe for the first time a positive modulation of an MC agonist on the process of efferocytosis. In all cases, endogenous MC(3) is the receptor that mediates these novel properties of AP214. These findings might clarify the tissue-protective properties of AP214 in clinical settings and may open further development for novel MC agonists.

Effects of laser on the synovial fluid in the inflammatory process of the knee joint of the rabbit

OBJECTIVE

The purpose of this study was to evaluate the effects of low-level laser (LLL) energy on the clinical signs of inflammation and the cellular composition of synovial fluid (SF) in the inflamed knee of the rabbit.

BACKGROUND DATA

There are few findings related to the effects of LLL on SF in inflammatory processes and there is little knowledge about the optimal parameters for reducing joint inflammation.

MATERIALS AND METHODS

Inflammation in the right knee of 36 rabbits was induced by intracapsular injection (0.2 mL) of Terebinthina commun (Tc). The animals were randomly assigned to three groups: acute experimental group (AEG), chronic experimental group (CEG), and control group (CG), which only received Tc. Each group was divided in two subgroups of six animals each. The AEG and CEG groups began to receive laser treatment 2 and 5 d after the induction of inflammation, respectively. Laser irradiation at a wavelength of 830 nm, power output of 77 mW, and power density of 27.5 W/cm(2) was applied daily for 7 d for either 0.12 sec or 0.32 sec, resulting in doses of 3.4 J/cm(2) and 8 J/cm(2), respectively. Body mass, joint perimeter, joint temperature, and the morphology of the SF were analyzed.

RESULTS

There was no statistically significant differences between groups in the body mass, joint perimeter, and SF morphology.

CONCLUSION

Laser irradiation with the selected parameters produced only a few subtle differences in the inflammatory signs and the SF. The lack of effects may have been due to the short irradiation time.

Gout: Update on Some Pathogenic and Clinical Aspects

Pathogenesis of gout inflammation remains unknown, but recent advances have been made with respect to initiation, amplification, and self-limitation. Direct crystal-cell membrane contact leads to cell activation, involving membrane-associated molecules. Resolution of acute gout inflammation is a mechanism that is controlled by monocyte-macrophage switch, which results in the loss of cytokine production capability and, conversely, the ability to produce anti-inflammatory molecules. MRI and ultrasound findings provide preliminary data that are not yet used in clinical trials. Diagnosis and management recommendations are missing, but this gap will be filled soon with the upcoming European League Against Rheumatism Task Force's recommendations on gout.

Cell synthesis, proliferation and apoptosis in human dental periapical lesions analysed by in situ hybridisation and immunohistochemistry

OBJECTIVE

The role of structural and host defensive cells in periapical lesions has been assessed previously by morphometric and immunohistochemical studies. The aim of this study was to investigate the function of peri- apical cells by employing molecular techniques to estimate the cell synthetic activity, proliferation and apoptosis in these lesions. We specifically sought answers to the following questions. Which cells of the periapical lesions are quiescent or actively synthesising proteins? Do immune cells proliferate in this region in the same way as epithelial cells proliferate? Furthermore do cells in peri- apical lesions undergo apoptosis, and if so which cells exhibit this programmed cell death?

MATERIALS

Twenty-five periapical tissue samples (15 granulomas and 10 radicular cysts) were assessed. Poly-adenosine (poly (A)) RNA and ribosomal RNA (rRNA) bearing cells in formalin-fixed/paraffin-embedded peri- apical tissues were analysed by in situ hybridization (ISH) using digoxigenin-labelled oligo d (T) and 28S rRNA probes respectively in order to estimate cell synthetic activity. Furthermore, S-phase proliferating and cycling cells were examined by ISH using a histone probe and Ki-67 immunostaining so as to assess cellular proliferation. Mononuclear cells were further differentiated by immunohistochemistry (IHC) as T cells, B cells and macrophages. Apoptotic cells were determined by in situ end-labelling methodology for detecting fragmented DNA.

