HFE is a protein known to be involved in iron metabolism; yet, other than its homology with major histocompatibility complex (MHC) class I molecules, it has not been described as having an immunologic function. Here we report that peripheral blood mononuclear cells (PBMCs) from patients with hereditary hemochromatosis (HH) carrying the C282Y mutation in HFE have reduced cell-surface expression of MHC class I due to an enhanced endocytosis rate of MHC class I molecules caused by premature peptide and ␤ 2 -microglobulin dissociation. This faster turnover also leads to increased expression levels of cell-surface free class I heavy chains in mutant PBMCs. Biochemical analysis indicates an earlier peptide loading and endoplasmic reticulum maturation of MHC class I molecules in C282Y mutant cells. Thermostability assays further showed that in HFE mutants the MHC class I peptide loading gives rise to low-stability heterotrimers that dissociate prematurely during its intracellular traffic. The present results suggest the existence of an intriguing cross-talk between a particular HFE mutation and the classical MHC class I route. These findings constitute the first description of peptide presentation pathway abnormalities linked to HFE and provide additional evidence for the occurrence of immunologic defects in patients with HH. IntroductionAntigenic peptides presented by major histocompatibility complex (MHC) class I molecules to CD8 ϩ T cells are mainly derived from proteolysis of newly synthesized proteins in the cytosol 1-3 by the proteasome and TPPII (tripeptidyl-peptidase II). 4 A heterodimer of 2 membrane-spanning molecules, termed TAP1 (transport associated with antigen processing 1) and TAP2, translocates the peptides to the lumen of the endoplasmic reticulum (ER) [5][6][7][8] where they undergo further trimming of their amino-terminal ends by the aminopeptidase ERAAP (aminopeptidase associated with antigen processing in the ER). 9,10 Loading of peptides onto MHC class I molecules involves the formation of a transient protein complex termed the peptide-loading complex (PLC) 11,12 that facilitates the binding of peptide to MHC-␤ 2 -microglobulin (␤ 2 -m) heterodimers. 11 The conformational changes that occur in the newly formed peptide-loaded MHC class I molecules precede their release from the PLC and subsequent delivery to the cell surface via the standard secretory pathway.MHC class I assembly and export from the ER is a complex process 13,14 subjected to a set of quality control mechanisms. This orchestrated process acts concertedly to ensure that high-affinity peptides are loaded onto class I molecules. Tapasin, calreticulin, and ERp57 are some of the key players supposed to take part in this event. 15 Yet the precise mechanisms responsible for optimization of class I maturation and for the prevention of ER escape of premature class I molecules remain to be fully understood.Here, we have studied assembly, peptide loading, and surface expression of MHC class I molecules in peripheral blood mononuclear cells (...

Background: It has been recently demonstrated that CD8+ T-lymphocyte numbers are genetically transmitted in association with the MHC class I region. The present study was designed with the objective of narrowing the region associated with the setting of CD8+ T-lymphocyte numbers in a population of C282Y homozygous hemochromatosis subjects, in whom a high prevalence of abnormally low CD8+ T-lymphocyte counts has been described.

HFE was discovered as the hereditary hemochromatosis (HH) gene. It is located on chromosome 6 (6p21.3), 4Mb telomeric to the HLA-A locus, and its product has a structure similar to MHC class I molecules. HFE encodes two frequent mutations: C282Y and H63D. One of these (C282Y) is present in a large proportion of Caucasian HH patients. HFE has a tissue distribution compatible with a role in iron absorption (intestine), recycling (macrophages) and transport to the fetus (placenta).

the results of the present study reinforce that the procedures used to determine the individual abilities and inabilities were useful in planning the intervention procedures.

