Characterization of human pericardial macrophages

Pericardial Immune Cells and Their Evolving Role in Cardiovascular Pathophysiology

The pericardium plays several homeostatic roles to support and maintain everyday cardiac function. Recent advances in techniques and experimental models have allowed for further exploration into the cellular contents of the pericardium itself. Of particular interest are the various immune cell populations present in the space within the pericardial fluid and fat. In contrast to immune cells of the comparable pleura, peritoneum and heart, pericardial immune cells appear to be distinct in their function and phenotype. Specifically, recent work has suggested these cells play critical roles in an array of pathophysiological conditions including myocardial infarction, pericarditis, and post-cardiac surgery complications. In this review, we spotlight the pericardial immune cells currently identified in mice and humans, the pathophysiological role of these cells, and the clinical significance of the immunocardiology axis in cardiovascular health.

Ischemic heart disease: Cellular and molecular immune contributions of the pericardium

Ischemic heart disease promotes complex inflammatory and remodeling pathways which contribute to the development of chronic heart failure. Although blood-derived and local cardiac mediators have traditionally been linked with these processes, the pericardial space has more recently been noted as alternative contributor to the injury response in the heart. The pericardial space contains fluid rich in physiologically active mediators, and immunologically active adipose tissue, which are altered during myocardial infarction. Key immune cells in the pericardial fluid and adipose tissue have been identified which act as mediators for cell recruitment and function after myocardial infarction have been identified in experimental models. Here, we provide an overview of the current understanding of the inflammatory mechanisms of the pericardial space and their role in post-myocardial infarction remodeling and the potential for the use of the pericardial space as a delivery vehicle for treatments to modulate heart healing.

Pericardial fluid and vascular tissue engineering: A preliminary study

BACKGROUND

The heart is surrounded by a membrane called pericardium or pericardial cavity.

OBJECTIVE

In this study, we investigated the pericardial fluid (PF) for coating polycaprolactone (PCL) scaffolds. PFS, which is a PF component, was used for the coating material. In addition to using PFS for surface coating, MED and fetal bovine serum (FBS) were also used for comparison.

METHODS

Pericardial fluid cells (PFSc) isolated from PF were cultured on coated PCL scaffolds for 1, 3, and 5 days. Cell viability was determined using 3-(4, 5-di-methylthiazol- 2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay.

RESULTS

The MTT assay results showed that the viability of cells on PCL scaffold coated with PFS increased over time (P < 0.005), and cell viability was significantly different between PCL scaffolds coated with PFS and non-coated PCL scaffolds. However, cell viability was significantly higher in the PCL scaffolds coated with PFS than non-coated and coated with FBS, MED, and PCL scaffolds. Scanning electron microscopy (SEM) microscopy images and MTT assay indicated that PFSc are attached, proliferated, and spread on PCL scaffolds, especially on PCL scaffolds coated with PFS.

CONCLUSIONS

These results suggest that PFS is a biocompatible material for surface modification of PCL scaffolds, which can be used as a suitable material for tissue engineering applications.

Sterile Injury Repair and Adhesion Formation at Serosal Surfaces

Most multicellular organisms have a major body cavity containing vital organs. This cavity is lined by a mucosa-like serosal surface and filled with serous fluid which suspends many immune cells. Injuries affecting the major body cavity are potentially life-threatening. Here we summarize evidence that unique damage detection and repair mechanisms have evolved to ensure immediate and swift repair of injuries at serosal surfaces. Furthermore, thousands of patients undergo surgery within the abdominal and thoracic cavities each day. While these surgeries are potentially lifesaving, some patients will suffer complications due to inappropriate scar formation when wound healing at serosal surfaces defects. These scars called adhesions cause profound challenges for health care systems and patients. Therefore, reviewing the mechanisms of wound repair at serosal surfaces is of clinical importance. Serosal surfaces will be introduced with a short embryological and microanatomical perspective followed by a discussion of the mechanisms of damage recognition and initiation of sterile inflammation at serosal surfaces. Distinct immune cells populations are free floating within the coelomic (peritoneal) cavity and contribute towards damage recognition and initiation of wound repair. We will highlight the emerging role of resident cavity GATA6+ macrophages in repairing serosal injuries and compare serosal (mesothelial) injuries with injuries to the blood vessel walls. This allows to draw some parallels such as the critical role of the mesothelium in regulating fibrin deposition and how peritoneal macrophages can aggregate in a platelet-like fashion in response to sterile injury. Then, we discuss how serosal wound healing can go wrong, causing adhesions. The current pathogenetic understanding of and potential future therapeutic avenues against adhesions are discussed.

