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Regulation of immune responses and autoimmunity by activating and inhibitory NK receptors expressed by T lymphocytes: role of ITAM versus ITIM signal balance


Immune cell activity is regulated by both activating and inhibitory receptors, which transduce signals through two motifs: ITAM and ITIM, respectively. ITIM receptors play a key role in the regulation of ITAM induced activation of leukocytes, thus creating a balance, which regulates cellular functions and the outcome of the immune response (immune priming or tolerance).

Moreover aberrant expression of activating and/or inhibitory immune receptors and of their ligands can lead to deleterious effects, including autoimmunity. While inhibitory NK receptors are also often expressed by normal T cells, the activating counterparts are mostly found on pathogenic self reactive T cells in autoimmune diseases.

Transgenic mice expressing activating receptor Ly49D/DAP12 an d/or its inhibitory counterpart Ly49A (in presence/absence of H 2Dd as ligand) offer the opportunity to better understand the role of ITAM/ITIM balance in T cell biology, and the relevance of T cell ITAM signalling (via DAP12) in autoimmunity.

We first pro pose to address T lymphocyte differentiation in Ly49D/DAP12 transgenic mice, by studying thymocyte development and TCR repertoire selection. Peripheral T lymphocyte function will be investigated upon Ly49D engagement alone or in combination with TCR stimulation.

With the aim to assess the function of activating receptors expressed by CD8+ T cells in autoimmunity, a model of diabetes will be used (RIP-LCMV mice). The CD8+ T cells of the Ly49D/DAP12 transgenic mice will be will be transferred into RIP LCMV G P transgenic mice, whose beta islet cells express LCMV GP (lymphocytic choriomeningitis glycoprotein) as self antigen.

In this model, self-reactive CD8+ T cells trigger diabetes only upon adequate stimulation (e.g. LMCV infection, CD28/B7.2 costimulation). We will test whether ITAM signalling via Ly49D/DAP12 is sufficient to trigger diabetes. Consequently this approach might allow bringing new insight in autoimmunity to design novel appropriate treatments.

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