noun, plural: alloimmunities
Alloimmunity is a type of immunity that produces an immune response against antigens from members of the same species. An example of this is when the body attacks transplanted tissues resulting in graft rejection.
Alloimmunity results when the products of highly polymorphic genes (e.g. MHC complex genes) of the donor are different from those of the recipient. The immune cells (e.g. T lymphocytes and mononuclear leukocytes) recognize the tissue graft as not-self and attack it. For instance, CD4+ and CD8+ T lymphocytes and Natural Killer cells are associated with cellular rejection of the graft. Another is the participation of B lymphocytes in alloimmunity. These cells are involved in humoral type of rejection. In humoral rejection, B lymphocytes of the recipient produce antibodies that attack the donor's MHC class I and II molecules.1
1 Fang, L., Atz, M. E., and Reed, E. F. (2009), Human leukocyte antigen antibodies in chronic transplant vasculopathy-mechanisms and pathways. Curr Opin Immunol. 21(5): 557–562.