Characterization and function of the inflammatory response to infection by a gastrointestinal nematode parasite : new insights into protective Th2 responses /

by Anthony, Robert McCullough

Title of Dissertation: Characterization and Function of the Inflammatory Response to Infection by a Gastrointestinal Nematode Parasite: New Insights into Protective Th2 Responses. Name: Robert McCullough Anthony, Molecular and Cell Biology Graduate Program, USUHS, Bethesda, MD 20814 Dissertation Directed by: William C. Gause, Ph.D., Senior Associate Dean of Research, Professor of Medicine, Director of Center for Host Defense and Inflammation, UMDNJ, Newark, NJ 07101 (current address). Professor, Department of Microbiology and Immunology, USUHS, Bethesda, MD 20814 Effective immune responses to infectious diseases involve recognition of invading pathogens and result in appropriate primary and secondary reactions mediating host protection. Although these responses against many bacteria and viruses have been characterized extensively, Th2 effector mechanisms leading to host-protection remain elusive. Using an infectious model employing a natural murine gastrointestinal nematode parasite, Heligmosomoides polygyrus, we characterized the immune cell infiltrate surrounding invasive larval parasites in the small intestinal muscosa and submucosa (host:parasite interface) during early stages of a secondary infection. A primary is chronic, with established adult parasites detectable up to four months post infection, where as the parasites are naturally cleared from the intestinal lumen by 14 days follow challenge. This distinction between primary and secondary H. polygyrus infections allows a clear iii readout of protective immunity, making this infectious model useful for examining protective secondary Th2 responses. A distinct and highly reproducible leukocyte architecture developed by the fourth day post challenge, which included Gr1+ neutrophils amassing adjacent to the parasite, and CD4+ T cells, CD11c+ dendritic cells, and MBP-1+ eosinophils surrounding the parasite in the lamina propria. Additionally, laser capture microdissected (LCM) samples from the host:parasite interface featured upregulated Th2 cytokine mRNAs relative to untreated intestinal tissue. This localized inflammatory response differed during primary infection, as CD4+ T cells did not infiltrate the host:parasite interface, and there were no increases in cytokine expression. These findings were extended to show that the peripheral inflammation during the memory Th2 response at the host:parasite interface is essential for host-protection leading to worm expulsion. Memory CD4+ T cells that express Th2 cytokines rapidly accumulate around the invading parasite in the intestinal submucosa, and induce the alternative activation of macrophages (IL-4Rhi, CD206+, arginase-1+, Fizz1+, Ym1+, iNOS-). Alternatively activated macrophages metabolize the amino acid, arginine, by the enzyme arginase-1, which is essential for their differentiation and effector functions. Through intervention experiments, our findings demonstrate that macrophages and arginase contribute to the natural clearance of a secondary H. polygyrus infection. These observations provide new insights into mechanisms of host-protection mediated by Th2 responses, and establish a novel, protective role for alternatively activated macrophages. iv Characterization and Function of the Inflammatory Response to Infection by a Gastrointestinal Nematode Parasite: New Insights into Protective Th2 Responses. by Robert McCullough Anthony Dissertation submitted to the faculty of the Molecular and Cell Biology Graduate Program of the Uniformed Services University of the Health Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy, May 2006. v