Macrophage Activation Syndrome

Synonymous with secondary hemophagocytic lymphohistiocytosis, macrophage activation syndrome (MAS) is a term used by rheumatologists to describe a potentially life-threatening complication of systemic inflammatory disorders, most commonly systemic juvenile idiopathic arthritis (sJIA) and systemic lupus erythematosus (SLE). Clinical and laboratory features of MAS include sustained fever, hyperferritinemia, pancytopenia, fibrinolytic coagulopathy, and liver dysfunction. Soluble interleukin-2 receptor alpha chain (sCD25) and sCD163 may be elevated, and histopathology often reveals characteristic increased hemophagocytic activity in the bone marrow (and other tissues), with positive CD163 (histiocyte) staining. A common hypothesis as to the pathophysiology of many cases of MAS proposes a defect in lymphocyte cytolytic activity. Specific heterozygous gene mutations in familial HLH-associated cytolytic pathway genes (e.g., PRF1, UNC13D) have been linked to a substantial subset of MAS patients. In addition, the pro-inflammatory cytokine environment, particularly IL-6, has been shown to decrease NK cell cytolytic function. The inability of NK cells and cytolytic CD8 T cells to lyse infected and otherwise activated antigen presenting cells results in prolonged cell-to-cell (innate and adaptive immune cells) interactions and amplification of a pro-inflammatory cytokine cascade. The cytokine storm results in activation of macrophages, causing hemophagocytosis, as well as contributing to multi-organ dysfunction. In addition to macrophages, dendritic cells likely play a critical role in antigen presentation to cytolytic lymphocytes, as well as contributing to cytokine expression. Several cytokines, including tumor necrosis factor, interferon-gamma, and numerous interleukins (i.e., IL-1, IL-6, IL-18, IL-33), have been implicated in the cytokine cascade. In addition to broadly immunosuppressive therapies, novel cytokine targeted treatments are being explored to dampen the overly active immune response that is responsible for much of the pathology seen in MAS.

BackgroundOver the last few years, accumulating data have implicated a role for ferritin as a signaling molecule and direct mediator of the immune system. Hyperferritinemia is associated with a multitude of clinical conditions and with worse prognosis in critically ill patients.DiscussionThere are four uncommon medical conditions characterized by high levels of ferritin, namely the macrophage activation syndrome (MAS), adult onset Still's disease (AOSD), catastrophic antiphospholipid syndrome (cAPS) and septic shock, that share a similar clinical and laboratory features, and also respond to similar treatments, suggesting a common pathogenic mechanism. Ferritin is known to be a pro-inflammatory mediator inducing expression of pro-inflammatory molecules, yet it has opposing actions as a pro-inflammatory and as an immunosuppressant. We propose that the exceptionally high ferritin levels observed in these uncommon clinical conditions are not just the product of the inflammation but rather may contribute to the development of a cytokine storm.SummaryHere we review and compare four clinical conditions and the role of ferritin as an immunomodulator. We would like to propose including these four conditions under a common syndrome entity termed "Hyperferritinemic Syndrome".

Hemophagocytic lymphohistocytosis (HLH) is characterized by fulminant cytokine storm leading to multiple organ dysfunction and high mortality. HLH is classified into familial (fHLH) and into secondary (sHLH). fHLH is rare and it is due to mutations of genes encoding for perforin or excretory granules of natural killer (NK) cells of CD8-lymphocytes. sHLH is also known as macrophage activation syndrome (MAS). Macrophage activation syndrome (MAS) in adults is poorly studied. Main features are fever, hepatosplenomegaly, hepatobiliary dysfunction (HBD), coagulopathy, cytopenia of two to three cell lineages, increased triglycerides and hemophagocytosis in the bone marrow. sHLH/MAS complicates hematologic malignancies, autoimmune disorders and infections mainly of viral origin. Pathogenesis is poorly understood and it is associated with increased activation of macrophages and NK cells. An autocrine loop of interleukin (IL)-1β over-secretion leads to cytokine storm of IL-6, IL-18, ferritin, and interferon-gamma; soluble CD163 is highly increased from macrophages. The true incidence of sHLH/MAS among patients with sepsis has only been studied in the cohort of the Hellenic Sepsis Study Group. Patients meeting the Sepsis-3 criteria and who had positive HSscore or co-presence of HBD and disseminated intravascular coagulation (DIC) were classified as patients with macrophage activation-like syndrome (MALS). The frequency of MALS ranged between 3 and 4% and it was an independent entity associated with early mortality after 10 days. Ferritin was proposed as a diagnostic and surrogate biomarker. Concentrations >4,420 ng/ml were associated with diagnosis of MALS with 97.1% specificity and 98% negative predictive value. Increased ferritin was also associated with increased IL-6, IL-18, IFNγ, and sCD163 and by decreased IL-10/TNFα ratio. A drop of ferritin by 15% the first 48 h was a surrogate finding of favorable outcome. There are 10 on-going trials in adults with sHLH; two for the development of biomarkers and eight for management. Only one of them is focusing in sepsis. The acronym of the trial is PROVIDE (ClinicalTrials.gov NCT03332225) and it is a double-blind randomized clinical trial aiming to deliver to patients with septic shock treatment targeting their precise immune state. Patients diagnosed with MALS are receiving randomized treatment with placebo or the IL-1β blocker anakinra.

ObjectivesMacrophage activation syndrome (MAS) is a severe complication of Still's disease (SD-MAS), but may also, albeit rarely, complicate SLE (SLE-MAS). The clinical profile of SLE-MAS compared with SD-MAS remains unclear, as do the optimal treatment strategies.MethodsA retrospective multicentre cohort of adults with a history of SLE-MAS or SD-MAS was gathered from eight tertiary referral centres. MAS clinical/laboratory features, treatments and outcomes were compared; 'inaugural MAS' was defined if occurring within 6 months from the onset of the underlying disease. Exploratory multivariable profiling assessed for disease-specific features. The SLE-MAS group was also compared with large historical SLE cohorts to identify candidate risk signals.ResultsWhile SD-MAS aligned with the prototypical hyperinflammatory pattern (more marked hyperferritinemia, very high CRP, organomegaly and liver injury; 100% meeting 2016 ACR/EULAR/PRINTO criteria), SLE-MAS (92% meeting criteria) more often featured CNS dysfunction, less liver injury, greater degree of cytopenias including anaemia, with a strong signal of autoimmune haemolysis (73% direct Coombs [DCT] positivity). Therapeutically, IL-1 antagonism was used in seven SLE-MAS with mixed results without any rapid MAS resolution. Mucocutaneous disease, autoimmune haemolysis, CNS involvement, less pronounced female preponderance and much higher DCT positivity dominated the SLE-MAS phenotype compared with historical SLE cohorts comprising 1000, 2228 and 2055 cases each.ConclusionsSLE-MAS diverged from SD-MAS with less organomegaly and liver injury but more pronounced CNS involvement and hematological involvement, the latter strongly linked to red blood cell directed autoantibodies. These findings indicate that SLE-MAS pathogenesis may be divergent and require distinct therapeutic approaches beyond extrapolation from SD-MAS.