Do gliotoxin and mycophenolic acid suppress immune cell function?

Gliotoxin, a metabolite produced by Aspergillus fumigatus, and mycophenolic acid (MPA), a clinical immunosuppressant, profoundly disrupt the immune system's regulatory networks. Together, they impair the cellular machinery required to clear chronic infections and resolve ongoing immune stimulation.

Molecular mechanisms of immune suppression

• Mycophenolic acid (MPA): MPA selectively inhibits inosine-5′-monophosphate dehydrogenase (IMPDH, primarily the type II isoform), trapping the covalent intermediate to halt de novo GMP, GTP, and dGTP synthesis. This severe guanine nucleotide depletion arrests T and B lymphocytes at the G1/S phase of the cell cycle and impairs dendritic cell (DC) maturation by downregulating costimulatory molecules (CD80/CD86) and maturation markers (CD83).
• Gliotoxin: This mycotoxin targets antigen-presenting cells (APCs) by preventing the phosphorylation and degradation of IκB-α, which blocks the nuclear translocation of NF-κB. This blockade prevents the transcription of pro-survival genes, causing ROS-dependent, caspase-mediated apoptosis via Bak in DCs, monocytes, and CD8+ T cells, while drastically reducing the secretion of activating cytokines like IL-12 and TNF-α.

Impact on chronic antigen resolution

• Impaired clonal expansion: Because effective antigen presentation relies on mature, costimulatory-active APCs, the dual suppression of APCs and lymphocytes prevents the activation and expansion of antigen-specific T and B cells.
• Pathogen persistence and cell exhaustion: The host's inability to clear viral, bacterial, or fungal pathogens establishes a self-reinforcing loop. Continuous exposure to unresolved antigen signals under these highly suppressive conditions drives lymphocytes into a state of functional exhaustion, characterized by elevated inhibitory receptors and a total loss of effector capacity.

Bottom line

• Gliotoxin and mycophenolic acid actively prevent the resolution of persistent antigens. By targeting NF-κB signaling and depleting guanosine pools, these compounds halt lymphocyte expansion and paralyze antigen-presenting cells, driving a state of immune exhaustion that allows chronic antigens to persist.