Re:The really amazing thing (Score 1)

Here's another haematologist answering. I will echo what has been said in a thread above that having two forms of DNA inside you is no big deal now - this is true for almost everyone with a transplant and actually is also true, to a more minor extent, in ex-pregant women who continue to carry trace amounts of foetal cells for the rest of their lives. You are right to say that immune systems don't generally detect foreign DNA - although it is able to detect specific forms of DNA, such as unmethylated CpG motifs that occur in bacteria but not humans or dsRNA that occur in viruses. However, it is set up to detect proteins in the form of peptides 'presented' on the surface of major histocompatibility complex (MHC) proteins, which are what gives us our 'tissue type'. This is why different MHC proteins ie different tissue types provoke such strong immune responses=rejection. Even if the tissue types are shared between donor and recipient, there will be numerous differences between two individuals ( about 0.1% of amino acids). However, most of these differences don't provoke strong reactions. It is now recognised that both self and non-self proteins are recognised. Self proteins provoke active tolerance. Non-self ones don't initially, but will do so if recognised for a sufficient length of time without causing any trouble or 'danger'. Only a small minority of differences cause rejection from the off, but these minor histocompatibility antigens are the cause of many of the rejection episodes. Obviously, the more the differences the higher the likelihood of these differenes occurring. For instance, trans-racial transplants are often disastrous. I think I'll finish there - this is a very complex topic.