Dengue Literature Review

Macrophage Activation Syndrome in Dengue

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Macrophage Activation Syndrome in Dengue

Overview

Macrophage Activation Syndrome (MAS) — also called secondary hemophagocytic lymphohistiocytosis (HLH) or virus-associated hemophagocytic syndrome — is a life-threatening hyperinflammatory syndrome characterised by excessive and dysregulated activation of macrophages and CD8+ T cells. It presents clinically with persistent fever, cytopenias (affecting at least 2 of 3 blood lineages), hepatosplenomegaly, and markedly elevated serum ferritin and triglycerides. When triggered by infection rather than by a primary genetic defect or autoimmune disease, it is classified as secondary MAS.

Dengue virus is an established trigger of secondary MAS, with case reports from multiple endemic countries. MAS in the context of dengue is a distinct immunopathological syndrome that differs mechanistically from the classical dengue autoimmune pathway (NS1 molecular mimicry → anti-platelet/anti-endothelial antibodies). Its pathogenesis is macrophage- and T cell-driven, and conventional antinuclear autoantibodies (ANA, anti-dsDNA) are typically absent in documented cases — a critical distinction from other dengue autoimmune manifestations.

Key Points from Literature

Clinical Spectrum in Dengue (Morel2014)

Morel2014 - Autoimmune Response in Children With Dengue provides the most detailed dengue-MAS case series in this wiki (3 cases from Paraguay):

Case 2 (3-year-old) — met HLH-2004 criteria (without bone marrow hemophagocytosis):

  • Fever (persistent 3 weeks), hepatosplenomegaly (liver 9 cm, spleen 3 cm below costal margins), petechiae
  • Leucopenia with neutropenia (leukocytes 3000/ml, neutrophils 900/ml)
  • Anemia (Hgb 8.2 g/dl)
  • Hypertriglyceridemia (470 mg/dl)
  • Hyperferritinemia (1150 mg/dl)
  • Dengue confirmed: NS1 antigen positive
  • ANA, anti-dsDNA, and RF all negative
  • Responded well to methylprednisolone boluses

Case 3 (3-month-old infant) — met HLH-2004 criteria (without bone marrow hemophagocytosis):

  • Fever, hepatosplenomegaly (liver 6 cm below costal margin), vomiting, diarrhea
  • Leucopenia with neutropenia (leukocytes 3500/ml, neutrophils 1100/ml)
  • Anemia (Hgb 8.0 g/dl, progressive)
  • Hypertriglyceridemia (383 mg/dl)
  • Hyperferritinemia (3828 mg/dl — the most severely elevated in the series)
  • Dengue confirmed: NS1 antigen positive
  • ANA, anti-dsDNA, and RF all negative
  • Responded well to methylprednisolone boluses

Both MAS cases met 5 of 8 HLH-2004 criteria. Notably, neither demonstrated bone marrow hemophagocytosis on aspirate — the most classic HLH finding — yet both met the threshold for clinical diagnosis by other criteria.

HLH-2004 Diagnostic Criteria

Per the HLH-2004 protocol (cited in Morel2014), diagnosis requires either a molecular HLH diagnosis or fulfillment of ≥5 of 8 criteria:

  1. Fever
  2. Splenomegaly
  3. Cytopenias (≥2 lineages): Hgb <9.0 g/L, platelets <100,000/mm³, neutrophils <1000/mm³
  4. Hypertriglyceridemia (≥265 mg/dl) and/or hypofibrinogenemia (≤1.5 g/L)
  5. Hemophagocytosis in bone marrow, spleen, lymph nodes, or CSF
  6. Low or absent NK cell activity
  7. Elevated serum ferritin (≥500 mg/L)
  8. Soluble CD25 elevated above age-normal range

Both Morel2014 cases lacked criterion 5 (hemophagocytosis on biopsy) but met criteria 1, 2, 3, 4, and 7 — fulfilling the 5-of-8 threshold.

Additional MAS + Nephrotic Syndrome Case (Palacios2016, via Lai et al.)

Palacios2016 - Autoimmunity in Dengue Literature Review cites a MAS case complicated by nephrotic syndrome (Lai et al. 2012, France): a 55-year-old woman with neutropenia, lymphopenia, and hemophagocytosis on myelogram, who developed nephrotic syndrome during hospitalisation. Dengue reinfection was confirmed by NS1 antigen positive plus positive IgG and IgM serology. This extends dengue-associated MAS beyond the paediatric population and documents renal involvement (nephrotic syndrome) as an additional MAS-dengue complication.

