Summary
- Lymphoid "antigens" became an experimental artifact of medical techniques (i.e., of transplantation). Simply, as scientist gained familiarity with the human immune system they learned more about graft rejection, the cause was antibody production to proteins in donor tissue. The key word is allo - which means of different origin. 'Allo'typic proteins in 'allo'grafts developed immune responses in recipients. What makes these proteins different?
- From a more modern perspective, HLA gene products (i.e., antigen-presenting, cell-surface receptors) did not evolve to be transplantation antigens, nor to interfere with transplantation, organ transplantation being unknown until 1960. The HLA genes are much older. Variation in HLA major antigens is the cause of transplant rejection, but variation at HLA is under preservative selection (Called heterozygous selection or balancing selection). Variation of HLA has led to an estimate that they are at least 60 million years in age for humans (DRB1). In humans, the number of HLA alleles is expanding, even with many genes, many more are still tolerable as immune presentation antigens.
The scientific problem has been to explain the natural function of a molecule, such as a self cell-surface receptor involved in immunity. It also seeks to explain how variation developed (perhaps by evolutionary pressure), and how the genetic mechanisms works (dominant, codominant, semidominant, or recessive; purifying selection or balancing selection).
Read more about this topic: History And Naming Of Human Leukocyte Antigens
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