A2 biology - ImmunityWatch
In the ccea bio textbook it says regarding transplanting tissue 'transplant rejection can also involve the action of B-lymphocytes and antibodies. Eg if the blood of a donor and a recipient is different this can produce an immune response involving antibodies. Normally tissue matching is accurate so rejection by B-lymphocytes in this situation is unlikely to occur'. I understand that in the case of blood donation, b lymphocytes are involved as it is humoral-mediated (body fluid) but I don't understand how B lymphocytes would ever be involved in tissue transplantation as they only react to body fluids and tissue/ organ transplant isn't fluid. Any help appreciated thanks!
Transplants are tricky, because while a lot of antigens are conserved between different individuals, there are some that aren't. When you transplant an organ, you're always going to get some kind of immune reaction unless the organ is from an individual who has very similar genetic makeup. This is because all cells express very polymorphic molecules called HLA molecules (polymorphic means they vary in shape a lot between individuals). So, unless the HLA molecule shape is identical between the individuals, the immune system will recognise these antigens as foreign and will generate an immune response against the tissue. Now, HLA isn't the only molecule that varies between individuals, you also have varying blood groups. These blood groups are determined by your antigens on your RBCs, so if you are blood group A for example, then you have A antigens on your RBCs. But here's the key: these antigens are also on the blood vessels in the transplanted organ. So even when transplanting organs and not blood, the blood groups need to match or else you will generate an immune response against the tissue. And if you're still reading this, then here's a final nugget of nerdy info, there are 2 types of organ rejection (there is a 3rd type but I won't go into it). You have subacute rejection, which is when the organ is literally rejected while the transplant is still happening in the surgical theatre, this is pretty rare and occurs when you have preformed "sensitised" antibodies against the tissue, e.g. if you accidentally transplant a B group organ into a group A recipient, then the group A recipient is going to have anti-B antibodies which will reject the organ. The second type of rejection is acute rejection, which is the most common, and involves an immune response against the HLA molecules mentioned earlier. This involves T and B cells, and is delayed because it takes a little bit of time to generate the antibodies against the transplanted tissue.
Organs contain RBC antigens and HLAs hence why you can get antibodies against them. As your book correctly says, blood group matching rarely goes wrong, so you're not likely to get a subacute reaction due mismatching blood group antigens. Be careful with your understanding of humoral immunity. Humoral immunity doesn't mean that the antibodies only target fluids, it means that antibodies circulate in fluids to reach the tissues. This is different from cell-mediated immunity which involves cell-cell interactions and cell recruitment etc
Hope that helps, soz if it was overcomplicated, I nerded out a little bit because I'm lonely and love immunology so much