RESULTS

Poly (A) RNA (mostly messenger RNA) and 28S rRNA-expressing cells were detected in all samples. Plasma cells exhibited strongest staining for the two probes, with slight to moderate staining found in the epithelium, fibroblasts, macrophages, endothelial cells and lymphocytes, whereas almost all polymorphonuclear leucocytes (PMN) were negative for these probes. A few histone mRNA-expressing cells were detected in basal and suprabasal epithelial cells and mononuclear cells in 15/25 cases but their reactivity was weak. Ki-67 positive cells were found in all samples and their numbers were generally higher than histone mRNA positive cells. Apo- ptotic cells were detected in 23/25 cases and the majority of apoptotic cells were PMN which were engulfed by large cytophagocytic macrophages.

CONCLUSION

This study indicates that in dental periapical lesions, apoptosis occurs predominantly in PMN. It is evident that most cells apart from PMN are exhibiting synthetic activity but only epithelial cells undergo proliferation which implies that immune cells must proliferate at distant lymph nodes and travel to the periapical lesion rather than proliferating within the lesion. These results suggest considerable advantages in estimating gene expression within cells in addition to the immunohistochemical detection of cells to determine cell activity at inflamed sites. Clearly, functional cell synthetic activity, resolution and clearance systems operate in peri- apical cystic and granuloma lesions.

Regulation of Macrophage Phagocytosis of Apoptotic Cells by cAMP

Regulation of macrophage capacity to remove apoptotic cells may control the balance of apoptotic and necrotic leukocytes at inflamed foci and the extent of leukocyte-mediated tissue damage. Although the molecules involved in the phagocytic process are beginning to be defined, little is known about the underlying regulatory and signaling mechanisms controlling this process. In this paper, we have investigated the effects of treatment of human monocyte-derived macrophages with PGs and other agents that elevate intracellular cAMP on phagocytosis. PGE2 and PGD2 specifically reduced the proportion of macrophages that phagocytosed apoptotic cells. Similar results were obtained with the membrane-permeable cAMP analogues dibutyryl-cAMP and 8-bromo-cAMP but not with the cGMP analogue dibutyryl-GMP. Consistent with the observation that phagocytosis was inhibited by cAMP elevation, treatment of monocyte-derived macrophages with PGE2 resulted in rapid, transient increase in levels of intracellular cAMP. These effects were not due to nonspecific inhibition of monocyte-derived macrophage phagocytosis given that ingestion of Ig-opsonized erythrocytes was unaffected. Elevation of cAMP induced morphologic alterations indicative of changes in the adhesive status of the macrophage, including cell rounding and disassembly of structures that represent points of contact with substrate containing actin and talin. These results strongly suggest that rapid activation of cAMP signaling pathways by inflammatory mediators regulates processes that limit tissue injury and that modulation of cAMP levels represents an additional therapeutic target in the control of resolution of inflammation.

From stem cells to lymphocytes: biology and transplantation

We review the development of the hematopoietic system, focusing on the transition from hematopoietic stem cells (HSCs) to T cells. This includes the isolation of HSCs, and recent progress in understanding their ontogeny, homing properties, and differentiation. HSC transplantation is reviewed, including the kinetics of reconstitution, engraftment across histocompatibility barriers, the facilitation of allogeneic engraftment, and the mechanisms of graft rejection. We describe progress in understanding T-cell development in the bone marrow and thymus as well as the establishment of lymph nodes. Finally, the role of bcl-2 in regulating homeostasis in the hematopoietic system is discussed.

Soluble oligonucleosomal complexes in synovial fluid from inflamed joints

OBJECTIVE

To determine whether soluble oligonucleosomal DNA, typical of that released during apoptotic cell death, is present in synovial fluids from inflamed joints and, if so, whether it is present in sufficient concentrations to have pathophysiologic significance.

METHODS

Fifty synovial fluid specimens from 46 patients were studied, 41 from joints with a variety of inflammatory disorders and 9 from osteoarthritic joints. DNA from freshly collected synovial fluid was isolated and quantitated by microfluorometry, and the oligonucleosomal fraction was measured by radiolabeling, gel electrophoresis, and autoradiography. Specific immunoprecipitation with monoclonal antihistone antibody, after DNA radiolabeling in whole synovial fluid, was used to detect histone binding.

