Thymic selection and adaptability of cytotoxic T lymphocyte responses in transgenic mice expressing a viral protein in the thymus.

Abstract

SummaryUpon primary challenge with lymphocytic choriomeningitis virus (LCMV), H-2 a (BALB/cByJ) mice mount a cytotoxic T lymphocyte (CTL) response to a single immunodominant domain of the viral nucleoprotein (NP) but no detectable response to the viral glycoprotein (GP). To manipulate this CTL response, the viral NP gene was expressed in the thymus and peripheral T lymphocytes using the murine Thyl.2 promoter. As a result, such Thyl.2-NP (H-2 a) transgenic (tg) mice deleted their high-affinity anti-I_CMV-NP CTL, but generated equal numbers of lower-affinity NP CTL. Further, they made an alternative anti-LCMV-GP CTL response that is not normally found in non-tg mice indicating a hierarchial control of the CTL response. Unlike the H-2 a mice, H-2 b (C57B1/6J) mice normally mount a CTL response to both LCMV-GP and -NP. When the LCMV-NP was expressed using the Thyl.2 promoter in these H-2 b mice, the LCMV-NP-specific CTL response was completely aborted and no CTL to new, alternative viral epitopes were generated. Dilutions of H-2 b or H-2 a NP peptides indicated that 3-4 logs less H-2 b NP peptide was required to sensitize syngeneic target cells for CTL-specific lysis, suggesting that the differing affinities of H-2 b and H-2 a major histocompatibility complex molecules for their peptides likely account for the total removal of NP CTL in the H-2 b mice but only partial removal in H-2 a mice made to express thymic NP. Thymic grafting experiments done with thymi from newborn Thyl.2-NP tg mice show that selection processes studied in this model are of central (thymic) origin and are not caused by Thyl.2-positive LCMV-NP-expressing T lymphocytes in the periphery.

Expression of adenoviral E3 transgenes in β cells prevents autoimmune diabetes

“…Expression of the Ad E3 gene complex in ␤ cells prevents virus-induced IDDM in the presence of an antigen-specific trigger. This occurs without influencing the systemic (splenic) anti-viral (self) immune response (Table 1), which is responsible for initiating ␤ cell destruction in RIP-LCMV single transgenic mice (11,12,14,17). This indicates that regulation takes place locally in the islets of Langerhans.…”

“…Five mice were tested per group and the mean Ϯ1 SE is displayed. All groups of mice generated normal (14,19) levels of anti-LCMV primary CTL, which were measured directly ex vivo on day 7 post-LCMV infection with 1 ϫ 10 5 pfu i.p. Secondary CTL activity in spleens was determined on day 60 after infection, after a 5-6 day in vitro stimulation in the presence of LCMV antigen and antigen-presenting cells as described in Materials and Methods.…”

“…RIP-GP 34-20 (H-2 b ) transgenic mice that express the viral GP only in the ␤ cells of the islets were used as a model for rapid-onset IDDM. For slow-onset IDDM, RIP-NP 25-3 (H-2 b ) transgenic mice that express the viral NP in the pancreas and the thymus, but not in any other tissue, were used (14). Generation and characterization of transgenic mice expressing the Ad E3 region under control of the RIP has been described by Efrat et al (5).…”

“…Tissues taken for histological analysis were fixed in 10% zinc formalin and stained with hematoxylin and eosin. Immunohistochemical studies were carried out on 6-to 10-m freshly frozen cryomicrotome sections (14,16) of the pancreas to detect expression of class I MHC, D b , CD4, and CD8. Primary antibodies were applied for 1 hr.…”

“…Because high-affinity antiviral CTL are deleted, IDDM takes 1 to 6 months to develop, and the time depends on the host MHC haplotype. CTL found in the periphery are of lower affinity (7,14), and both CD4 ϩ and CD8 ϩ lymphocytes are required for development of IDDM. In both models, the initiating LCMV-specific anti-self CTL response is restricted by the D b class I MHC allele (15).…”