H antigen

"H substance" redirects here. The term also historically referred to histamine.

H antigen can refer to one of various types of antigens having diverse biological functions. H antigen is located on the 19th chromosome in humans, and has a variety of functions and definitions as follows:

• Also known as substance H, H antigen is a precursor to each of the ABO blood group antigens, apparently present in all people except those with the Bombay Blood phenotype^[1] (see hh blood group)
• Histocompatibility antigen, a major factor in graft rejection. Even when Major Histocompatibility Complex genotype is perfectly matched, can cause slow rejection of a graft.^[2]
  • major H antigens "encode molecules that present foreign peptides to T cells"^[2]
  • minor H antigens "present polymorphic self peptides to T cells".^[2] Includes, e.g. the H-Y antigen
• a bacterial flagellar antigen^[3]

References

1. Science Of Biogenetics. "Do you Know Bombay Blood Group".
2. Janeway, Charles A. (2001). Immunobiology the immune system health & disease (5. ed.). New York: Garland. ISBN 978-0-8153-3642-6. Retrieved 16 December 2013.
3. Farlex. "antigen". The Free Dictionary. Retrieved 16 December 2013.