We know that everybody's DNA pattern is different in the world. Then how can ´we transfer blood from one person to another person and this person can survive ?
A few components to my answer.
- Red blood cells do not contain a nucleus, therefore, they do not harbour DNA.
- The major determinant of blood compatibility is the blood antigen. There are only 4 types: O, A, B, AB. This is genetically encoded, and is expressed as a set of sugar coats on the blood cell membrane. However, the enzymes that encode for A or B should be identical from person to person.
I hope this gives you a preliminary answer to work off.
Because one's DNA doesn't have to exactly match another person at all 3 billion locations for the transfusion to be successful. As it turns out, there are only a few proteins that determine whether a person's blood is a match to someone else's. And as it turns out, in the vast majority of the human population, there are only three alleles of the ABO gene, and only two alleles for the Rh gene, and for the vast majority of cases, compatibility of those two proteins is all that you need.
It is critical for you to realize that one's DNA is not the determining factor when it comes to a blood transfusion. Rather, what you have to look at is the proteins being expressed by the DNA coding for blood-associated proteins, as it is these proteins that are the determinant of blood acception or rejection.In other words, the key question is whether or not the blood being transfused harbors antigens -- specific blood proteins associated with a given blood genotype like A & B -- that are foreign to the recipient.
Individuals that have type A blood express A-type antigens, but also house anti-B antibodies which specifically bind to blood with the B antigen. For a person with type A blood (AO or AA), transfusing either AB or A type blood would be dangerous. The RBC in both cases would house B antigens, which the recipient would respond to the transfusion by initiation an immune response against the blood.
I want to touch up one more time on your connection of DNA to rejection of blood. Please be careful with this as different DNA really does not mean much in this case OR in many other biological cases. You have to be much more specific and ask what is the DNA encoding, what is is transcribing and eventually translating and how that relates to the biological process in question. For blood type, although every individual has 'different' DNA, their DNA for blood type has 3 distinct alleles to consider --iO, iA and iB. These alleles are located only within a small region of a person's overall DNA and the difference are 3 discrete categories, as opposed to every person having a different allele and expressing a different protein. If every person different over this small segment of DNA, in the DNA coding for blood type, then indeed it would be possible for each person to make unique antigens and thus for all transfusions to be rejected.
However, since the differences encompass only 3 allele types, people can only have a limited range of genotypes (aO, aa, bo, bb, ab, oo) which connect to only 4 distinct phenotypes (A, B, AB, O). So there is different in DNA, but the difference is defined and limited, so that overlap of genotypes between is possible and compatibility is quite common. So yes people differ in that DNA, but you have to ask if those differences are significant for a particular biological phenomenon.