Six important genes for human leukocyte antigens are contributed by each parent. So each person inherits a double set of six major genes that produce six major corresponding antigens, HLA-A, -B, -C, -DP, -DQ, and -DR. Since as many as 20 varieties exist for each of these HLA-producing genes in different individuals, the total possible human leukocyte antigens that can mark "self" and trigger an immune response number about 10,000!
![6 Major Genes: 10,000 Antigens](https://webarchive.library.unt.edu/eot2008/20090117100740im_/http://www.cancer.gov/images/Documents/84790913-8189-4760-83de-6fbad2a812ed/slide12.jpg)
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