Rat anti-Mouse Ly-6B.2 Alloatigen monoclonal antibody for FC. Alloimmunity is a condition in which the body gains immunity against antigens of another individual of the same species, which are perceived as foreign. Alloimmunity should not be confused with autoimmunity in which the bodys immune system attacks its own cells without being provoked or influenced by substances or cells from another member of the same species. One alloantigen is known as "Qa-1". If either alloimmunity or autoimmunity is directed against red blood cells (RBCs), the direct Coombs test is positive.