Re: Does different ethnic backgrounds serve a problem for liver transplants?

The important parameters here are for the liver not to have any foreign antigens that the immune 
system will react to, which will lead to rejection. The only way to really avoid this is to transfer a 
liver from a human clone of the patient, or an identical twin. The latter is only slightly more 
probable than the former, so almost all transplants done today are an inexact science and the 
immune system must be suppressed (sometimes for months or even years, by drugs such as 
mycophenolic acid, cyclosporin and prednisolone) in order to limit what is commonly referred to 
as "host-versus-graft" response.

In order to determine how "foreign" another person's liver might look to the recipient's immune 
system, one can estimate this parameter by choosing donors who are "matched" in several 
"histocompatibility genes". The most prominent of these are the MHC ("major histocompatibility 
complex") genes, with the acronym revealing its scientific history of being discovered as factors 
that mediate compatibility between immune systems. These are some of the most variable 
("polymorphic") genes between humans- it's part of what really makes us different from each 
other, but not in any way that can be determined just by looking (skin/hair/eye color etc). 
Without going into the fascinating biology of TCR (T-cell receptor) interactions with MHC, 
already a subject of one Nobel prize (and perhaps more to follow), let us just say that transplant 
surgeons test the MHC of livers from potential donors (often accident victims who may now save 
another's life and have a part of them live on for longer) and try to match their MHC to the 
patient's (host) as closely as possible.

So, with that as background, coming to the "ethnic background" issue. Even though I've been in 
the States for almost 20 years, I grew up in a country (hint: the one with the highest Y 
chromosome diversity in Europe on last count) where people generally did not get singled out by 
arbitrary "ethnic" groups by looks, so it's hard for me to relate. But let me assume that you mean 
a category one checks off in surveys here such as "Caucasian",  "African-American", or "Asian", 
which I always answer with "Other". Well, it may surprise some people that since the 70s 
(Lewontin's theory) it has been widely, though not universally, acknowledged that there is more 
genetic diversity within so-called ethnic groups than between them. We finally got the right 
scientific tools in the 00s (which may later be called the first "post-genomic" decade after we are 
all long gone) to put this to the test, and it has generally held out, some dissenting views 
notwithstanding (for example see: Human genetic diversity: Lewontin's fallacy in BioEssays 
25:798–801, 2003). It's ironic to classify people as "African-American", when we are now fairly 
certain that the ancestors of all modern Asian and European humans also came out of Africa 
about ten thousand generations ago. In the truest sense, we are all Africans. Since there was a 
"bottleneck" during the time of these migrations, one would predict that modern Africans are 
more different from each other genetically than modern Asians or Europeans, and this hypothesis 
has also held true so far. Also, coastal societies tend to be more diverse than mountainous ones, 
for obvious reasons.

To summarize, one's ethnic background need not "serve a problem" for liver transplants as long 
as the host and donor are properly matched.