The Major Histocompatibility Complex of Old World Camels-A Synopsis.

This study brings new information on major histocompatibility complex (MHC) class III sub-region genes in Old World camels and integrates current knowledge of the MHC region into a comprehensive overview for Old World camels. Out of the MHC class III genes characterized, TNFA and the LY6 gene family showed high levels of conservation, characteristic for MHC class III loci in general. For comparison, an MHC class II gene TAP1, not coding for antigen presenting molecules but functionally related to MHC antigen presenting functions was studied. TAP1 had many SNPs, even higher than the MHC class I and II genes encoding antigen presenting molecules. Based on this knowledge and using new camel genomic resources, we constructed an improved genomic map of the entire MHC region of Old World camels. The MHC class III sub-region shows a standard organization similar to that of pig or cattle. The overall genomic structure of the camel MHC is more similar to pig MHC than to cattle MHC. This conclusion is supported by differences in the organization of the MHC class II sub-region, absence of functional DY genes, different organization of MIC genes in the MHC class I sub-region, and generally closer evolutionary relationships of camel and porcine MHC gene sequences analyzed so far.

The major histocompatibility complex of Old World camelids: Class I and class I-related genes.

The genomic structure of the Major Histocompatibility Complex (MHC) region and variation in selected MHC class I related genes in Old World camels, Camelus bactrianus and Camelus dromedaries were studied. The overall genomic organization of the camel MHC region follows a general pattern observed in other mammalian species and individual MHC loci appear to be well conserved. Selected MHC class I genes B-67 and BL3-7 exhibited unexpectedly low variability, even when compared to other camel MHC class I related genes MR1 and MICA. Interspecific SNP and allele sharing are relatively common, and frequencies of heterozygotes are usually low. Such a low variation in a genomic region generally considered as one of the most polymorphic in vertebrate genomes is unusual. Evolutionary relationships between MHC class I related genes and their counterparts from other species seem to be rather complex. Often, they do not follow the general evolutionary history of the species concerned. Close evolutionary relationships of individual MHC class I loci between camels, humans and dogs were observed. Based on the results of this study and on our data on MHC class II genes, the extent and the pattern of polymorphism of the MHC region of Old World camelids differed from most mammalian groups studied so far. Camels thus seem to be an important model for our understanding of the role of genetic diversity in immune functions, especially in the context of unique features of their immunoglobulin and T-cell receptor genes.