T cell receptor Vβ gene expression in monozygotic twins: Discordance in CD8 subset and in disease states

The peripheral T cell repertoire is shaped by positive and negative selection. These intrathymic events are dependent on the direct interaction of MHC and TCR molecules. Inasmuch as one possible mechanism for HLA-linked disease involves the role that these molecules play in shaping the peripheral T cell repertoire, an understanding of how stable the repertoire remains is an important question that will influence future studies. The purpose of this study was to analyze the stability of the T cell repertoire in monozygotic twins. To investigate this question the percentage of CD4 and CD8 T cells expressing TCR Vβ gene products was determined for seven sets of healthy monozygotic twins ages 2 through 44. Vβ expression was determined by three- color flow cytometric analysis using antibodies to Vβ-5.1, -5.2, -5.3, - 6.7, -8, and -12. The percentage of CD4 cells expressing each Vβ gene was highly concordant between twins. In contrast, differences were noted for Vβ expression within the CD8 subset. This was especially marked when sets of twins were studied (n = 3) where one individual had an underlying disease. Although expression in the CD4 subset was again concordant, significant differences were noted within the CD8 subset compared to the healthy twin. These data indicate that in both health and disease, the CD4 T cell repertoire is tightly regulated although often sizable differences have developed in the CD8 compartment.