Recent research into the predictability of infection outcomes within isogenic populations of Caenorhabditis elegans has revealed that susceptibility to pathogens is shaped by maternal circadian timing. It was discovered that individual-level immune differences can be resolved under standardized conditions by identifying the basal expression of the infection response gene irg-5 as a predictive pre-infection biomarker.
Individuals exhibiting high-basal expression of this gene, categorized as Hi-GFP animals, were found to be significantly more susceptible to Pseudomonas aeruginosa infection than their Lo-GFP counterparts. Other physiological traits, including pharyngeal pumping, locomotion, and body size, were determined not to be predictive of survival.
Genetic Regulation of Immune Variability
The genetic regulation of this variability was explored through a high-throughput genome-wide RNAi screen of 16,749 genes, which identified the MEIS homeobox protein UNC-62 as a critical regulator. UNC-62 was established to act as a transcriptional suppressor that physically binds to the irg-5 promoter to prevent its expression under basal conditions.
It was further demonstrated that the activation of irg-5 following the inhibition of UNC-62 requires the p38 mitogen-activated protein kinase (PMK-1) pathway and the GATA binding erythroid-like transcription factor (ELT-2). Genetic mimicry of the high-basal activity found in pre-activated individuals was achieved through the inhibition of UNC-62, which resulted in an enhanced susceptibility phenotype.
Maternal and Circadian Influences
The distribution of immune states within the population was found to be modulated by maternal circadian entrainment. Maternal hermaphrodites were subjected to 12-hour alternating cycles of light/dark and fluctuating temperatures to mimic natural environmental conditions. An oscillatory pattern was detected in the frequency of pre-activated progeny produced by these entrained mothers, a rhythm that was absent in those kept under constant conditions. Furthermore, an intergenerational transfer of immune status was noted, as Hi-GFP mothers were observed to produce a significantly higher percentage of Hi-GFP offspring than Lo-GFP mothers.
Specific clock genes were identified as regulators of this phenotypic distribution:
1] nhr-23: The knockdown of this gene eliminates the rhythmic oscillation of the frequency of pre-activated individuals in the progeny.
2] kin-20 and lin-42: While these clock-associated genes were tested, nhr-23 was pinpointed as the primary controller of this rhythmic immune variability.
Implications for Evolutionary Biology
This study provides evidence of phenotypic heterogeneity in a multicellular isogenic organism, suggesting that such variability serves as an adaptive strategy for population-level resilience. By ensuring that a subpopulation is “primed” or regulated differently, the fitness of the clonal population is potentially increased against unpredictable pathogen pressures. These findings highlight the role of nongenetic and circadian factors in shaping immunity, offering potential implications for the study of human immune variation and personalized medicine.
Source:
Science Advances
Jonathan Lalsiamthara et al, Circadian-shaped immune variability predicts infection outcome, Science Advances (2026). DOI: 10.1126/sciadv.adx8112
