Figure 3.

Interactions between the microbiome and amongst the host subsystems that may account for variability in response to pathogens. The response of different individuals to pathogens can vary from being resistant, to asymptomatic carriers, to completely sensitive. Host genetics only partially account for this variability. Additional non-heritable influences such as prior exposure to related pathogens and nutritional status of the host could also factor into the response. We argue that the microbiota, because it influences the host health status, also influences the health of the host. Thus, dysbioses is a host risk factor that determines susceptibility to pathogens such as C. difficile infections, and to obesity and autism. The crosstalk between the subsystems provides robustness and maintains health. The crosstalk provides robustness because other subsystems can compensate for the transient loss of one subsystem. The contribution of genetics is shown by blue lines, physiological interactions are shown in green and the influence of microbiota is shown in red.