A NON-HUMAN PRIMATE MODEL OF TICK-IMMUNITY

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Ixodes scapularis is an important arthropod vector for pathogens responsible for Lyme disease, rickettsial disease, anaplasmosis, babesiosis, and tick borne encephalitis. There is an unmet need for safe and effective vaccines against these pathogens. Vaccines directed against the tick vector would potentially target multiple pathogens transmitted by the tick. The vertebrate host, upon repeated tick infestation, rejects ticks within 12-24 h and also blocks pathogen transmission. Host immunity directed against crucial tick salivary antigens presumably plays a pivotal role in tick rejection and in the consequent impairment of pathogen transmission. While the phenomenon of acquired tick immunity provides an opportunity to define salivary proteins critical for tick feeding and pathogen transmission, animal models that can demonstrate both tick immunity and viable pathogen transmission are not available. With a focus of Borrelia burgdorferi, the agent of Lyme disease, the current pilot proposal assessed if non-human primates (NHP) might serve such an animal model and enhance efforts to identify vaccines to block tick feeding and pathogen transmission. In Specific Aim 1, two NHPs (Macaca mulatta) were repeatedly infested three times with 10-20 pathogen-free I. scapularis ticks with a three-week resting period between each tick infestation. Optimization of tick placement, and tick infestation studies were conducted over the first 6 months of the funding period at the Tulane National Primate Research Center. The pilot study, albeit limited by the numbers of animals, did not reveal the hallmarks of acquired tick immunity. The ticks successfully engorged as seen by comparable tick attachment and tick weights at all infestations. No significant redness was observed at tick feeding sites upon repeated tick infestations. These observations suggested that NHPs, like mice, might not elicit resistance to ticks. However, histological analysis of the skin biopsies of the tick-feeding sites and reactivity of the sera obtained from these tick-infested animals to tick salivary antigens will be essential. These analyses are pending and are being conducted at the Sections of Comparative Medicine and Infectious Diseases, Yale University. In Specific Aim 2, we challenged the two repeatedly tick-infested NHPs from Aim 1 with 10 Borrelia-infected I.scapularis ticks. Two na¿ve NHPs were similarly challenged with Borrelia-infected ticks. Comparable tick engorgements were observed in both groups. Borrelia burden in the midguts and salivary glands of the fed ticks was also comparable in both groups. However, culture of skin biopsies of the NHPs at 2, 4, 6 and 8 weeks showed no viable spirochetes in the experimental group that was repeatedly infested with ticks. In the control group, one animal demonstrated viable spirochetes. This suggested that upon repeated infestation, NHPs might elicit humoral immunity against tick salivary antigens critical for pathogen transmission. All the animals were sacrificed at the end of 8 weeks and tissues relevant for Lyme disease necropsied for RNA and DNA analysis. These tissues are being processed for quantitative assessment of spirochete burden at the Section of Infectious Diseases, Yale University and studies nearing completion. These results will confirm the NHPs response to tick infestations and reveal the utility of the NHP model to examine tick antigens critical for tick feeding and pathogen transmission.