Leishmania infantum chagasi induces a dynamic cellular inflammatory response

Leishmania infantum chagasi (Lic) is a pathogenic protozoan parasite and one of the etiological agents of human visceral leishmaniasis (VL). VL is a potentially deadly disease characterized by variable fevers, cachexia, hepatosplenomegaly, and global immune suppression. Many questions regarding the pathogenesis of VL and the mechanisms of host defense during Lic infection remain to be elucidated. The primary focus of this thesis is the relationship between Lic and the mammalian immune system. We studied parasite-host interactions during Lic infection at the molecular, cellular, and organismal level. We generated transgenic parasites that expressed firefly luciferase and/or fluorescent proteins to expand our capacity to detect, observe, and quantify the parasites in a variety of experimental settings with modern analytical methodologies. Using luciferase-expressing Leishmania, we developed an experimental infection model in which parasites were detected and the relative parasite burden in specific anatomical locations could be quantified in a live animal host using bioluminescence imaging. This method allowed the parasite burden to be assessed in the same host throughout the course of infection. Utilizing this model we have made some intriguing observations relating to the kinetics and distribution of the parasite burden over time. The parasite burden was observed primarily in the liver and bone marrow over the first few weeks and then shifts to the spleen and bone marrow. To gain a better understanding of the initial parasite-host immune interactions in vivo, we studied the early inflammatory response after intradermal (i.d.) inoculation. We observed a rapid and abundant influx of neutrophils into the inoculated ears. The neutrophil influx was transient, dose dependent and specific for the local inoculation site. While there was not a significant neutrophil influx into the draining lymph nodes (dLN), there was an increase in the total cellularity and a striking increase in the relative proportion of B cells to T cells over the first week after intradermal parasite challenge. By inoculating transgenic mCherry-Lic we found that neutrophils were the primary parasite-laden host cell in the dermal tissue during the first