No abstract

The molecular basis of hereditary complement factor I deficiency is described in two pedigrees. In one pedigree, there were two factor I-deficient siblings, one of whom was asymptomatic and the other suffered from recurrent pyogenic infections. Their factor I mRNA was analyzed by reverse transcription of fibroblast RNA followed by amplification using the polymerase chain reaction. Both siblings were homozygous for the same transversion (adenine to thymine) at nucleotide 1282 in the cDNA. This mutation causes histidine-400 to be replaced by leucine. The altered histidine is a semi-conserved residue within the serine proteinase family, although no function has been ascribed to it. The proband of the second pedigree studied was found to be a compound heterozygote. One allele had the same mutation as the first family, the second allele had a donor splice site mutation that resulted in the deletion of the mRNA encoded in the fifth exon (a low-density lipoprotein receptor domain) from its transcript. ( J. Clin. Invest. 1996. 97:925-933.)

The potential suppressive effects of allospecific anergic T cells were investigated both in vitro and in vivo. Allospecific T cells were rendered unresponsive in vitro using immobilized anti-CD3 mAb. These anergic T cells profoundly inhibited proliferation of responsive T cells in an antigen-specific manner. The observed inhibition did not appear to be due to the release of inhibitory cytokines in that secretion of IL-2, IFN-gamma, IL-4, IL-10 and TGF-beta was greatly reduced following the induction of anergy, and neutralizing mAb specific for IL-4, IL-10 and TGF-beta failed to reverse the inhibition. Furthermore, the suppression mediated by anergic T cells required cell to cell contact. In vivo, adoptive transfer of anergic T cells into recipients of allogeneic skin grafts led to prolonged skin graft survival. Consistent with the lack of inhibitory cytokine production by the anergic cells, prolongation of skin allograft rejection was not influenced by the simultaneous administration of a neutralizing anti-IL-4 antibody. These results indicate that anergic T cells can function as antigen-specific suppressor cells both in vitro and in vivo.

This study provides the first evidence that Foxp3-transduced T cells can control the rejection of an allogeneic transplant and suggests that T-cell Foxp3 gene transfer may have therapeutic value in clinical transplantation.

The immunogenic properties of primary cultures of murine lung microvascular endothelial cells (EC) were analyzed. Resting endothelial cells were found to constitutively express low levels of MHC class I and CD80 molecules. IFN-γ treatment of EC resulted in a marked up-regulation of MHC class I, but no change was observed in the level of CD80 expression. No CD86 molecules were detectable under either condition. The ability of peptide-pulsed EC to induce the proliferation of either the HY-specific, H2-Kk-restricted CD8+ T cell clone (C6) or C6 TCR-transgenic naive CD8+ T cells was analyzed. Resting T cells were stimulated to divide by quiescent peptide-prepulsed EC, while peptide-pulsed, cytokine-activated EC lost the ability to induce T cell division. Furthermore, Ag presentation by cytokine-activated EC induced CD8+ T cell hyporesponsiveness. The immunogenicity of activated EC could be restored by adding nonsaturating concentrations of anti-H2-Kk Ab in the presence of an optimal concentration of cognate peptide. This is consistent with the suggestion that the ratio of TCR engagement to costimulation determines the outcome of T cell recognition. In contrast, activated peptide-pulsed EC were killed more efficiently by fully differentiated effector CD8+ T cells. Finally, evidence is provided that Ag recognition of EC can profoundly affect the transendothelial migration of CD8+ T cells. Taken together, these results suggest that EC immunogenicity is regulated in a manner that contributes to peripheral tolerance.

