Quantifying innate immune response of an insect host challenged by non-replicative immune inducers

Non-linear immune response is one of the causes of multi-stability of infection outcomes. In order to avoid the uncertainty caused by multi-stability in experiments, one needs to quantitatively measure immune response and other traits as well. Here, we took a quantitative approach, which combines mathematical model and time-series data, to measure the immune response of the Tenebrio moliter challenged by non-replicative immune inducers. The results showed that the host immunity that characterized by in-vitro bacterial killing rapidly mounted after immune challenging, then slowly declined to an undetectable level within 100 h. We then quantified the immunity at 15 h after challenging. The results showed that immune response was non-linearly correlated with the titter of inducer, which fits well to a Hill-like function. Our results have verified the non-linear immune response with respect to amount of invading pathogens and may also help to rigorously test the concepts and theories in host–pathogen interaction, such as resistance and tolerance.