Ovalbumin serves as a neo-transplantation antigen in retinal pigment epithelial cells.

PURPOSE: Our long-term goal is to determine the optimal methods for inducing allograft tolerance to facilitate transplantation of retinal pigment epithelial cells or stem cells for the treatment of retinal degenerative diseases. These goals have been hampered by the extreme complexity of allograft rejection and the heterogeneity of responding T cells. The current studies were undertaken to develop a simplified transplant model for studying rejection and tolerance in the unique environment of the eye. METHODS: To provide a defined transplantation antigen, transgenic C57BL/6 (B6) mice were produced, which express the exogenous chicken egg ovalbumin (OVA) gene under the regulation of the mouse tyrosinase related protein-1 (TRP-1) promoter that is transcriptionally active in retinal pigmented epithelial (RPE) cells. To determine whether the transgene was expressed as a neo-transplantation antigen, RPE from TRP-1-OVA mice were injected into the subretinal space of B6 mice or B6 mice expressing the OVA-specific (OT1) TCR transgenes and examined for inflammatory cell infiltration. RESULTS: The TRP-1-OVA transgenic mice expressed OVA mRNA in the brain and eye but not the heart or kidney. RPE cells from TRP-1-OVA transgenic mice expressed mRNA and protein encoded by the OVA gene and RPE expressing TRP-1-OVA induced an inflammatory response within the subretinal space of OT1 mice but not in B6 mice. CONCLUSIONS: OVA serves as a defined, neo-transplantation antigen in RPE that is recognized by mice whose CD8+ T cells recognize OVA peptide. These observations provide new tools for future studies of the mechanisms of rejection and prolongation of RPE transplants in the eye.

Genetic tagging shows increased frequency and longevity of antigen-presenting, skin-derived dendritic cells in vivo.

Dendritic cells (DCs) are key regulators of immune responses that activate naive antigen-specific T lymphocytes. In draining lymph nodes, antigen-bearing DCs are reported to be rare and short-lived. How such small numbers of short-lived DCs can activate rare antigen-specific T cells is unclear. Here we show that after immunization of mouse skins by gene gun, the number of antigen-bearing DCs that migrate to draining lymph node is 100-fold higher than previously estimated and that they persist for approximately 2 weeks. The substantial frequency and longevity of DCs in situ ensures ample antigen presentation and stimulation for the rare antigen-specific T cells in draining lymph nodes.

Interleukin-12-induced cytotoxicity against syngeneic B cell lymphomas of SJL/J mice.

The B cell lymphomas (RCS) that develop spontaneously in 90% of aging SJL/J mice stimulate syngeneic CD4+ Vbeta16+ Th2 cells to produce cytokines, such as IL-4 and IL-5, which promote lymphoma growth. Although RCS cells express a unique superantigen (vSAg) encoded by an endogenous MMTV (Mtv-29) provirus that also elicits IFN-gamma production from naïve syngeneic lymphoid cells, there is no development of RCS-specific cytotoxicity. However, addition of IL-12 to co-cultures of SJL spleen and irradiated (gamma-)RCS cells resulted in the appearance of effector cells that killed RCS and NK-susceptible target cells. Antibody depletion studies revealed at least two types of RCS/IL-12-induced cytotoxic cells: (1) NK cells (Asialo GM1+) and (2) CD8+ CTL. Despite high titers of IFN-gamma in the SN of co-culture of SJL spleen and gamma-RCS cells, cytotoxicity only developed if IL-12 was also included in the co-cultures. The results of RNAse protection assays and multi-parameter FACS analysis demonstrated an upregulation of IFN-gamma and decrease in IL-4 by activated Th cells in co-cultures with IL-12. These results indicate that inclusion of IL-12 in primary co-cultures of SJL spleen and gamma-RCS cells influences the qualitative nature of the response to favor use of RCS-responsive Th1 rather than Th2 cells to facilitate the production of cytotoxic effector cells. Results of in vivo experiments support this hypothesis, as judged by tumor growth assays and FACS analysis of the tumor cell content of lymphoid tissues. Inhibition of lymphoma growth was observed in mice given gamma-RCS/IL-12-induced effector cells prior to injection of viable RCS cells. These results demonstrate that IL-12 can be used to alter the host immune response leading to induction of cytotoxic effector cells that inhibit the development and/or progressive growth of otherwise resistant B cell lymphomas in SJL/J mice.