Comparison between optical microscopy and automation for cytometric analysis of pericardial fluids in a cohort of adult subjects undergoing cardiac surgery

Aims

Limited information is available on number and type of cells present in the pericardial fluid (PF). Current evidence and has been garnered with inaccurate application of guidelines for analysis of body fluids. This study was aimed at investigating the performance of automate cytometric analysis of PF in adult subjects.

Methods

Seventy-four consecutive PF samples were analysed with Sysmex XN with a module for body fluid analysis (XN-BF) and optical microscopy (OM). The study also encompassed the assessment of limit of blank, limit of detection and limit of quantitation (LoQ), imprecision, carryover and linearity of XN-BF module.

Results

XN-BF parameters were compared with OM for the following cell classes: total cells (TC), leucocytes (white blood cell [WBC]), polymorphonuclear (PMN) and mononuclear (MN) cells. The relative bias were −4.5%, 71.2%, 108.2% and −47.7%, respectively. Passing and Bablok regression yielded slope comprised between 0.06 for MN and 5.8 for PMN, and intercept between 0.7 for PMN and 220.3 for MN. LoQ was comprised between 3.8×106 and 6.0×106 cells/L for WBC and PMN. Linearity was acceptable and carryover negligible.

Conclusions

PF has a specific cellular composition. Overall, automated cell counting can only be suggested for total number of cells, whereas OM seems still the most reliable option for cell differentiation.

Possible involvement of IL-6-producing tissue-resident macrophages in early-onset pericardial effusion pathogenesis after hematopoietic stem cell transplantation

PURPOSE

Pericardial effusion (PE) is a potentially life-threatening complication following hematopoietic stem cell transplantation (HCT). A higher incidence of early-onset PE, unrelated to graft-versus-host disease, before day 100 after HCT has been reported in pediatric patients, but the pathogenic mechanism is poorly understood. Aiming to determine the pathogenesis of early-onset PE in pediatric patients, we analyzed the cytokine concentration and cell population in the pericardial fluid of four pediatric patients with PE.

METHODS

Between January 2009 and December 2015, four patients requiring pericardiocentesis for clinically significant PE were identified in 60 patients. We evaluated the interleukin-6 (IL-6), interferon-γ, IL-1β, and tumor necrosis factor-α levels in PE. Two patients were available for analysis with intracellular cytokine flow cytometry and a chimerism assay.

RESULTS

All patients showed the accumulation of pericardial macrophages and high concentrations of IL-6 in PE. Notably, the accumulated pericardial macrophages were CD163⁺ CD15⁺ CD14⁺ cells of host origin that produced IL-6.

CONCLUSION

These IL-6-producing tissue-resident macrophages may be key players in the pathogenesis of early-onset PE.

Intravital Imaging of Myeloid Cells: Inflammatory Migration and Resident Patrolling

Myeloid cell recruitment to sites of infection and injury started out as a simple model that has been referred to as the universal concept of leukocyte recruitment. However, as we gain more insight into the different mechanisms, it is becoming clear that each organ and perhaps even each cell has its own unique mechanism of recruitment. Moreover, as the ability to visualize specific cell types in specific organs becomes more accessible, it is also becoming clear that there are resident populations of leukocytes, some within the tissues and others attached to the vasculature of tissues, the latter poised to affect the local environment. In this review, we will first highlight the imaging approaches that have allowed us to gain spectacular insight into locale and function of specific cell types, and then we will discuss what we have learned from this approach as far as myeloid cells are concerned. We will also highlight some of the gaps in our knowledge, which exist almost certainly because of the challenges of being able to visualize certain compartments of the body.

