No abstract

No abstract

Human mannan-binding protein (MBP) is a serum lectin participating in the innate immune defence. Low MBP concentrations are explained by the dominant action of a point mutation at codon 54 of the MBP gene in Eskimos, partially in Caucasians, but not in Africans. A previously described point mutation at codon 57 was very frequent (0.23) in East Africans, low in Caucasians (0.02), and absent in Eskimos. The African population only conformed to Hardy-Weinberg expectation when assuming the existence of an unknown allele, which was subsequently found as a point mutation at codon 52. This allele appeared with a relatively high frequency (0.05) in both Africans and Caucasians, but was absent in Eskimos. Hardy-Weinberg equilibrium is now seen in the investigated ethnic groups. All cases of MBP deficiency may be explained by these three variants.

The multiple sclerosis (MS)-associated HLA major histocompatibility complex (MHC) class II alleles DRB1*1501, DRB5*0101 and DQB1*0602 are in strong linkage disequilibrium, making it difficult to determine which is the principal MS risk gene. Here we show that together the DRB1 and DRB5 loci may influence susceptibility to MS. We demonstrate that a T cell receptor (TCR) from an MS patient recognized both a DRB1*1501-restricted myelin basic protein (MBP) and DRB5*0101-restricted Epstein-Barr virus (EBV) peptide. Crystal structure determination of the DRB5*0101-EBV peptide complex revealed a marked degree of structural equivalence to the DRB1*1501-MBP peptide complex at the surface presented for TCR recognition. This provides structural evidence for molecular mimicry involving HLA molecules. The structural details suggest an explanation for the preponderance of MHC class II associations in HLA-associated diseases.

Mannose-binding lectin (MBL) is a key factor in innate immunity, and lung infections are the leading cause of morbidity and mortality in cystic fibrosis (CF). Accordingly, we investigated whether MBL variant alleles, which are associated with recurrent infections, might be risk factors for CF patients. In 149 CF patients, different MBL genotypes were compared with respect to lung function, microbiology, and survival to end-stage CF (death or lung transplantation). The lung function was significantly reduced in carriers of MBL variant alleles when compared with normal homozygotes. The negative impact of variant alleles on lung function was especially confined to patients with chronic Pseudomonas aeruginosa infection. Burkholderia cepacia infection was significantly more frequent in carriers of variant alleles than in homozygotes. The risk of end-stage CF among carriers of variant alleles increased 3-fold, and the survival time decreased over a 10-year follow-up period. Moreover, by using a modified life table analysis, we estimated that the predicted age of survival was reduced by 8 years in variant allele carriers when compared with normal homozygotes. Presence of MBL variant alleles is therefore associated with poor prognosis and early death in patients with CF.

A major aim of HLA and disease association studies is to identify the causative HLA factor truly responsible for the association. This is usually difficult due to the pronounced linkage disequilibrium between most HLA determinants. The causative factor must show the strongest association compared to all other factors. Here we describe a simple analysis which can be used to identify which of two factors, say A and B, shows the strongest association. The basic data for the analysis are the entries of the two-by-four table giving the four phenotypic combinations of A and B in patients and controls, respectively. These data are analyzed in various two-by-two tables involving stratification of each of the two factors against the other. A stronger increase of factor A is established if A is significantly associated with the condition both in B-positives and in B-negatives, when this is not true for B in A-positives and A-negatives. Using simulation with control data, it is demonstrated how linkage disequilibrium may influence secondary associations. The analysis may also be used to investigate interaction between HLA factors, but linkage disequilibrium complicates the interpretation in such cases. The method is exemplified using various published data. Finally, some statistical recommendations are given. Thus, we advise that phenotype (marker) frequencies are generally used instead of gene (i.e. allele, or haplotype) frequencies. The importance of correcting p-values, the levels of significance, and the power of Fisher's exact test are discussed.

No abstract

MHC class II (MHC-II) molecules play a central role in the selection of the T cell repertoire, in the establishment and regulation of the adaptive immune response, and in autoimmune deviation. We have generated knockout mice lacking all four of the classical murine MHC-II genes (MHCII ⌬͞⌬ mice), via a large (80-kilobase) deletion of the entire class II region that was engineered by homologous recombination and Cre recombinase-mediated excision. These mice feature immune system perturbations like those of A␣ and A␤ knockout animals, notably a dearth of CD4 ؉ lymphocytes in the thymus and spleen. No new anatomical or physiological abnormalities were observed in MHCII ⌬͞⌬ mice. Because these animals are devoid of all classical MHC-II chains, even unpaired chains, they make excellent recipients for MHC-II transgenes from other species, avoiding the problem of interspecies cross-pairing of MHC-II chains. Therefore, they should be invaluable for engineering ''humanized'' mouse models of human MHC-II-associated autoimmune disorders.