Abstract
The immune response towards infection is a dynamic system combating invading pathogens to maintain homeostasis and the integrity of the body. Unbalanced immune response profiles determine many clinical syndromes including sepsis and thus present a major challenge in management of life threatening infections. Consequently, there is a high demand to determine a patient’s immune status and identifying functional parameters for immune dysfunction.
Here, we quantified the global functional status of human innate immune responses by using a human whole-blood model of infection combined with biomathematical modeling. By determining functional parameters of innate immune cell populations after ex vivo whole-blood bacterial (Staphylococcus aureus) and fungal (Candida albicans) infection, we examined cell-specific functional parameters including migration rates or phagocytosis rates in patients that underwent cardiac surgery with extracorporeal circulation. This intervention is known to pose a transient but strong inflammatory stimulus. In addition to a post-operative increase in white blood cell count mainly caused by mobilization of immature neutrophils we find that the surgery induced pro-inflammatory stimulus results in a mitigation of pathogen-specific response patterns that are characteristic for healthy people and baseline results in our patients. Moreover, our model revealed changing rates for pathogen immune evasion, indicating increased inter-pathogenic differences after surgery. This effect was specific for C. albicans and could not be observed for S. aureus. In summary, our model gives insight into immune functionality and might serve as a functional immune assay to record and evaluate innate response patterns towards infection.
Author summary Assessment of a patient’s immune function is critical in many clinical situations. One prominent example is sepsis, which results from a loss of immune homeostasis due to microbial infection. Sepsis is characterized by a plethora of pro- and anti-inflammatory simuli that may occur consecutively or simultaneously and thus any immunomodulatory therapy would require in depth knowledge of an individual patient’s immune status at a given time. Whereas lab-test based immune profiling often relies solely on quantification of cell numbers, we have used an ex vivo whole-blood infection model in combination with biomathematical modeling to quantify functional parameters of innate immune cells in patient blood. A small blood sample of patients undergoing cardiac surgery, which is known to constitute an inflammatory stimulus was infected ex vivo. Functional immune cell parameters were determined using a combination of experimental assays and biomathematical modeling. We show that these parameters change after an inflammatory insult triggered by cardiac surgery and extracorporeal circulation. This does not only interfere with pathogen elimination from blood but also selectively augments the escape of the fungal pathogen Candida albicans from phagocytosis.
