PROJECT SUMMARY The immune response to a peripheral infection is a fundamental feature of the human immune system, providing robust protection from a myriad of infectious agents. The response necessarily invokes the innate immune system, but many features of this orchestrated response are poorly understood, limiting our ability to augment the response to new and ever evolving threats. In particular, the innate response engages the bone marrow to modify the magnitude and dynamics of the response. There are important differences between the mouse (primary model to study the innate immune response) and human innate immune responses, in particular scale and dynamics, and new technologies in 3D cell and tissue culture provide exciting opportunities in the field known as “organ-on-a-chip”. The primary goal of this project is to design, build, and validate an integrated human “ImmuneChip” platform that mimics key dynamic features of the production and trafficking of polymorphonuclear leukocytes (PMN, i.e., neutrophils) between the bone marrow, systemic circulation, and peripheral site of bacterial infection. Developing this technology is important because of the alarming expansion of antibiotic resistance bacteria which will demand creative and alternative approaches to combat. The specific aims are to: 1) design, build, and test a microfluidic ImmuneChip that simulates the homeostatic interaction between bone marrow, systemic circulation, and a sterile skin model; 2) establish a homeostatic circuit in the ImmuneChip in which HSPC expansion, PMN trafficking, and antimicrobial defenses respond to soluble mediators of bacterial infection; and 3) demonstrate an appropriate response to contain a methicillin-resistant (and sensitive) S. aureus peripheral infection within the ImmuneChip, and produce a test- bed for novel biological strategies to combat infection. The in vitro model will be able to uniquely simulate the dynamics of peripheral infection-bone marrow communication including transport barriers, residence time in the circulation, and dilution due to the large difference in the size of the compartments. Accomplishing our primary goal will create a technology that advances a new class of model systems to understand the human response to peripheral infection.