Comparative transcriptional profiling reveals the striking elevation in the transcriptomic magnitude exclusively of inflammatory mediators and inflammation associated pathways such as cytokine-cytokine receptor interaction, neutrophil extracellular trap formation, natural killer cell mediated cytotoxicity, metabolic pathways, C-type lectin receptor signaling pathway, JAK-STAT signaling pathway, T-cell signaling pathway, phagosome, TNF signaling pathway, PI3K-Akt signaling pathway, Toll-like receptor signaling pathway, chemokine signaling pathway, NOD-like receptor signaling pathway, Th17 cell differentiation, Th1 and Th2 cell differentiation, and B-cell signaling pathway. Several genes associated with these pathways interact, triggering the whole range of inflammatory responses and the genes with the largest discrepancies in the fold-change were the key components of T-cell immune response to
A. flavus. C-type lectin receptors play a major role in regulating antifungal immunity signaling cascades and induce adaptive immunity response to pathogens
49 and C-type lectin receptor signaling pathway associated genes, such as C-type lectin domain family 4, C-type lectin domain family 6, and C-type lectin domain family 7, observed in our study are reported to be involved in antigen uptake at the site of infection either for clearance of the antigen, or for processing and further presentation to T-cells.
50,51 Additionally, they also trigger genes such as caspase recruitment domain family member 9 and spleen tyrosine kinase which in turn triggers NF-κB pathway consequently driving maturation of antigen-presenting cells and shaping antigen-specific priming of T-cells toward effector Th1 and Th17 cell subtypes.
51,52 Interestingly, Dectin-1, which is an important C-type binding receptor, was not identified in our study, although its consecutive signaling genes, such as SYK and CARD9, were upregulated.
36 B-cell lymphoma 3 is also reported to regulate the activation of NF-κB pathway.
53 Previously, in our in vitro studies, we reported the significant upregulation of TLR1, TLR2, and TLR6 upon
A. flavus infection of retinal cells, which corroborated the transcriptomic results.
46 Furthermore, we also observed the upregulation of matrix metalloproteinases, such as MMP3 and MMP9 in our study, which also correlated with the in vitro results.
46 Several studies reported the role of TNF signaling pathway associated genes, such as TNF receptor-associated factor 1 and tumor necrosis factor receptor 2, are linked to the initiation of Th differentiation.
54,55 Genes such as neutrophil cytosolic factor 1 is reported to promote autoreactive CD8+ T-cell activation
55 and tyrosine-protein kinase which are involved in signals mediated by various cytokines or antigen receptors also play a prominent role in T lymphocyte activation and differentiation.
56,57 Interestingly, in addition to the inflammation-associated pathways, genes associated to metabolic pathways were also linked to regulation of immune response and T-cell activation. For instance, diacylglycerol kinase is reported to be the key molecule responsible for immune cell activation and differentiation. They are known to inhibit DAG-mediated signaling in T-cells preventing T-cell hyperactivation. Its downregulation in our study suggests the provision for T-cell activation.
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