Mucosal Immunity and the Role of TH1 Cytokines in a Model of Cryptosporidiosis

描述（由申请人提供）： 每年在美国都会报告隐孢子虫病的爆发，主要是由于摄入了被耐氯病原体隐孢子虫污染的水。目前，有限的治疗剂可用于免疫功能低下患者中的隐孢子虫病，这是一个重要的问题，因为免疫功能低下个体中的微小隐孢子虫感染经常发展成慢性、严重的隐孢子虫病，可能危及生命。因此，需要更有效的治疗方法和更好地了解宿主对这种感染的免疫反应。实验隐孢子虫感染小鼠已被用来了解如何细胞介导的免疫发展，并明确定义驱动Th 1或Th 2反应的因素。C.细小病毒感染是IFN-3的产生。几种细胞因子是IFN-3的诱导剂;这些包括IL-12和IL-18。这两种细胞因子在感染中起作用，如IL-12敲除（KO）和IL-18敲除小鼠对C.细小病毒感染关于C中IL-12的信息有限。对于IL-18（一种由上皮细胞和其他免疫细胞产生的细胞因子）的作用，人们了解得更少。我们发现IL-18在C.并且rIL-18是保护性的，即使在不存在IL-12的情况下。推测IL-18在C.通过1）上皮细胞中的先天性应答和2）通过在NK细胞、树突细胞和肠上皮内淋巴细胞（IEL）中诱导IFN-3将应答快速极化到Th 1方向，从而抑制细小病毒感染。具体而言，IL-18增加S7+ IEL的产生，S7 + IEL是一群“高应答”效应细胞，其产生高得多的IFN-3量并且是高度裂解的。IL-18直接作用于IEL或通过激活树突状细胞来激活IEL。此外，树突状细胞可能是肠道中IL-18的关键产生者。我们计划鉴定肠道中表达IL-18的粘膜细胞群并确定其表达水平。我们将使用区分IL-12和IFN-3独立和先天免疫机制的小鼠感染模型来确定IL-18对感染的影响。具体来说，我们将研究其作用（IL-18）在NK，树突状细胞和IEL的激活，并确定这些相同的细胞类型是否可以作为这种细胞因子的反应者和生成者。该建议旨在确定IL-18在抗C.并确定其单独和与其它细胞因子（主要是IL-12，其是IFN-3的关键诱导剂）联合的作用。在免疫功能低下的患者，如HIV感染的个体中，Th 2细胞因子增加，这可能增加患者对需要强Th 1应答的感染的易感性和/或严重性。 公共卫生相关性： 隐孢子虫病是一个重要的原因，是一个重要的疾病，特别是严重的免疫功能低下和老年美国人（一个显着的一部分退伍军人是> 55）。VA是美国最大的HIV护理提供者（每年约有20，000名HIV+患者）。艾滋病是极其重要的退伍军人事务部病人护理使命和一般医学科学。尽管有36-96%的成功率，艾滋病患者的HAART治疗可能会因耐药性或吸收不良而失败。尽管CD 4水平升高，但由于细胞因子或效应CD 4功能失调，对机会性感染的易感性可能持续存在。抗逆转录病毒治疗失败率在某些群体中较高，如非洲裔美国人，即使在提供平等的护理机会时也是如此（Hartzell等人，2006年）。由于抗隐孢子虫治疗免疫功能低下的人是有限的，往往是无效的，了解隐孢子虫病的免疫反应，应促进免疫调节治疗，以预防和控制C的发展。以及其他机会性感染。

DESCRIPTION (provided by applicant): Every year outbreaks of cryptosporidiosis are reported in the US, mainly due to ingestion of water that has been contaminated by the chlorine-resistant pathogen Cryptosporidium. Currently, limited therapeutic agents are available for cryptosporidiosis among immunocompromised patients, which is an important concern since Cryptosporidium parvum infections in immunocompromised individuals often develop into chronic, severe cryptosporidiosis that can become life threatening. Thus there is a need for a more effective therapy and a better understanding of host immune responses to this infection. Experimental Cryptosporidium infections in mice have been used to understand how cell-mediated immunity develops and to specifically define the factors driving Th1 or Th2 responses. A major factor in resistance to C. parvum infection is the production of IFN-3. Several cytokines are inducers of IFN-3; these include IL-12, and IL-18. Both of these cytokines play a role in infection as evidenced by the fact that IL-12 knockout (KO) and IL-18 KO mice are highly susceptible to C. parvum infection. Limited information exists about IL-12 in C. parvum infections; even less is known about the role of IL-18, a cytokine produced by epithelial cells and other immune cells. We have found that IL-18 is up- regulated in response to C. parvum infection and that rIL-18 is protective, even in the absence of IL-12. It is hypothesized that IL-18 has a significant role in C. parvum infection through 1) innate responses in the epithelial cells and 2) rapidly polarizing the response to a Th1 direction by inducing IFN-3 in NK cells, dendritic cells, and intestinal intraepithelial lymphocytes (IELs). Specifically, IL-18 augments the production of S7+ IELs, a population of 'high-responder' effector cells that produce much higher amounts of IFN-3 and are highly lytic. IL-18 acts either directly on IELs or by activating dendritic cells that activate IELs. In addition, dendritic cells may be a key generator of IL-18 in the intestinal tract. We plan to identify the IL-18 expressing mucosal cell populations in the intestinal tract and determine their expression levels. We will determine the impact of IL-18 on infection using murine models of infection that discern IL-12 and IFN-3 independent and innate immune mechanisms. Specifically, we will investigate its role (IL-18) in the activation of NK, dendritic cells, and IELs and determine if these same cell types may act as both responders and generators of this cytokine. This proposal aims to define the role IL-18 plays in resistance to C. parvum and to determine its effect alone and in conjunction with other cytokines, primarily IL-12, that are key inducers of IFN-3. In immunocompromised patients, such as HIV-infected individuals, there is an increase in Th2 cytokines, which may increase patient susceptibility and/or severity of infections that require strong Th1 responses. PUBLIC HEALTH RELEVANCE: Cryptosporidium is a significant cause of diarrheal illness and is particularly severe in immunocompromised and older Americans (a significant portion of Veterans are > 55). The VA is the single largest provider of HIV care in the US (~20,000 HIV+ patients seen annually). AIDS is of extreme importance to the VA patient care mission and to general medical science. Despite a 36-96% success rate, HAART treatment for AIDS patients can fail due to drug resistance or malabsorption. Susceptibility to opportunistic infections may persist despite increased CD4 levels, due to dysregulated cytokines or effector CD4 functions. Antiretroviral failure is higher in certain groups, such as African-Americans, even when equal access to care is provided (Hartzell et al., 2006). Since anticryptosporidial therapy in immunocompromised individuals is limited and often ineffective, understanding the immune response to cryptosporidiosis should facilitate the development of immunomodulating therapies that augment immune responses in order to prevent and control C. parvum and other opportunistic infections.