Macrophage Activation: Mechanism

Secondary MAS is mediated by prolonged and excessive activation of antigen-presenting cells (macrophages, histiocytes) and CD8+ T lymphocytes. Hemophagocytosis, when present, is mediated through CD163 (scavenger receptor B1) on activated macrophages and histiocytes. The resulting cytokine hypersecretion (particularly IL-18, IFN-gamma, TNF-alpha, IL-6, and IL-1) drives the multisystem inflammation.

In the dengue context, proposed triggers include:

  • NS1-TLR4 activation of macrophages (see NS1 Protein) — sNS1 acting as an endotoxin analogue, triggering pro-inflammatory cytokine cascades
  • Viral load–driven macrophage overactivation in heavily infected monocyte-macrophages (which are permissive DV target cells)
  • ADE-mediated FcγR entry into macrophages, amplifying macrophage infection and activation (see Antibody-Dependent Enhancement)

The absence of ANA/anti-dsDNA in Morel2014’s MAS cases is consistent with this mechanism: MAS is driven by innate/cellular immune hyperactivation, not by autoantibody-mediated B cell pathology. This distinguishes dengue-MAS from dengue autoimmunity of the NS1 molecular mimicry type.

Relationship to Other Dengue Autoimmune Mechanisms

The dengue-autoimmune literature (Lin2006, Lin2011, Wan2012) documents a different pathway: NS1 molecular mimicry → anti-platelet/anti-endothelial autoantibodies → thrombocytopenia and vascular leakage. That pathway:

  • Produces elevated autoantibodies detectable by serology
  • Is severity-correlated (higher in DHF/DSS than DF, per Wan2012)
  • Is NS1-dependent (absorption with NS1 removes cross-reactivity)

Dengue-triggered MAS, by contrast:

  • Is associated with negative conventional ANA/anti-dsDNA
  • Operates through macrophage hyperactivation and hypercytokinemia
  • Is classified with secondary HLH, a syndrome caused by many pathogens (EBV, VZV, parvovirus B19, hepatitis A, CMV, leishmaniasis, etc.) in addition to dengue

These two pathways are not mutually exclusive — both can occur in the same patient — but they likely reflect different host immune configurations. Whether dengue patients who develop MAS have distinct host genetic factors (e.g., HLH predisposition variants in PRF1, UNC13D, STX11) is unknown but biologically plausible.

Treatment

Both MAS cases in Morel2014 responded well to methylprednisolone boluses. The Morel authors note that secondary MAS associated with autoimmune diseases or viral infections carries a significant mortality rate if untreated. The HLH treatment protocol (glucocorticoids, cyclosporine, etoposide, or anti-thymocyte globulin) was referenced for more refractory cases.

The key practical implication: dengue-triggered MAS may be clinically confused with primary autoimmune disease (SLE, juvenile idiopathic arthritis) in endemic settings. The ANA-negative pattern in the most severe MAS cases means that a negative ANA result does NOT rule out severe immune-mediated dengue complication.

Contradictions & Debates

  • ANA-negative MAS vs. autoantibody-severity correlation: Wan2012 (cited in Palacios2016 - Autoimmunity in Dengue Literature Review) reports that anti-endothelial cell autoantibody levels are higher in DHF/DSS than in DF. Morel2014’s MAS cases are the most severe in that series yet have NO conventional autoantibodies. Resolution: Wan2012 measured flow cytometric anti-endothelial cell antibodies (not standard ANA/anti-dsDNA), and MAS is not an autoantibody-mediated syndrome. The two observations target different biological phenomena.

  • Absence of hemophagocytosis: Both Morel2014 MAS cases lacked bone marrow hemophagocytosis on aspirate, which is the defining histological finding in HLH. The authors justify the MAS/HLH diagnosis on the other criteria. Whether dengue-triggered MAS reliably produces hemophagocytosis or whether it represents a related but distinct macrophage-hyperactivation phenotype is uncertain.

  • Age and MAS susceptibility: Cases 2 and 3 were very young (3 years, 3 months). Young children may be more susceptible to dengue-triggered MAS because their HLH predisposition loci are more likely to carry heterozygous variants that lower the macrophage activation threshold below what is clinically symptomatic in healthy adults with full functional reserves.

Sources

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