Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada
J Leukoc Biol. 2015 Aug;98(2):235-48. doi: 10.1189/jlb.2A0215-039RR. Epub 2015 May 14.
Channel catfish (Ictalurus punctatus) IpLITRs belong to the Ig superfamily and regulate innate immune cell effector responses. This study tested the hypothesis that ITAM-dependent and ITAM-independent phagocytic pathways are engaged by different subtypes of the IpLITR family. When stably expressed in RBL-2H3 cells, the ITAM-containing fusion-construct IpLITR 2.6b/IpFcRγ-L stimulated phagocytic responses that were abrogated at suboptimal incubation temperatures and by pharmacological inhibitors of the classic signaling components of the mammalian FcR-dependent phagocytic pathway. Interestingly, the ITIM-containing receptor IpLITR 1.1b also induced phagocytosis through an actin-dependent mechanism, but this process was insensitive to the pharmacological inhibitors tested and remained functional at temperatures as low as 22°C. The IpLITR 1.1b also displayed a unique target-acquisition phenotype that consisted of complex, membranous protrusions, which captured targets in phagocytic cup-like structures but often failed to completely engulf targets. Taken together, these findings suggest that teleost immunoregulatory receptors that associate with ITAM-containing adaptors can engage conserved components of the phagocytic machinery to engulf extracellular targets akin to the classic FcR-mediated response in mammals. Alternatively, IpLITR 1.1b displays a stalled phagocytic phenotype that is likely dependent on the selective recruitment of the minimal molecular machinery required for target capture but results in incomplete target engulfment. Overall, this study demonstrates that IpLITRs can selectively engage distinct components of the phagocytic process and provides important new information regarding the target acquisition as well as internalization mechanisms involved in controlling phagocytic responses across vertebrates.
斑点叉尾鮰（Ictalurus punctatus）IpLITRs 属于 Ig 超家族，调节先天免疫细胞效应反应。本研究检验了以下假说：不同亚型的 IpLITR 家族激活依赖 ITAM 和不依赖 ITAM 的吞噬途径。当在 RBL-2H3 细胞中稳定表达时，含有 ITAM 的融合结构 IpLITR 2.6b/IpFcRγ-L 刺激吞噬反应，该反应在低于最佳孵育温度和经典信号通路的哺乳动物 FcR 依赖的吞噬途径的药理学抑制剂存在时被阻断。有趣的是，含有 ITIM 的受体 IpLITR 1.1b 也通过肌动蛋白依赖性机制诱导吞噬作用，但该过程对所测试的药理学抑制剂不敏感，并且在低至 22°C 的温度下仍保持功能。IpLITR 1.1b 还表现出独特的靶标获取表型，其特征为复杂的、膜状的突起，这些突起捕获吞噬杯中样结构的靶标，但通常不能完全吞噬靶标。总之，这些发现表明，与含有 ITAM 的衔接蛋白相关的硬骨鱼免疫调节受体可以利用吞噬机制的保守成分来吞噬细胞外靶标，类似于哺乳动物中经典的 FcR 介导的反应。或者，IpLITR 1.1b 显示出停滞的吞噬表型，可能依赖于对靶标捕获所需的最小分子机制的选择性募集，但导致不完全的靶标吞噬。总体而言，本研究表明 IpLITRs 可以选择性地参与吞噬过程的不同成分，并提供了有关脊椎动物中控制吞噬反应的靶标获取以及内化机制的重要新信息。
