しずいちゃん

Signs of yourself = HLA.

Perhaps you know your blood type. The type which must be matched when you get blood transfusion. But, beside this A-B-O blood types, doctors found that tissues transplanted from other people are frequently rejected by immune system of patients. The reason was mismatch of human leucocyte antigens (HLAs). There are so many types HLAs and for successful transplantation these HLAs must be matched.

In our body, these HLAs are functioning to detect virus infection and abnormal growth of cancer cells. The variation of HLAs was evolved to prevent extinction by a single lethal virus.

And this defence system is so sensitive and also functioning to distiguish others' tissues and cells from ours.