The bias of αβ T cells for MHC ligands has been proposed to be intrinsic to the T-cell receptor (TCR). Equally, the CD4 and CD8 coreceptors contribute to ligand restriction by colocalizing Lck with the TCR when MHC ligands are engaged. To determine the importance of intrinsic ligand bias, the germ-line TCR complementarity determining regions were extensively diversified in vivo. We show that engagement with MHC ligands during thymocyte selection and peripheral T-cell activation imposes remarkably little constraint over TCR structure. Such versatility is more consistent with an opportunist, rather than a predetermined, mode of interface formation. This hypothesis was experimentally confirmed by expressing a hybrid TCR containing TCR-γ chain germ-line complementarity determining regions, which engaged efficiently with MHC ligands. MHC restriction | TCRT cells expressing an αβ T-cell receptor (TCR) are MHCrestricted, recognizing self-and foreign peptide epitopes presented by MHC class I and II molecules during thymic development and peripheral activation, respectively. Two mechanisms are proposed to underlie this ligand bias. First, the CD8 and CD4 coreceptors have dual specificity for extracellular MHC and the intracellular proximal kinase Lck. Consequently, when MHC class I or II ligands are engaged, Lck is colocalized with the TCR/CD3 complex initiating signal transduction. The importance of this mechanism in disadvantaging non-MHC ligands is highlighted by the recovery of T-cell selection, where MHC and the coreceptors are both absent in comparison to the absence of MHC alone (1). In this setting, non-MHC ligands drive thymic positive selection and are recognized by peripheral T cells (2). The ability of αβ TCRs to recognize non-MHC ligands does not rule out an intrinsic bias of the TCR for MHC ligands. Indeed, evidence for such a hardwired bias is suggested by pairwise interactions between TCR-β germ-line complementarity determining regions 1 and 2 (CDR1/2) and the MHC α-helices observed in several structures (3-7). Recently, such recurrent interactions have been shown to be dependent on the partner TCR-α chain, which can impose distinct modes of TCR-β engagement, suggesting they may not drive MHC specificity (8). Although the relatively limited set of TCR/MHCpeptide structures reveals a semiconserved docking geometry, the angle of TCR engagement varies by more than 60°and the generally central docking position can shift toward the peptide aminoor carboxy-terminus (9). Likewise, conserved features of the MHC α-helices, including exposure of the polypeptide backbone and surface depressions, have been suggested to provide energetically favorable sites for CDR engagement (5). However, a crucial role for specific MHC residues in TCR docking has not emerged (10). The role of germ-line TCR structure in the bias to MHC ligands has thus been perplexing, especially given the structural variability of both components. To investigate this, we have applied a unique mutagenesis approach based on redirecting V(D)J recombina...

Thyroid autoimmune disorders comprise more than 30% of all organ-specific autoimmune diseases and are characterized by autoantibodies and infiltrating T cells. The pathologic role of infiltrating T cells is not well defined. To address this issue, we generated transgenic mice expressing a human T-cell receptor derived from the thyroid-infiltrating T cell of a patient with thyroiditis and specific for a cryptic thyroid-peroxidase epitope. Here we show that mouse major histocompatibility complex molecules sustain selection and activation of the transgenic T cells, as coexpression of histocompatibility leukocyte antigen molecules was not needed. Furthermore, the transgenic T cells had an activated phenotype in vivo, and mice spontaneously developed destructive thyroiditis with histological, clinical and hormonal signs comparable with human autoimmune hypothyroidism. These results highlight the pathogenic role of human T cells specific for cryptic self epitopes. This new 'humanized' model will provide a unique tool to investigate how human pathogenic self-reactive T cells initiate autoimmune diseases and to determine how autoimmunity can be modulated in vivo.

How positive selection molds the T cell repertoire has been difficult to examine. In this study, we use TCR-β-transgenic mice in which MHC shapes TCR-α use. Differential AV segment use is directly related to the constraints placed on the composition of the CDR3 loops. Where these constraints are low, efficient selection of αβ pairs follows. This mode of selection preferentially uses favored AV-AJ rearrangements and promotes diversity. Increased constraint on the α CDR3 loops leads to inefficient selection associated with uncommon recombination events and limited diversity. Further, the two modes of selection favor alternate sets of AJ segments. We discuss the relevance of these findings to the imprint of self-MHC restriction and peripheral T cell activation.