D2.169 - TLR8-dependent differential signal transduction induced by methanogenic archaea is controlled by NF-κB p65- and STAT1/2-regulated gene classes

Methanobrevibacter smithii (Msm) and Methanosphaera stadtmanae (Mst) are the most abundant archaeal species in the human gut. In children, the presence of Mst, but not Msm, has been linked to a lower risk for asthma. Archaea lack canonical bacterial cell wall motifs yet show immune activity through activation of endosomal TLR8 by its RNA.

To dissect the molecular mechanism of differential activation by these two archaeal species, we used time-resolved RNA-seq in human PBMCs and revealed a conserved innate program shared with bacterial or viral stimuli, but with distinct kinetics.

M. stadtmanae triggers earlier, stronger activation, whereas M. smithii responds more gradually. Shared early-upregulated genes segregated into two classes. Class I genes are preferentially induced by M. stadtmanae, while Class II genes are similarly induced by both. Mechanistically, higher early uptake of M. stadtmanae delivers stronger endosomal input to TLR8, which enables NF-κB p65 recruitment at Class I promoters, whereas Class II genes are driven by STAT1/2 and require only minimal uptake. Consistently, archaeal RNA dose-response experiments showed low-dose activation of Class II but a higher threshold for Class I.

These results define an input-tuned, TLR8-governed logic by which archaeal inputs gate immune programs and may help explain divergent archaeal disease associations.