Division of Emerging and Transfusion Transmitted Disease, Center for Biologics Evaluation and Research Food and Drug Administration, Silver Spring, Maryland, United States of America.
Flow Cytometry Core, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
PLoS Negl Trop Dis. 2022 Feb 22;16(2):e0010224. doi: 10.1371/journal.pntd.0010224. eCollection 2022 Feb.
Neutrophils are involved in the initial host responses to pathogens. Neutrophils can activate T cell responses either independently or through indirect involvement of Dendritic cells (DCs). Recently we have demonstrated direct neutrophil-T cell interactions that initiate adaptive immune responses following immunization with live attenuated Leishmania donovani centrin deleted parasite vaccine (LdCen-/-). However, neutrophil-DC interactions in T cell priming in vaccine immunity in general are not known. In this study we evaluated the interaction between neutrophils and DCs during LdCen-/- infection and compared with wild type parasite (LdWT) both in vitro and in vivo.
METHODOLOGY/FINDINGS: LdCen-/- parasite induced increased expression of CCL3 in neutrophils caused higher recruitment of DCs capable of inducing a strong proinflammatory response and elevated co-stimulatory molecule expression compared to LdWT infection. To further illustrate neutrophil-DCs interactions in vivo, we infected LYS-eGFP mice with red fluorescent LdWT/LdCen-/- parasites and sort selected DCs that engulfed the neutrophil containing parasites or DCs that acquired the parasites directly in the ear draining lymph nodes (dLN) 5d post infection. The DCs predominantly acquired the parasites by phagocytosing infected neutrophils. Specifically, DCs containing LdCen-/- parasitized neutrophils exhibited a proinflammatory phenotype, increased expression of costimulatory molecules and initiated higher CD4+T cell priming ex-vivo. Notably, potent DC activation occurred when LdCen-/- parasites were acquired indirectly via engulfment of parasitized neutrophils compared to direct engulfment of LdCen-/- parasites by DCs. Neutrophil depletion in LdCen-/- infected mice significantly abrogated expression of CCL3 resulting in decreased DC recruitment in ear dLN. This event led to poor CD4+Th1 cell priming ex vivo that correlated with attenuated Tbet expression in ear dLN derived CD4+ T cells in vivo.
Collectively, LdCen-/- containing neutrophils phagocytized by DC markedly influence the phenotype and antigen presenting capacity of DCs early on and thus play an immune-regulatory role in shaping vaccine induced host protective response.
中性粒细胞参与宿主对病原体的初始反应。中性粒细胞可以独立激活 T 细胞反应，也可以通过树突状细胞（DC）的间接参与来激活 T 细胞反应。最近，我们已经证明了直接的中性粒细胞-T 细胞相互作用，即在使用活减毒利什曼原虫 centrin 缺失寄生虫疫苗（LdCen-/-）免疫后，可引发适应性免疫反应。然而，一般来说，疫苗免疫中中性粒细胞-DC 相互作用在 T 细胞启动中的作用尚不清楚。在这项研究中，我们评估了 LdCen-/-感染期间中性粒细胞与 DC 之间的相互作用，并与野生型寄生虫（LdWT）进行了比较，包括在体外和体内。
方法/发现：LdCen-/-寄生虫诱导中性粒细胞中 CCL3 的表达增加，导致能够诱导强烈促炎反应和上调共刺激分子表达的 DC 的募集增加，与 LdWT 感染相比。为了进一步说明体内中性粒细胞-DC 相互作用，我们用红色荧光 LdWT/LdCen-/-寄生虫感染 LYS-eGFP 小鼠，并分选在感染后 5 天耳引流淋巴结（dLN）中吞噬含中性粒细胞的寄生虫或直接获得寄生虫的 DC。DC 主要通过吞噬感染的中性粒细胞来获得寄生虫。具体来说，含有 LdCen-/-寄生中性粒细胞的 DC 表现出促炎表型，共刺激分子的表达增加，并在体外启动更高水平的 CD4+T 细胞启动。值得注意的是，与 DC 直接吞噬 LdCen-/-寄生虫相比，当 LdCen-/-寄生虫通过吞噬寄生中性粒细胞间接获得时，会发生有效的 DC 激活。在 LdCen-/-感染的小鼠中耗尽中性粒细胞会显著阻断 CCL3 的表达，导致 ear dLN 中 DC 的募集减少。这一事件导致体外 CD4+Th1 细胞启动减少，与体内 ear dLN 衍生的 CD4+T 细胞中 Tbet 表达减弱相关。
总之，被 DC 吞噬的含 LdCen-/-的中性粒细胞在早期显著影响 DC 的表型和抗原呈递能力，因此在塑造疫苗诱导的宿主保护性反应中发挥免疫调节作用。
