Immune deviation of 2C transgenic intraepithelial lymphocytes in antigen-bearing hosts

The present study examined self-tolerance for T cell receptor (TCR)αβ intestinal intraepithelial lymphocytes (iIELs) using the 2C transgenic (Tg) mouse model specific for a peptide antigen (Ag) presented by the class I major histocompatibility complex H-2L(d). Although Tg⁺ T cells were largely deleted from the periphery of Ag⁺ mice, equivalent numbers of Tg iIELs were present in Ag⁺ compared to Ag^- mice. Tg iIELs in Ag^- mice contained CD8αβ, CD8αα, and CD4⁺CD8⁺ subsets, whereas only CD8αα and CD4^- CD8^- Tg iIEL subsets were detected in Ag⁺ mice. Analysis of surface markers revealed that Tg iIELs in Ag⁺ mice expressed decreased levels of Thy-1 and increased CD45R/B220 as compared to Ag^- Tg iIELs. In response to activation with exogenous peptide or immobilized anti-TCR mAb, iIELs from Ag^- mice proliferated at high levels and produced interleukin (IL)-2 and interferon (IFN)-γ, while Tg⁺ iIELs from Ag⁺ mice proliferated at low levels and failed to produce detectable IL-2 or IFN-γ. Activation of sorted iIEL subsets from Ag mice revealed that CD8αα and CD4^-CD8^- subsets produced low levels of IL-2 and IFN-γ in response to activation with antigen- presenting cells and added peptide or immobilized anti-TCR mAb, while CD8αβ⁺ iIELs responded to endogenous levels of peptide. In response to APC and exogenous peptide, sorted iIEL subsets from Ag⁺ mice produced IL-2 and IFN-γ, and proliferated at greatly reduced levels compared to corresponding subsets from Ag mice. Analysis of cytokine mRNA levels revealed that activation in vitro induced IL-2 mRNA only in Ag^-, but not Ag⁺ iIELs, whereas a high level of IL-4 mRNA reduction was detected in Tg⁺ iIELs from Ag⁺ mice, and to a lesser degree, from Ag^- mice. These data suggest that tolerance for Tg⁺ iIELs resulted in the deletion of CD8αβ⁺ subsets and the persistence of Tg⁺ iIEL subsets with decreased sensitivity to endogenous levels of self-peptide. A comparison of the cytokine profiles expressed by Tg⁺ iIEL subsets in Ag^- and Ag⁺ mice suggested that tolerance induction had involved the functional deviation of cells from TC1 (T helper-1-like) to a less inflammatory TC2 (T helper-2-like) phenotype capable of mediating humoral immune responses in the mucosa.