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Background. BALB/c mice control infection with the obligate intracellular parasite Toxoplasma gondii and develop a latent chronic infection in the brain, as do immunocompetent humans. Interferon-γ-producing CD8+ T cells provide essential protection against T. gondii infection, but the epitopes recognized have so far remained elusive. Methods. We employed caged major histocompatibility complex molecules to generate ~ 250 H-2Ld tetramers and to distinguish T. gondii-specific CD8+ T cells in BALB/c mice. Results. We identified 2 T. gondii-specific H-2Ld-restricted T cell epitopes, one from dense granule protein GRA4 and the other from rhoptry protein ROP7. H-2Ld/GRA4 reactive T cells from multiple organ sources predominated 2 weeks after infection, while the reactivity of the H-2Ld/ROP7 T cells peaked 6-8 weeks after infection. BALB/c animals infected with T. gondii mutants defective in establishing a chronic infection showed altered levels of antigenspecific T cells, depending on the T. gondii mutant used. Conclusions. Our results shed light on the identity and the parasite stage-specificity of 2 CD8+ T cell epitopes recognized in the acute and chronic phase of infection with T. gondii. [ABSTRACT FROM AUTHOR]

DEP (for Disheveled, EGL-10, Pleckstrin) homology domains are present in numerous signaling proteins, including many in the nervous system, but their function remains mostly elusive. We report that the DEP domain of a photoreceptor-specific signaling protein, RGS9 (for regulator of G-protein signaling 9), plays an essential role in RGS9 delivery to the intracellular compartment of its functioning, the rod outer segment. We generated a transgenic mouse in which RGS9 was replaced by its mutant lacking the DEP domain. We then used a combination of the quantitative technique of serial tangential sectioning-Western blotting with electrophysiological recordings to demonstrate that mutant RGS9 is expressed in rods in the normal amount but is completely excluded from the outer segments. The delivery of RGS9 to rod outer segments is likely to be mediated by the DEP domain interaction with a transmembrane protein, R9AP (for RGS9 anchoring protein), known to anchor RGS9 on the surface of photoreceptor membranes and to potentiate RGS9 catalytic activity. We show that both of these functions are also abolished as the result of the DEP domain deletion. These findings indicate that a novel function of the DEP domain is to target a signaling protein to a specific compartment of a highly polarized neuron. Interestingly, sequence analysis of R9AP reveals the presence of a conserved R-SNARE (for soluble N-ethylmaleimide-sensitive factor attachment protein receptor) motif and a predicted overall structural homology with SNARE proteins involved in vesicular trafficking and fusion. This presents the possibility that DEP domains might serve to target various DEP-containing proteins to the sites of their intracellular action via interactions with the members of extended SNARE protein family. [ABSTRACT FROM AUTHOR]