FOOD ALLERGEN TRANSPORT BY HUMAN INTESTINAL CELLS : A STUDY USING CULTURED CACO-2 CELLS

肠上皮细胞(IECS)除了作为粘膜屏障和运输营养物质外，还具有抗原提呈细胞(APC)的功能。蛋白水解法修饰蛋白质抗原是Th细胞抗原呈递的主要步骤之一。我们使用Caco-2肠上皮细胞系来研究食物抗原卵清蛋白(OVA)的跨上皮转运。我们还在Caco-2细胞层中检测了促炎细胞因子干扰素-γ(干扰素-γ)对抗原运输过程的影响。Caco-2细胞层将完整的和降解的OVA从粘膜转移到浆膜侧。干扰素-γ促进卵清蛋白的转运，大部分卵清蛋白在细胞内的转运被降解。我们还用免疫组织化学方法检测了Caco-2细胞对OVA的摄取。Caco-2细胞以时间依赖的方式掺入卵清蛋白，干扰素-γ显著促进抗原内化。流式细胞仪检测还显示，干扰素-γ可促进卵清蛋白内化。我们还测定了低浓度和高浓度干扰素-γ对粘膜通透性和荧光素卵清蛋白内化的影响。尽管10和50 ng/mL干扰素-γ对粘膜通透性的刺激程度相同，但50和10 ng/mL干扰素-γ孵育的Caco-2细胞对FITC-OVA的内在化程度高于10 ng/mL干扰素-OVA。这些结果提示，干扰素-γ对肠粘膜通透性和肠上皮细胞抗原内化的影响可能是通过不同的机制实现的。因此，较高浓度的干扰素-γ可刺激IECs摄取、加工和转运食物抗原。

Besides functioning as a mucosal barrier and transporting nutrients, intestinal epithelial cells (IECs) also serve as antigen presenting cells (APCs). Modification of protein antigens by proteolysis is one of the principal steps in antigen presentation to Th cells. We used a Caco-2 intestinal epithelial cell line to investigate the transepithelial transport of the dietary antigen, ovalbumin (OVA). We also examined in Caco-2 cell layers, the effects of the proinflammatory cytokine interferon-γ (IFN-γ) on the antigen transport process. Caco-2 cell layers transferred both intact and degraded OVA from the mucosal to the serosal side. IFN-γ stimulated OVA transport and most of the transported OVA in such cells was degraded. We also examined OVA uptake by Caco-2 cells using immunohistochemical means. Caco-2 cells incorporated OVA in a time-dependent manner and IFN-γ significantly enhanced antigen internalization. Flow cytometry also demonstrated that IFN-γ elevated the internalization of FITC-OVA. We also determined the effect of low and high concentrations of IFN-γ on mucosal permeability and internalization of FITC-OVA. Although both 10 and 50 ng/mL IFN-γ stimulated mucosal permeability to same extent, more FITC-OVA was internalized by Caco-2 cells incubated with 50, than with 10 ng/mL IFN-γ. These results suggest that the effects of IFN-γ on mucosal permeability and on the internalization of antigens by intestinal epithelial cells are brought about by different mechanisms. Therefore, higher concentrations of IFN-γ stimulates the uptake, processing and transport of dietary antigens by IECs.