RESULTS

DNA with a typical oligonucleosomal ladder was observed in most specimens. The mean +/- SD oligonucleosomal DNA concentration was 14.1 +/- 18.5 microg/ml in synovial fluids from inflamed joints, considerably higher than that in osteoarthritic synovial fluids. Additionally, the DNA was shown to be complexed with histone, as would be expected. Control experiments were performed to show that the oligonucleosomal DNA was present in soluble form and did not arise due to in vitro artifact. The DNA concentrations were found to correlate significantly with the concentrations of synovial fluid leukocytes, most of which were neutrophils.

CONCLUSION

Synovial fluids from inflamed joints contain oligonucleosomal DNA typical of that released during apoptotic cell death. The probable source is fluid-phase neutrophils undergoing apoptotic cell death, although this was not directly demonstrated. The concentrations are sufficient to have biologic activity similar to that shown in vitro, including lymphoproliferation and stimulation of interleukin-6 secretion. A mechanism by which oligonucleosomal DNA may contribute to perpetuation of rheumatoid synovitis is proposed. If it is generalizable to other sites of inflammation, as seems probable, similar oligonucleosomal DNA release accompanying inflammation may play a pathogenetic role in other disorders, including systemic lupus erythematosus.

Inhibition of T cell apoptosis in the rheumatoid synovium

Synovial T cells in rheumatoid arthritis are highly differentiated and express a phenotype suggesting susceptibility to apoptosis (CD45RB dull, CD45RO bright, Bcl-2 low, Bax high, Fas high). However, no evidence of T cell apoptosis was found in synovial fluid from any of 28 patients studied. In contrast, synovial fluid from 10 patients with crystal arthritis showed substantial levels of T cell apoptosis. The failre of apoptosis was not an intrinsic property of rheumatoid synovial T cells, as they showed rapid spontaneous apoptosis on removal from the joint. Synovial T cells from rheumatoid arthritis and gout patients could be rescued from spontaneous apoptosis in vitro either by IL-2R gamma chain signaling cytokines (which upregulate Bcl-2 and Bcl-XL) or by interaction with synovial fibroblasts (which upregulates Bcl-xL but not Bcl-2). The phenotype of rheumatoid synovial T cells ex vivo (Bcl-2 low, Bcl-xL high) suggested a fibroblast-mediated mechanism in vivo. This was confirmed by in vitro culture of synovial T cells with fibroblasts which maintained the Bcl-xL high Bcl-2 low phenotype. Synovial T cells from gout patients were Bcl-2 low Bcl-xL low and showed clear evidence of apoptosis in vivo. Inhibition experiments suggested that an integrin-ligand interaction incorporating the Arg-Gly-Asp motif is involved in fibroblast-mediated synovial T cell survival. We propose that environmental blockade of cell death resulting from interaction with stromal cells is a major factor in the persistent T cell infiltration of chronically inflamed rheumatoid synovium.

Microscopic analysis of synovial fluid--the perfect diagnostic test?

Images

Human blood and synovial fluid neutrophils cultured in vitro undergo programmed cell death which is promoted by the addition of synovial fluid

OBJECTIVE

To assess the influence of inflammatory synovial fluid (SF) on apoptosis of joint and blood neutrophils with particular reference to levels of colony stimulating factors (CSF) contained therein.

METHODS

Neutrophils were separated from fresh synovial fluid and from peripheral blood by density gradient centrifugation. Apoptosis was assayed by light microscope morphology and DNA degradation. CSFs were assayed using bone marrow bioassay and enzyme linked immunosorbent assays for granulocyte (G-) and granulocyte macrophage (GM-) CSF. Separated neutrophils were cultured in vitro and exposed to: varying concentrations of SF in which CSF levels were measured, recombinant G-CSF and GM-CSF, and hyaluronic acid control solutions. Numbers of apoptotic neutrophils and CSF levels were also measured in fresh SF samples.