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The major histocompatibility complex (MHC) shows a remarkable conservation of particular HLA antigens and haplotypes in linkage disequilibrium in most human populations, suggesting the existence of a convergent evolution. A recent example of such conservation is the association of particular HLA haplotypes with the HFE mutations. With the objective of exploring the significance of that association, the present paper offers an analysis of the linkage disequilibrium between HLA alleles or haplotypes and the HFE mutations in a Portuguese population. Allele and haplotype associations between HLA and HFE mutations were first reviewed in a population of 43 hemochromatosis families. The results confirmed the linkage disequilibrium of the HLA haplotype HLA-A3-B7 and the HLA-A29 allele, respectively, with the HFE mutations C282Y and H63D. In order to extend the study of the linkage disequilibrium between H63D and the HLA-A29-containing haplotypes in a normal, random population, an additional sample of 398 haplotypes was analyzed. The results reveal significant linkage disequilibrium between the H63D mutation and all HLA-A29-containing haplotypes, favoring the hypothesis of a co-selection of H63D and the HLA-A29 allele itself. An insight into the biological significance of this association is given by the finding of significantly higher CD8 + T-lymphocyte counts in subjects simultaneously carrying the H63D mutation and the HLA-A29 allele.

An earlier study of reference values of iron parameters in Portugal showed significant differences between populations from northern and southern villages. This study addresses the question of the geographical distribution in Portugal of the two main mutations (C282Y and H63D) of the hereditary hemochromatosis gene, HFE. For that purpose, a stratified sample of 640 anonymous dried blood spot samples was randomly selected from the major regions of Portugal: North, Center, Lisbon and the Tagus Valley, Alentejo and Algarve. Differences in the geographical distribution of these two mutations were observed thus confirming the presumed differences between the age of the two mutations which is compatible with the postulated Celtic/Nordic origin of the C282Y mutation. The finding of a significantly higher allelic frequency of the C282Y mutation in the North (0.058) than in the South (0.009) could also point to an effect of differential selective forces acting in the different geographical areas of the country. Data on archaeological, ethnographic and linguistic records and on the North/South distribution of Portuguese cattle breeds of European or African origin have also been reported. In addition to their interest for population genetics, the results represent a reminder of the need to take into account regional differences in the design of strategies for population screening of hereditary hemochromatosis. European Journal of Human Genetics (2001) 9, 843 ± 848.

To identify a new marker of expression of disease, independent of HFE genotype in patients with hereditary haemochromatosis (HHC), the total peripheral blood lymphocyte counts were analysed according to iron status in two groups of subjects with HFE mutations. The groups consisted of 38 homozygotes for C282Y, and 107 heterozygotes for the C282Y or compound heterozygotes for C282Y and H63D. For control purposes, totallymphocyte counts and iron status were also examined in 20 index patients with African dietary iron overload, a condition not associated with HFE mutations, and in 144 members of their families and communities. Mean lymphocyte numbers were lower in C282Y homozygous HHC index subjects with cirrhosis and higher iron stores than in those without cirrhosis and with lower iron burdens [(1.65 +/-0.43) x 10(6)/mL vs. (2.27 +/-0.49) x 10(6)/mL; p = 0.008]. Similarly, mean lymphocyte counts were significantly lower in C282Y heterozygotes and C282Y/H63D compound heterozygotes with iron overload and increased serum ferritin concentrations compared to those with normal serum ferritin concentrations (p < 0.05). Statistically significant negative correlations were found, in males, between lymphocyte counts and the total body iron stores, either in C282Y homozygous HHC patients (p = 0.031 in a multiple regression model dependent on age) and in C282Y heterozygotes or C282Y/H63D compound heterozygotes with iron overload (p = 0.029 in a simple linear model). In contrast, lymphocyte counts increased with increasing serum ferritin concentrations among the index subjects with African iron overload (r = 0.324, not statistically significant) and among the members of their families and communities (r = 0.170, p = 0.042). These results suggest that a lower peripheral blood lymphocyte count is associated with a greater degree ofiron loading in HFE haemochromatosis but not in African iron overload, and they support the notion that the lymphocyte count may serve as a marker of a non-HFE gene that influences the clinical expression of HFE haemochromatosis.