High-titer/low-avidity antibodies

High titer, low avidity antibodies are usually alloantibodies to antigens which are present in low numbers on red blood cells and are thus weakly reactive. These antigens include: residual HLA antigens, Chido and Rodgers (located on the complement protein C4), and the Knops blood system which includes York (Yka), Knops (Kna and Knb), and McCoy (McCa and McCb) (located on complement receptor type 1). The majority of the red cell antigens to which HTLAs are formed are present at high frequency in the population. These antibodies usually do not cause increased red cell destruction when incompatible blood is transfused or hemolytic disease of the fetus and newborn, although rare case reports of acute hemolytic transfusion reactions are present in the literature (Hoppe et al., Vox Sanguinis (2002), 82: 207-210).