The construction of a new detector is proposed to extend the capabilities of ALICE in the high transverse momentum (pT) region. This Very High Momentum Particle Identification Detector (VHMPID) ...performs charged hadron identification on a track-by-track basis in the 5 GeV/c < p < 25 GeV/c momentum range and provides ALICE with new opportunities to study parton-medium interactions at LHC energies. The VHMPID covers up to 30% of the ALICE central barrel and presents sufficient acceptance for triggered- and tagged-jet studies, allowing for the first time identified charged hadron measurements in jets. This Letter of Intent summarizes the physics motivations for such a detector as well as its layout and integration into ALICE.
T cells play a critical role in the development of collagen-induced arthritis (CIA). Immunization with heterologous (chick) type II collagen (cII) results in chronic inflammation with progressive ...damage to the joints. The expression of specific MHC Class II alpha beta dimers, including IA super(q), is critical to induction of disease. The alpha chains of IA super(q) and IA super(p) are identical in sequence. The IA super(q) and IA super(p) beta chains differ by only four amino acid residues: 85, 86, 88, and 89. However, mice of the H-2 super(p) haplotype are not susceptible to CIA. To examine the impact of these structural differences in IA molecules on T cell Ag recognition, we studied presentation of cII peptides and denatured cII by APCs obtained from H-2 super(q) and H-2 super(p) mice. We also assessed presentation of ovalbumin, myelin basic protein (MBP), and MBP peptides by these APC populations. H-2 super(q) APCs presented both peptides and proteins to our T cell hybrids. In contrast, APCs obtained from H-2 super(p) mice presented peptides, but were defective in the processing and/or presentation of protein Ags. We then altered pairs of the residues in IA super(q) to those found in IA super(p) using site-directed mutagenesis and transfected these constructs into M 12.C3 B cells. All transfectants were able to present peptides, but those expressing IA super(p) were unable to present protein Ags. The use of transfectants expressing hybrid molecules (residues 85 and 86 from IA super(p), 88 and 89 from IA super(q), or vice versa) allowed us to localize the region responsible for this defect to residues 85 and 86 of the beta chain. The presence of IA super(p) residues (glu and thr versus gly and val in IA super(q)) at these sites severely compromised the capacity for protein presentation. Resistance to CIA in H-2 super(p) haplotype mice may be a reflection of the limited repertoire of epitopes to which these mice can respond relative to susceptible H-2 super(q) mice.
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