Virology and Microbiology, Center for Biomedical Education and Research (ZBAF), Witten/Herdecke University, 58453 Witten, Germany.
Bavarian Health and Food Safety Authority, 85764 Oberschleißheim, Germany.
Genes (Basel). 2023 Jun 26;14(7):1348. doi: 10.3390/genes14071348.
As the MHC-I-pathway is key to antigen presentation to cytotoxic T-cells and, therefore, recognition by the host adaptive immune system, we hypothesized that SARS-CoV-2 including its Variants of Concern (VOCs), influences MHC-I expression on epithelial cell surfaces as an immune evasion strategy. We conducted an in vitro time course experiment with the human airway epithelial cell line Calu-3 and the human colorectal adenocarcinoma cell line Caco-2. Cells were infected with SARS-CoV-2 strains non-VOC/B.1.1, Alpha/B.1.1.7, Beta/B.1.351, Gamma/P.1, and Delta/B.1.617.2. At 2, 24, 48 and 72 h post-infection we performed RT-qPCR to track viral replication. Simultaneously, we performed intracellular staining with a serum of a double-vaccinated healthy adult containing a high amount of spike protein antibody. In flow cytometry experiments, we differentiated between infected (spike protein positive) and bystander (spike protein negative) cells. To compare their HLA expression levels, cells were stained extracellularly with anti-HLA-A-IgG and anti-HLA-B,C-IgG. While HLA-A expression was stable on infected Calu-3 cells for all variants, it increased to different degrees on bystander cells in samples infected with VOCs Beta, Gamma, Delta, or non-VOC over the time course analyzed. In contrast, HLA-A levels were stable in bystander Calu-3 cells in samples infected with the Alpha variant. The upregulation of MHC-I on spike protein negative bystander cells in Calu-3 cell cultures infected with Beta, Gamma, Delta, and partly non-VOC might suggest that infected cells are still capable of secreting inflammatory cytokines like type-I interferons stimulating the MHC-I expression on bystander cells. In comparison, there was no distinct effect on HLA expression level on Caco-2 cells of any of the VOCs or non-VOC. Further investigations of the full range of immune evasion strategies of SARS-CoV-2 variants are warranted.
作为 MHC-I 途径是将抗原呈递给细胞毒性 T 细胞的关键，因此也是宿主适应性免疫系统识别的关键，我们假设 SARS-CoV-2 及其关注变体 (VOC) 会影响上皮细胞表面的 MHC-I 表达，以此作为一种免疫逃避策略。我们进行了一项体外时间进程实验，使用人呼吸道上皮细胞系 Calu-3 和人结直肠腺癌细胞系 Caco-2。细胞感染非 VOC/B.1.1、Alpha/B.1.1.7、Beta/B.1.351、Gamma/P.1 和 Delta/B.1.617.2 的 SARS-CoV-2 株。在感染后 2、24、48 和 72 小时，我们进行 RT-qPCR 以跟踪病毒复制。同时，我们用含有大量刺突蛋白抗体的双接种健康成年人的血清对细胞进行细胞内染色。在流式细胞术实验中，我们区分了感染（刺突蛋白阳性）和旁观者（刺突蛋白阴性）细胞。为了比较它们的 HLA 表达水平，细胞用抗 HLA-A-IgG 和抗 HLA-B、C-IgG 进行细胞外染色。虽然所有变体的感染 Calu-3 细胞的 HLA-A 表达都稳定，但在分析的时间过程中，感染 VOCs Beta、Gamma、Delta 或非-VOC 的样本中，旁观者细胞的 HLA-A 表达增加到不同程度。相比之下，感染 Alpha 变体的样本中旁观者 Calu-3 细胞的 HLA-A 水平保持稳定。在感染 Beta、Gamma、Delta 和部分非-VOC 的 Calu-3 细胞培养物中，刺突蛋白阴性旁观者细胞的 MHC-I 上调可能表明感染细胞仍能够分泌细胞因子，如 I 型干扰素，刺激旁观者细胞的 MHC-I 表达。相比之下，任何 VOC 或非-VOC 对 Caco-2 细胞 HLA 表达水平都没有明显影响。需要进一步研究 SARS-CoV-2 变体的全范围免疫逃避策略。
