Immunogenic Eimeria tenella Glycosylphosphatidylinositol-Anchored Surface Antigens (SAGs) Induce Inflammatory Responses in Avian Macrophages

BackgroundAt least 19 glycosylphosphatidylinositol (GPI)-anchored surface antigens (SAGs) are expressed specifically by second-generation merozoites of Eimeria tenella, but the ability of these proteins to stimulate immune responses in the chicken is unknown. Methodology/Principal FindingsTen SAGs, belonging to two previously defined multigene families (A and B), were expressed as soluble recombinant (r) fusion proteins in E. coli. Chicken macrophages were treated with purified rSAGs and changes in macrophage nitrite production, and in mRNA expression profiles of inducible nitric oxide synthase (iNOS) and of a panel of cytokines were measured. Treatment with rSAGs 4, 5, and 12 induced high levels of macrophage nitric oxide production and IL-1β mRNA transcription that may contribute to the inflammatory response observed during E. tenella infection. Concomitantly, treatment with rSAGs 4, 5 and 12 suppressed the expression of IL-12 and IFN-γ and elevated that of IL-10, suggesting that during infection these molecules may specifically impair the development of cellular mediated immunity. Conclusions/SignificanceIn summary, some E. tenella SAGs appear to differentially modulate chicken innate and humoral immune responses and those derived from multigene family A (especially rSAG 12) may be more strongly linked with E. tenella pathogenicity associated with the endogenous second generation stages.

背景：现有研究表明，柔嫩艾美耳球虫（Eimeria tenella）的第二代裂殖子可特异性表达至少19种糖基磷脂酰肌醇（glycosylphosphatidylinositol, GPI）锚定表面抗原（surface antigens, SAGs），但这类蛋白能否刺激鸡体产生免疫应答仍未明确。方法与主要发现：本研究选取隶属于两个已明确的多基因家族（A与B）的10种SAGs，在大肠杆菌（E. coli）中表达为可溶性重组（r）融合蛋白。将纯化后的重组SAGs（rSAGs）处理鸡巨噬细胞，随后检测巨噬细胞的亚硝酸盐生成水平，以及诱导型一氧化氮合酶（inducible nitric oxide synthase, iNOS）与一组细胞因子的mRNA表达谱变化。实验结果显示，经rSAG 4、5及12处理的巨噬细胞可产生高水平一氧化氮，且IL-1β的mRNA转录水平上调，这一现象可能与柔嫩艾美耳球虫感染过程中观测到的炎症反应相关。与此同时，rSAG 4、5及12处理还可抑制IL-12与干扰素γ（IFN-γ）的表达，并上调IL-10的水平，提示在感染过程中这类分子可能特异性损伤细胞介导免疫的发育。结论与意义：综上，部分柔嫩艾美耳球虫SAGs可差异化调控鸡的固有免疫与体液免疫应答；其中源自多基因家族A的SAGs（尤其是rSAG 12）可能与柔嫩艾美耳球虫内生性第二代虫体阶段相关的致病性存在更强关联。