Gene expression changes in long-term culture of T-cell clones: genomic effects of chronic antigenic stress in aging and immunosenescence

Abstract

The adaptive immune response requires waves of T-cell clonal expansion on contact with altered self and contraction after elimination of antigen. In the case of persisting antigen, as occurs for example in cytomegalovirus or Epstein-Barr virus infection, this critical process can become dysregulated and responding T-cells enter into a dysfunctional senescent state. Longitudinal studies suggest that the presence of increased numbers of such T-cells is a poor prognostic factor for survival in the very elderly. Understanding the nature of the defects in these T-cells might facilitate intervention to improve immunity in the elderly. The process of clonal expansion under chronic antigenic stress can be modelled in vitro using continuously cultured T-cells. Here, we have used cDNA array technology to investigate differences in gene expression in a set of five different T-cell clones at early, middle and late passage in culture. Differentially expressed genes were confirmed by real-time polymerase chain reaction, and relationships between these assessed using Ingenuity Systems evidence-based association analysis. Several genes and chemokines related to induction of apoptosis and signal transduction pathways regulated by transforming growth factor beta (TGFbeta), epidermal growth factor (EGF), fos and beta-catenin were altered in late compared to early passage cells. These pathways and affected genes may play a significant role in driving the cellular senescent phenotype and warrant further investigation as potential biomarkers of aging and senescence. These genes may additionally provide targets for intervention.

Fig. 1

Network of genes differentially expressed in T-cell clone (TCC) immunosenescence. Forty-three genes that were differentially regulated in late passage, senescent, TCCs were analysed by the Ingenuity Pathway Analysis (IPA) tool. The network shown was significantly associated with cellular movement, haematological system development and function, immune response, cell-to-cell signaling and interaction, and cellular growth and proliferation (P < 0.01). Shaded genes were identified by microarray analysis as differentially expressed in TCC senescence. Other nodal genes are directly or indirectly associated with the differentially expressed genes. The meaning of the nodal shapes is indicated.