allogenic
Meaning of allogenic: A variant spelling of a transplant term, describing tissue from another person and therefore tissue the immune system can tell apart.
Definition of allogenic
Allogenic describes cells, tissue or an organ taken from one individual and given to a genetically different individual of the same species. It is a variant spelling of allogeneic, which is the form standard in transplant medicine and laboratory work. The genetic difference is the whole point of the word, because it is what lets the recipient's immune system recognize the graft as foreign.
How does it compare with the related terms?
| Term | Source of the tissue | Immune consequence |
|---|---|---|
| Autologous | The same person | No rejection |
| Syngeneic | An identical twin | No rejection |
| Allogeneic | Another person | Rejection and graft-versus-host disease possible |
| Xenogeneic | Another species | Immediate and severe rejection |
Same species is not the same thing as genetically identical, and that is where short definitions of this word usually go wrong. An identical twin is the same species, yet tissue passing from one twin to the other behaves as though it came from the recipient, and it is called syngeneic rather than allogeneic for exactly that reason.
Why does the genetic difference matter so much?
Every cell displays a set of surface proteins working as an identity badge, inherited in combinations so numerous that two unrelated people rarely match. Immune cells patrol for badges that are not their own. In a transplanted organ, the recipient's immune cells attack the graft, which is rejection. In a marrow or stem cell graft the traffic runs the other way as well, because immune cells arriving inside the graft attack the recipient, a reaction called graft-versus-host disease. Matching donor to recipient on those badges reduces both, and drugs that suppress immunity restrain what matching cannot prevent.
Which spelling is correct?
Allogeneic is the standard form in medicine, and it appears in the names of procedures such as allogeneic bone marrow transplantation. Allogenic is a shortened variant, common enough to persist in older records, on product labels and in some laboratory writing, and identical in meaning. The shorter spelling also carries a wholly unrelated sense in geology, describing rock material that originated somewhere else, so searching on it alone returns a mixture.
Also known as
Used in a sentence
The patient proceeded to an allogenic stem cell transplant from a matched sibling.
Good to know
Same species does not mean genetically identical, so tissue exchanged between identical twins is syngeneic rather than allogenic, and it is the genetic difference that produces rejection and graft-versus-host disease.
Word origin
Where “allogenic” comes from
Allo- comes from the Greek allos, meaning other, and the ending traces to the Greek genos, meaning origin or kind.