Can gliotoxin suppress immune cell activity and weaken microbial clearance?

Gliotoxin, a secondary metabolite of Aspergillus fumigatus, has moderate-strength experimental support as a suppressor of selected host immune functions. The most coherent implication is impaired antifungal defense, particularly when innate phagocyte function is important.

Clinical and experimental immune effects

• In human neutrophils, gliotoxin inhibited zymosan phagocytosis at 30–100 ng/mL (92–306 nM) and reduced reactive-oxygen-species production at 107 nM within 30 minutes, consistent with reduced oxidative killing capacity.
• In primary human macrophages, 1.53 μM gliotoxin disrupted PtdIns(3,4,5)P3 signaling and reduced phagocytosis. Reported macrophage apoptosis over roughly 0.3–3 μM means part of the apparent suppression may arise from cellular injury.
• In CMV- or SEB-stimulated human cultures, 50 ng/mL reduced cytokine-producing CD4+ and CD8+ T-cell responses by about half; some responses were nearly abolished at 300–400 ng/mL. This appears driven chiefly by monocyte/dendritic-cell damage and impaired antigen presentation, rather than definitively direct T-cell inhibition.

Mechanistic basis for weakened clearance

• Gliotoxin can disrupt macrophage conidial uptake through altered integrin/actin-related signaling, inhibit LC3-associated phagocytosis, and reduce leukotriene B4 production.
• It inhibits NF-κB activation, including prevention of IκBα degradation, and impairs neutrophil NADPH-oxidase activation and superoxide generation.
• In hydrocortisone-immunosuppressed non-neutropenic mice, a gliotoxin-deficient gliP mutant was less virulent and did not suppress neutrophil oxidative burst; this phenotype was not seen in neutropenic models, underscoring neutrophil-dependent host context.

Bottom line

• Gliotoxin plausibly weakens microbial—especially A. fumigatus—clearance by compromising macrophage uptake/processing, neutrophil oxidative responses, and antigen-presenting-cell-supported T-cell responses. The conclusion is supported primarily by coherent in-vitro and mechanistic animal evidence, with uncertain clinical relevance at human exposure levels.