Killer cell receptors: keeping pace with MHC class I evolution.

NK cells express receptors that bind to polymorphic determinants of MHC class I heavy chains. MHC ligands vary greatly between mammalian species, and the use of distinct molecular families of NK cell receptors by humans and mice suggests that the receptors too can be evolving rapidly. The KIR (killer cell inhibitory receptor) family of receptors are found in primates and recognize class I epitopes that are of relatively recent origin in primate evolution. Therefore, KIR molecules have probably evolved class I receptor function more recently than C-type lectins, which are represented in both humans and mice. Individual humans express NK cell receptors for which they have no class I ligand, demonstrating a looseness in the coupling of expression between the receptors and their ligands. However, study of a single donor suggests that every NK cell expresses at least one inhibitory receptor for a self-HLA class I allotype, consistent with the missing self hypothesis. Thus the NK-cell receptor-class I interaction appears to control the NK-cell repertoire during ontogeny of the individual and has the potential to be a selective factor influencing both MHC class I and NK cell receptor diversity in the evolution of populations and species.

Stable inheritance of an HLA-"blank" phenotype associated with a structural mutation in the HLA-A*0301 gene.

A serological family study identified an HLA-A "blank" segregating through three generations of apparently healthy individuals. The HLA-A*0301 allele was assigned by DNA genotyping in each of the three individuals. Complete absence of cellular expression of the HLA-A3 antigen was associated with a 6 nucleotide deletion in exon 3 of the A*0301 gene. The in-frame deletion of nucleotides 373-378 results in the absence of residues C101 and D102 from the mature HLA-A heavy chain. Cysteine 101 is involved in the formation of the highly conserved disulfide bridge in the alpha 2 domain of the class I molecule, and deletion of this residue is believed to be highly disruptive to proper folding and function of the class I molecule.

Evolution of MHC class I genes in higher primates.

The classical major histocompatibility complex (MHC) class I genes are conserved in higher primates. Motifs common to human, chimpanzee and gorilla alleles indicate that class I alleles diverged from ancestral sequences that existed before separation of these species. Analysis of native human populations such as Australian Aborigines and Amerindians shows that HLA-B is characterized by rapid generation of new alleles. HLA-A and -C appear to be evolving more slowly. Comparison of alleles for orthologous class I genes in humans and other primates confirms that similar mechanisms contribute to the generation of new alleles in these species.

HLA class I variation in Australian aborigines: characterization of allele B*1521.

Traditional methods of serological typing have largely used antisera of Caucasoid origin, which can overlook HLA heterogeneity in non-Caucasoid populations. Therefore, we have used molecular techniques to evaluate potential polymorphism in HLA class I molecules of Aborigines from the central desert and northern coast of Australia. The DNA sequence of common Aboriginal HLA-A and B antigens were compared with serological reaction patterns which suggested new polymorphisms. Although serological data indicated that long and short variants of A34 may exist, regardless of the serological pattern, all individuals carried the A*3401 allele. Therefore, the variation in A34 reaction pattern observed serologically was not attributable to primary sequence variation in the HLA A*3401 allele. Similarly, there was no detectable polymorphism in the sequences of selected HLA-B alleles, even though some of these alleles showed unusual serological reaction patterns. However, a new allele of B15 (B*1521) was detected in two individuals carrying this serotype. The cells from both of these individuals showed ambiguous reaction patterns with monospecific B62 and B75 sera. cDNA sequencing of the HLA B15 gene from these cells revealed a B15 allele that differed from B*1502 by a single nucleotide change. This change occurred at position 272, resulting in a C to G substitution at residue 67 in the consensus B15 cDNA sequence. Hence, the Australian Aborigines as an ethnic group show very little primary sequence polymorphism within the class I loci, consistent with the results obtained from previous serological studies.

HLA DPB1 genotyping in Australian aborigines by amplified fragment length polymorphism analysis.

The HLA-DPB1 alleles in 93 Australian aborigines, from two geographically separate areas within Australia, were studied by AFLP analysis. There was a restricted range of DPB1 alleles seen in the aboriginal population, and the distribution of alleles varied between the two aboriginal groups. DPB1*0501 was the most common allele in the aborigines from the Central Desert, whereas DPB1*0401 was the most frequent allele in the Northern Coast aborigines. A new AFLP pattern was observed, and was found to correspond to the allele DPB1*2201, recently identified by SSO analysis. The DPB1 allele frequency distribution for both of the aboriginal groups was different from that seen for the Australian Caucasoid population.

Analysis of mixed human/microbial DNA samples: a validation study of two PCR AMP-FLP typing methods.

The reliability of the PCR technique used to type two human variable number tandem repeats, that is, 3' to apolipoprotein B gene and locus D17S30, was examined using DNA samples of mixed human and microbial origin. Mixtures of human and microbial DNA were amplified, choosing microbes found commonly in the vagina. Total inhibition of human amplification and/or "drop-out" of the larger amplification fragment length polymorphism allele was observed at both loci in the presence of DNA from some vaginal micro-flora.