Immunology Team Contributions to the LSB

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

We previously developed a model system for employing the tools of systems biology to investigate the unexplored roles of many NLRs. In the course of such study, Dr. Subramanian (now leading her own laboratory at the Institute for Systems Biology) observed profound effects of very small changes in intracellular protein concentration on signaling through the NOD1 pathway. Under normal conditions, several miRNAs contribute to maintaining expression of NOD1 below the level leading to ligand-independent gene activation. Alteration in expression of these miRNAs is linked to an increases severity of gastric cancer, which was previously linked to NOD1. These data may be of importance in understanding how small eQTLs linked to inflammatory and autoimmune diseases operate to cause pathology. Based on these findings, we are exploring in various experimental systems whether small (1-2 fold changes in gene expression, as seen with many eQTLs), can lead to disease by imbalancing activation and negative regulatory pathways. We suspect this type of dysregulation might contribute to various autoimmune states. As part of the larger LISB group effort to better understand TLR signaling in macrophages, we have conducted fine grained time and dose studies at the single cell level and on bulk populations looking at a diverse set of downstream signaling events and effector responses. We previously reported quantitative data suggesting that the macrophage response system has evolved to limit potentially damaging inflammation in the face of minor pulses of PAMP or DAMP signals engaging TLR (the steady-state), but to prepare for anti-pathogen responses under such conditions in case these weak signals are not from commensals or normal tissue turnover but from an incipient infection. In a major extension of this macrophage signaling project, we conducted related studies using graded combinations of TLR inputs to develop an understanding of how macrophages decode the multiple PAMP signals of pathogens. The resulting dual dose response matrices showed revealed the more rapid extinction of cytokine production with high single ligand doses than with the lower combined challenges. In particular, high doses of TLR4 ligand caused this early cessation of response. Transcriptional profiling led to identification of a small number of candidate regulators, most described in the literature as having a negative influence on gene expression. Further work showed that the hot spot pattern predicted the capacity of macrophages to discriminate Gram+ from Gram organisms and that again, the Gram-, with their better capacity to trigger TLR4 signaling, showed rapid cytokine shutdown. We then identified a type 1 interferon feedback circuit as responsible for this inhibitory effect, which is independent of the known IL-10 dependent regulatory circuit. These data provide novel insights into the role of type 1 interferon in bacterial infections and also evidence for the crucial role of feedback inhibition in allowing these innate immune cells to discriminate two major classes of pathogens. Based on successful testing of a highly quantitative method for protein quantification by mass spectroscopy, we are engaged with other members of the LISB in developing robust datasets quantifying in a time resolved manner the post-translational modifications of proteins induced upon TLR ligation and building computational models of the TLR signaling process based on these data using the Simmune platform.