Effect of IL-4, type I interferon, and IL-15 on the development and function of virtual memory CD8 T cells

Abstract

Conventional memory T cells typically develop from naïve T cells following exposure to antigenic stimulation and acquisition of memory phenotypes. However, certain CD8 T cells in the thymus, known as innate T cells and "virtual memory (VM) CD8 T cells in the peripheral tissues already exhibit memory-like characteristics such as elevated CD44 expression and rapid cytokine production, even without prior exposure to foreign antigens. This study analyzed the function and development of VM CD8 T cells under the influence of different cytokines. Consistent with previous studies, administration of exogenous IL-4 complexed with anti-IL-4 antibody (IL-4C) led to the generation and expansion of memory-like CD8 T cells, along with an increase in CXCR3 expression in both naïve- and memory-like cells. Thus, the migration of virus-specific and bystander CD8 T cells, including those with a naïve phenotype, was facilitated into the lung during influenza infection. To investigate the effect of type I interferon (IFN), IL-4, and IL-15 on the development of VM CD8 T cell subpopulations, VM cells were divided into four subsets based on Ly6C and Sca-1 expression. The development of these subsets was studied using knockout (KO) mice lacking IFN-α receptor 1 (IFNAR1), IL-4, or IL-15 receptor α (IL-15Rα). The population of Ly6C+ Sca-1+ and Ly6C- Sca-1+ VM CD8 T cells was significantly diminished in the spleen of IFNAR1 KO mice, which were unable to receive type I IFN-stimulated signals, although the total number of splenocytes, CD8 T cells and CD44hi CD49d- VM CD8 T cells were comparable to that of wild-type (WT) mice, due to an increased number of Ly6C- Sca-1- VM cells. Conversely, the proportion of Ly6C+ Sca-1- VM CD8 T cells was partially reduced in IL-4 KO mice, resulting in an overall decrease in the total VM CD8 T cell fraction. Both the Ly6C+ Sca-1- and Ly6C+ Sca-1+ VM CD8 T cell subsets were significantly reduced in the spleen of IL-15Rα KO mice. These findings highlight the differential effects of type I IFN, IL-4, and IL-15 cytokines on the development of distinct subsets of VM CD8 T cells. Bulk RNA sequencing analysis of different CD8 T cell subsets, including naïve cells, true memory cells, and four subsets of VM cells, uncovered distinct gene expression patterns. Ly6C+ VM CD8 T cells were enriched with IL-15 signal-related genes such as Il2rb and Il15ra, as well as memory-related genes like Runx2 and Eomes. However, Ly6C- VM cells, along with true memory CD8 T cells, were enriched cell cycle-related genes. In particular, the expression of the Mst1 gene, known to promote cellular quiescence and survival in type I invariant NKT cells (iNKT1) cells upon IL-15 stimulation, was higher in Ly6C+ VM cells compared with other CD8 T cell subsets. This finding correlated with the increased dependency of Ly6C+ VM cells on IL-15 for their survival. Overall, this study demonstrated the heterogeneity of VM CD8 T cells, and their development was affected differentially by type I IFN, IL-4, and IL-15 cytokines. In addition, the upregulation of CXCR3 on VM CD8 cells facilitated their migration to inflammatory sites.

일반적인 기억 T세포는 항원에 노출시 유도되며 기억세포의 표현형을 갖는다. 그러나 흉선 및 말초기관에서 기억세포의 특징을 갖으면서 사이토카인 분비가 빠르게 나타나는 선천 T세포, 혹은 가상기억 세포라 불리는 CD8 T 세포가 존재함이 확인되었다. 본 논문에서는 여러 사이토카인에 의해 유도되는 가상기억 CD8 T 세포의 기능과 그 발달을 확인하고자 한다. 인터류킨-4 복합체 주입시, 마우스 생체내 가상기억 CD8 T 세포가 유도되며 CXCR3을 높게 발현하여 바이러스에 특이적인 CD8 T세포, 방관자 (Bystander) CD8 T 세포 및 미감작세포의 이동을 용이하게 하였다. 가상기억세포의 발달에 미치는 제 1형 인터페론, 인터류킨-4, 인터류킨-15 의 역할을 확인하기 위하여 가상기억세포를 Ly6C와 Sca-1으로 나누어 각각의 유전자결핍 마우스모델에서 확인하였다. 제1형 인터류킨 결핍 마우스에서는 Sca-1을 발현하는 가상기억 CD8 T 세포가 크게 감소하며 인터류킨-15 결핍모델에서는 Ly6C를 발현하는 가상기억 CD8 T 세포가 줄어들었다. RNA-염기서열분석을 통해 Ly6C를 발현하는 가상기억 CD8 T 세포는 인터류킨-15와 관련된 유전자 (인터류킨-2 수용체 베타, 인터류킨-15 수용체 알파)나 기억세포 관련 유전자 (RUNX2, EOMES) 등을 높게 내는 반면 Ly6C 를 발현하지 않는 가상기억 CD8 T 세포는 세포분열과 관련된 유전자를 높게 발현함을 확인하였고, Mst1역시 Ly6C 발현하는 가상기억 CD8 T세포에서 높게 발현하였다.