Role of IL-7 and Integrin alpha4beta7 in Human Immunodeficiency Virus Infection

白细胞介素7(IL-7)是体内主要的T细胞稳态因子，在发生淋巴细胞减少(淋巴细胞丧失)时，对重建正常的T淋巴细胞库至关重要。我们以前的工作表明，IL-7是主要的肠道归巢整合素α4beta7(A4b7)的有效诱导剂，从而将NAVE T细胞重定向到肠道，肠道是HIV-1复制的主要解剖部位。此外，我们还发现，在HIV-1病毒粒子从感染细胞中排出的过程中，A4b7被整合到病毒粒子中。病毒粒子掺入的a4b7具有功能活性，因为它能够与其天然配体MAdCAM-1结合，并在小鼠模型中促进HIV-1病毒颗粒的肠道归巢。重要的是，在HIV感染患者和SIV感染的猕猴体内也存在a4b7掺入，这表明它可能是促进和维持肠道内HIV-1感染的一个关键毒力因子，特别是在HIV-1感染的早期阶段。我们还证明了另一个宿主受体，P-选择素糖蛋白配体-1(PSGL-1/CD162)，在体外和体内都被整合到HIV-1病毒粒子中。我们已经开始研究包含A4b7的SIV病毒粒子在猕猴模型中是否具有更强的介导病毒传播的能力。因此，无论是否掺入A4b7，均一的SIVmac239分子克隆被用于雌性猕猴的阴道传播研究。初步结果表明，结合了a4b7的存在可能会促进感染，尽管在不同的猕猴中传播是高度不同的，正如在对近交系动物的研究中所预期的那样。进一步的研究正在进行中，以评估通过直肠途径传播SIV时，掺入4b7基因所带来的优势是否更显著。 关于IL-7，我们发现了这种细胞因子的新功能，在超稳态浓度下，IL-7是一种有效的抗HIV趋化因子(即RANTES/CCL5、MIP-1a/CCL3和MIP-1b/CCL4)和其他参与抗微生物免疫反应的细胞因子的诱导剂。这种效应在没有任何其他伴随刺激的情况下发生，但需要T细胞和单核细胞之间活跃的和接触相关的串扰。对介导这种IL-7效应的机制的深入描述表明了肿瘤坏死因子-α的关键作用。我们还鉴定了介导IL-7效应的信号转导，并进行了RNAseq分析，揭示了针对抗微生物防御准备的复杂基因表达程序。我们重新评估了10年前我们在猕猴体内进行的IL-7体内治疗研究的微阵列结果(Vassena等人，PLoS Path 2012)，并发现许多由IL-7体外激活的基因在猕猴模型中也是在体内诱导的。最后，我们已经开始研究干扰素-α作为IL-7效应的潜在拮抗剂的作用。总体而言，我们的结果表明，IL-7通过协调招募多种细胞因子和趋化因子，启动了一项针对入侵微生物的免疫防御计划。这些结果说明了一种新的潜在的抗微生物控制机制，该机制不需要触发完整的T细胞激活程序，并且身体可以在淋巴细胞减少的情况下实施，试图重建失去的免疫功能，以及促进非溶细胞性免疫介导的抑制HIV-1。

Interleukin-7 (IL-7) is the principal T-cell homeostatic factor in the body and is critical to reconstitute the normal T-lymphocyte pool when lymphopenia (loss of lymphocytes) occurs. Our previous work demonstrated that IL-7 is a potent inducer of the main gut-homing integrin, alpha4beta7 (a4b7), and thereby redirects nave T cells to the intestine, which is a primary anatomical site for HIV-1 replication. Furthermore, we found that a4b7 is incorporated into the HIV-1 virion during its egress from infected cells. Virion-incorporated a4b7 is functionally active as it is able to bind to its natural ligand, MAdCAM-1, and promote gut homing of HIV-1 viral particles in a mouse model. Importantly, a4b7 incorporation also occurs in vivo in HIV-infected patients and SIV-infected macaques, suggesting that it may be a critical virulence factor that promotes and sustains HIV-1 infection of the gut compartment, particularly during the early phases of HIV-1 infection. We have also demonstrated that another host receptor, P-selectin glycoprotein ligand-1 (PSGL-1/CD162), is incorporated into HIV-1 virions both in vitro and in vivo. We have started to investigate whether SIV virions containing incorporated a4b7 have an increased capacity to mediate viral transmission in a macaque model. Thus, a homogeneous molecular clone of SIVmac239 was produced either with or without incorporated a4b7 and used for transmission studies by the vaginal route in female macaques. Preliminary results suggest that the presence of incorporated a4b7 may facilitate infection, even though transmission was highly variable in different macaques, as expected in studies with outbred animals. Further studies are ongoing to evaluate if the advantage conferred by a4b7 incorporation may be more significant upon SIV transmission by the intrarectal route. With regard to IL-7, we have discovered a new function of this cytokine, by showing that, at suprahomeostatic concentrations, IL-7 is a potent inducer of anti-HIV chemokines (i.e., RANTES/CCL5, MIP-1a/CCL3 and MIP-1b/CCL4) and other cytokines involved in antimicrobial immune responses. This effect occurs in the absence of any other concomitant stimulation but requires an active and contact-dependent cross-talk between T cells and monocytes. An in-depth characterization of the mechanisms that mediate this IL-7 effect has demonstrated a key role of TNF-alpha. We have also characterized the signal transduction that mediates the IL-7 effects and performed RNAseq analysis, which has unraveled a complex program of gene expression aimed at antimicrobial defense readiness. We have re-evaluated the microarray results from a study of in vivo IL-7 treatment that we had performed in macaques 10 years ago (Vassena et al., PLoS Path 2012) and found that many of the genes activated in vitro by IL-7 are also induced in vivo in the macaque model. Finally, we have started to study the effect of interferon-alpha as a potential antagonist of the IL-7 effects. Overall, our results demonstrate that IL-7 initiates a program of immunologic defense against invading microbes through the concerted recruitment of multiple cytokines and chemokines. These results illustrate a novel potential mechanism of antimicrobial control that does not require the triggering of a full T-cell activation program and that the body may implement under conditions of lymphopenia in an attempt to reconstitute the lost immune function as well as to facilitate non-cytolytic immune-mediated suppression of HIV-1.