Lymphopenia is due to a frameshift mutation in Ghmap5 on rat chromosome 4 and is linked to type I diabetes in the diabetes prone (DP) 1313 rat. The hypothesis that bone marrow derived cells confer the lymphopenia phenotype was tested by reciprocal bone marrow transplantation in 40-day-old lethally irradiated diabetes resistant (DR) congenic DR.(lyllyp) (lymphopenia and diabetes) and DR.(+/+) (no lymphopenia and no diabetes) rats.In two independent series of transplants, all DR.(lyp/lyp) rats (n = 5 and 4) receiving DR. bone marrow retained lymphopenia and developed insulitis (5/5 and 4/4) as well as diabetes in some (2/5 and 3/4). Both DR.(+/+) and DR.(lyp/lyp) rats receiving DR.(+/+) bone marrow cells as well as DR.+/+ rats receiving bone marrow cells showed no lymphopenia or diabetes. In accordance with earlier studies in non-congenic BB rats, the DR.(+/+) rats receiving DR. (lyp/lyp) bone marrow cells recapitulated an intermediary phenotype rather than the +/+ or phenotypes.Our data demonstrate that BBDP rat lymphopenia and diabetes are transferred by bone marrow transplantation to syngeneic DR. lyp/lyp but not DR.(+/+) recipients. The intermediary recapitulation of T cells in recipient DR.(+/-/+/-) rats Suggests that radiation resistant (+/-/+/-) cells, the Gimap5 mutation in bone marrow cells, or both may not Support the development of lymphopenia. (c) 2005 Elsevier Ltd. All rights reserved.

Recognition of antigen by cytotoxic T lymphocytes (CTL) is determined by interaction of both the T cell receptor and its CD8 coreceptor with peptide-major histocompatibility complex (pMHC) class I molecules. We examine the relative roles of these receptors in the activation of human CTL using mutations in MHC class I designed to diminish or abrogate the CD8/pMHC interaction. We use surface plasmon resonance to determine that point mutation of the alpha3 loop of HLA A2 abrogates the CD8/pMHC interaction without affecting the affinity of the T cell receptor/pMHC interaction. Antigen-presenting cells expressing HLA A2 which does not bind to CD8 fail to activate CTL at any peptide concentration. Comparison of CTL activation by targets expressing HLA A2 with normal, abrogated, or diminished CD8/pMHC interaction show that the CD8/pMHC interaction enhances sensitivity to antigen. We determine that the biochemical basis for coreceptor dependence is the activation of the 23-kDa phosphoform of the CD3 zeta chain. In addition, we produce mutant MHC class I multimers that specifically stain but do not activate CTL. These reagents may prove useful in circumventing undesirable activation-related perturbation of intracellular processes when pMHC multimers are used to phenotype antigen-specific CD8+ lymphocytes.

The immune response to HIV-1 in patients who carry human histocompatibility leukocyte antigen (HLA)-B27 is characterized by an immunodominant response to an epitope in p24 gag (amino acids 263-272. KRWIILGLNK). Substitution of lysine (K) or glycine (G) for arginine (R) at HIV-1 gag residue 264 (R264K and R264G) results in epitopes that bind to HLA-B27 poorly We have detected a R264K mutation in four patients carrying HLA-B27. In three of these patients the mutation occurred late, coinciding with disease progression. In another it occurred within 1 yr of infection and was associated with a virus of syncytium-inducing phenotype. In each case, R264K was tightly associated with a leucine to methionine change at residue 268. After the loss of the cytotoxic T lymphocyte (CTL) response to this epitope and in the presence of high viral load, reversion to wild-type sequence was observed. In a fifth patient, a R264G mutation was detected when HIV-1 disease progressed. Its occurrence was associated with a glutamic acid to aspartic acid mutation at residue 260. Phylogenetic analyses indicated that these substitutions emerged under natural selection rather than by genetic drift or linkage. Outgrowth of CTL escape viruses required high viral loads and additional, possibly compensatory, mutations in the gag protein.