Physiology of pericardial fluid production and drainage

The pericardium is one of the serosal cavities of the mammals. It consists of two anatomical structures closely connected, an external sac of fibrous connective tissue, that is called fibrous pericardium and an internal that is called serous pericardium coating the internal surface of the fibrous pericardium (parietal layer) and the heart (visceral layer) forming the pericardial space. Between these two layers a small amount of fluid exists that is called pericardial fluid. The pericardial fluid is a product of ultrafiltration and is considered to be drained by lymphatic capillary bed mainly. Under normal conditions it provides lubrication during heart beating while the mesothelial cells that line the membrane may also have a role in the absorption of the pericardial fluid along with the pericardial lymphatics. Here, we provide a review of the the current literature regarding the physiology of the pericardial space and the regulation of pericardial fluid turnover and highlight the areas that need to be further investigated.

The composition of normal pericardial fluid and its implications for diagnosing pericardial effusions

BACKGROUND

Pericardial fluid obtained at pericardiocentesis is often subjected to biochemical and hematological analysis, and interpreted using criteria borrowed from pleural effusions. However, the validity and diagnostic yield of this approach is uncertain. Moreover, there is little data regarding the normal composition of the physiological pericardial fluid, which could serve as a reference for pathological effusions.

METHODS

Pericardial fluid from 30 patients undergoing elective open heart surgery was collected. Patients were excluded if they had known pericardial disease, had systemic disorders known to be associated with pericardial disease, or if the fluid samples were hemolytic. The biochemical and hematological parameters of the fluid were determined using standard laboratory techniques, and compared with the results obtained for concurrently drawn venous blood.

RESULTS

The median age of the study population was 64.5 +/- 10.6 years. Chemistry results of soluble molecules were consistent with the plasma ultrafiltrate nature of the fluid. However, fluid lactate dehydrogenase (LDH) level was unexpectedly high, averaging 2.4 times the serum level, and the mean protein level was 0.6 of the serum level. No correlation was found between comorbidities of patients and fluid characteristics. Fluids contained an average of 1430 leukocytes/muL, with a differential count that was predominated by lymphocytes (53.2 +/- 14%) and monocytes (11.6 +/- 6%).

CONCLUSIONS

The composition of the physiologic pericardial fluid is remarkable for high LDH and protein content, and for predominance of lymphocytes. Thus, the biochemical criteria useful for diagnosing pleural effusions are probably not applicable for differentiating transudative from exudative pericardial effusions, and lymphocytosis should be interpreted cautiously.

The biosynthesis of proteoglycans and interstitial collagens by bovine pericardial fibroblasts

The biosynthesis of interstitial collagens (types I and III) and proteoglycans was studied in fibroblasts isolated from the parietal layer of bovine pericardium. Confluent cultures were labeled with Na2 35SO4 for proteoglycans or 14C-proline for collagens. The proteoglycans synthesized by pericardial fibroblasts were purified by DEAE-Sephacel chromatography and further fractionated into three components by gelfilitration. Two minor high molecular weight proteoglycans were shown by SDS-PAGE to be resistant to chondroitinase ABC and AC, and partially degraded by nitrous acid. The major, low molecular weight proteoglycan had a core protein of 45 kDa and is considered to be a dermatan sulfate/chondroitin sulfate proteoglycan since it was resistant to nitrous acid, but digested partially by chondroitinase AC and completely by ABC. The pericardial fibroblasts synthesized predominantly type I collagen and low amounts (about 10%) of type III collagen which was detected by delayed reduction on SDS-PAGE. The data show that pericardial fibroblasts synthesize the same macromolecules that can be extracted from the intact tissue and suggest that the proteoglycan may play a structural as well as physiological role.