RESULTS

The addition of autologous or heterologous inflammatory SF to blood or joint cavity neutrophils cultured in vitro caused a significant dose dependent increase in the percentage of cells becoming apoptotic with time as measured morphologically and confirmed by DNA degradation. The effect bore no relationship to levels of CSF in joint fluid, despite our finding that GM-CSF produced inhibition of neutrophil apoptosis in vitro.

CONCLUSION

These data suggest that SF contains a factor or factors capable of directly or indirectly promoting neutrophil apoptosis and normally powerful enough to overcome the apoptosis inhibiting effects of cytokines such as GM-CSF at concentrations usually found in inflammatory synovial fluids.

Apoptosis in rheumatoid arthritis synovium

RA synovial tissue (ST) was studied to determine if and where apoptosis occurs in situ. Genomic DNA was extracted from 5 RA and 1 osteoarthritis ST samples. Agarose gel electrophoresis demonstrated DNA ladders characteristic for apoptosis from each tissue. In situ and labeling (ISEL) was used to identify DNA strand breaks consistent with apoptosis in frozen sections. 12 RA and 4 osteoarthritis ST were studied by ISEL and all were positive, but only 2 of 4 normal tissues were positive. The primary location of apopotic cells was the synovial lining. Some sublining cells were also positive, but lymphoid aggregate staining was conspicuously absent. Immunohistochemistry and ISEL were combined and showed that the lining cells with DNA strand breaks were mainly macrophages, although some fibroblastlike cells were also labeled. Sublining cells with fragmented DNA included macrophages and fibroblasts, but T cells in lymphoid aggregates, which expressed large amounts of bcl-2, were spared. DNA strand breaks in cultured fibroblastlike synoviocytes was assessed using ISEL. Apoptosis could be induced by actinomycin D, anti-fas antibody, IL-1, and TNF-alpha but not by IFN-gamma. Fas expression was also detected on fibroblast-like synoviocytes using flow cytometry. Therefore, DNA strand breaks occur in synovium of patients with arthritis. Cytokines regulate this process, and the cytokine profile in RA (high IL-1/TNF; low IFN-gamma) along with local oxidant injury might favor induction of apoptosis.

Autoimmune disease. A problem of defective apoptosis

Human autoimmune diseases share the common feature of an imbalance between the production and destruction of various cell types including lymphocytes (SLE), synovial cells (RA), and fibroblasts (scleroderma). Patients with SLE have increased levels of soluble Fas that inhibit proper apoptosis of lymphocytes. In animal models of autoimmune diseases, mutations of genes involved in apoptosis including Fas, Fas ligand, and the hematopoietic cell phosphatase gene have been identified. Oncogenes, including bcl-2, p53, and myc, that regulate apoptosis are also expressed abnormally. Potent inducers of apoptosis including steroids, azathioprine, cyclophosphamide, and methotrexate are the most efficacious therapies for autoimmune disease currently known. Specific therapies that induce apoptosis without incurring side effects should improve treatment of autoimmune disease.

bcl-2 inhibits apoptosis of neutrophils but not their engulfment by macrophages

Neutrophils, the most common inflammatory leukocytes, have the most limited life span of all blood cells. After they undergo apoptosis, they are recognized and engulfed by macrophages. bcl-2, a proto-oncogene rearranged and deregulated in B cell lymphomas bearing the t(14;18) translocation, is known to inhibit programmed death. bcl-2 expression is localized in early myeloid cells of the bone marrow but is absent in mature neutrophils. Transgenic mice that expressed bcl-2 in mature neutrophils showed that bcl-2 blocked neutrophil apoptosis. Despite this, homeostasis of neutrophil population is essentially unaffected. In fact, macrophage uptake of neutrophils expressing bcl-2 still occurred. This transgenic model indicates that the mechanism that triggers phagocytosis of aging neutrophils operates independently of the process of apoptosis regulated by bcl-2.