Immune Mechanisms
In vivo model lacking cross-presentation: functionally selective suicide of CD8+ dendritic cells
ML Lin, Y Zhan, AM Lew in collaboration with AI Proietto, S Prato, L Wu, WR Heath, JA Villadangos (Immunology Division) Pub ref: 90
Cross-presentation as a fundamental pathway of activating CD8+ T cells has been well established; however the mechanisms that specialise CD8+ dendritic cells (DC) for this task are not fully understood. Here, we take advantage of the specific cytosolic export feature of cross-presenting DC together with the property of cytosolic cytochrome c (cytc) in initiating Apaf-1-dependent apoptosis selectively in cross-presenting DC. A single intravenous injection of cytc in mice produced a 2-fold reduction in splenic CD8+ DC in wild-type but not Apaf-1 deficient mice. Functional studies both showed that cytc profoundly abrogated antigen-specific CD8+ T cell proliferation through its apoptosis-inducing effect on cross-presenting DC. More importantly, in vivo injection of cytc abolished the induction of cytotoxic T lymphocytes (CTL) to exogenous antigen and reduced subsequent immunity to tumour challenge. In addition, only the proportion of CD8+ DC that express abundant IL-12 and TLR3 were efficient cross-presenters. Our data support the hypothesis that cross-presentation in vivo requires cytosolic diversion of endocytosed proteins, conferring cross-presentation specialisation to a proportion of CD8+ DC. We propose that DC incapable of such transfer, even within the CD8+ DC subset, are unable to cross-present. Our model opens an avenue to manipulate CTL responses toward infections, tumors and transplants by specifically targeting cross-presenting DC.
Horse cytc-mediated apoptosis of cross-presenting DC. FACS of splenic DC 24h after injection with 5mg of horse or yeast cytc. Note that yeast cytc binds poorly to Apaf-1 so is not apoptogenic. Numbers indicate the relative % of surface marker+ cells. Results are typical of over 10 experiments with 3-5 mice/group.
GITR expression is reciprocally regulated by NF-κB and NFAT
Y Zhan, E Coghill, D Bourges, YK Xu, JL Brady, AM Lew in collaboration with S Gerondakis (The Burnet Institute of Medical Research)
Although Foxp3 regulates glucocorticoid-induced TNF receptor (Gitr) expression in the T regulatory cells, little is known about how Gitr is transcriptionally regulated in conventional T cells. A genetic dissection of Gitr transcriptional control revealed that of the three transcription factors downstream of the classical NF-κB pathway (RelA, cRel and NF-κB1), RelA is a critical positive regulator of Gitr expression. In contrast, NFAT acts as a negative regulator of Gitr expression under certain conditions. This was evidenced by our findings that agents suppressing NFAT activity enhanced TCR-mediated Gitr expression, whereas agents enhancing NFAT activity suppressed TCR-mediated Gitr upregulation.