Tolerance is overcome in beef insulin‐transgenic mice by activation of low‐affinity autoreactive T cells

Abstract

To gain insight into the factors controlling the maintenance or loss of T cell self tolerance we produced beef insulin (BI)-transgenic BALB/c mice. Transgenic mice express BI under control of the human insulin promoter and secrete physiological amounts of beef insulin. Although these mice are tolerant to BI, as evidenced by the lack of insulin-specific IgG antibody production following intraperitoneal immunization, tolerance is not complete. Footpad immunization results in a weak antigen-specific T cell proliferative response, indicating the presence of self-reactive BI-specific T cell in the periphery. These T cells are functional in vivo, providing support for IgG1, IgG2a, and IgG2b BI-specific antibody production, but require higher higher concentrations of antigen than nontransgenic T cells (both in vivo and following recall responses in vitro) to become activated. In vitro, BI-specific T cell proliferation in BI-transgenic mice can be largely restored by addition of interleukin-2, indicating that a significant component of T cell tolerance is mediated by anergy. To characterize the autoreactive T cells that become activated when tolerance is broken, BI-specific T cell hybridomas were generated from transgenic mice and compared to a panel of hybridomas previously derived from nontransgenic BALB/c mice. The majority of BI-transgenic hybridomas recognized the immunodominant A1-14 beef insulin peptide but with lower avidity than BALB/c hybridomas. Consistent with this, none of the dominant T cell receptor rearrangements found in the BALB/c BI-specific T cell receptor repertoire were found in the transgenic hybridomas. These results indicate that, despite evidence for clonal inactivation of many BI-specific T cells in BI-transgenic mice, loss of tolerance results from activation of low-affinity antigen-specific T cells that appear to have escaped this process.

Characterization of CD8+ T Lymphocytes That Persist After Peripheral Tolerance to a Self Antigen Expressed in the Pancreas

“…This probably reflects the in vitro differences in cytolytic activity observed for these CTL, both as populations and as clones, and demonstrates the principle that expression of greater amounts of peripheral Ag results in a more profoundly tolerized repertoire, as reflected in the lower avidity of CTL from InsHA ϩ/ϩ mice. This correlation has been previously observed in the CD4 ϩ T lymphocyte repertoire of transgenic mice expressing either beef insulin (60) or varying levels of hen egg white lysozyme in vivo (61).…”

Mice with Spontaneous Pancreatic Cancer Naturally Develop MUC-1-Specific CTLs That Eradicate Tumors When Adoptively Transferred

“…Significantly, they have shown that vaccination of insulin-dependent HA mice can activate these low avidity CTLs that are able to reject tumor cells expressing high levels of HA, without destruction of pancreatic islet ␤ cells expressing moderate levels of HA. Studies with other transgenic mouse models expressing model proteins as self Ags have shown that T cells with specificity for self proteins can be demonstrated within the peripheral T cell pool (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43). Often, potentially autoreactive T cells manage to escape deletion by virtue of their lower avidity for self Ag even when the transgene element is present in, or is available to, the thymus (44).…”

Graded Deletion and Virus-Induced Activation of Autoreactive CD4+ T Cells

“…[7][8][9]. Previous studies have provided evidence that thymocytes bearing TCRs with low avidities for self peptides (10,11), or that express low levels of high avidity autoreactive TCRs (and/or low levels of coreceptor molecules; Refs. 12-15), can evade negative selection presumably because their sensitivity for their cognate self peptide is insufficient to trigger negative selection (16).…”