H AND B HUMAN BLOOD-GROUP ANTIGEN EXPRESSION IN COCHLEAR HAIR-CELLS IS MODULATED BY THYROXINE

The presence of human blood-group antigens in developing and adult hyp othyroid rat cochleas was analyzed using antibodies directed against a ntigens H and B. During postnatal development, hypothyroid rat cochlea s exhibited a highly selective expression of both B and H antigens, ma inly at the hair cell level. Labeling for antigen B was found througho ut the hair cells, whereas the antibody directed against antigen H sel ectively labeled the apical part of these cells. These immunostaining patterns were similar to those found in normal (euthyroid) rat cochlea s, but antigenic expression periods were clearly prolonged. Thus, wher eas in nor mal rat cochleas, the B and H antigenic expression disappea rs from postnatal day (PD) 9 on, in cochleas of hypothyroid rats the r eactivity was intense until PD15; it decreased from this developmental stage, and was negative or only faintly positive at PD30. Therefore, in congenital hypothyroidism, hair cell immunoreactivity is present at developmental stages that are negative in normal rat cochleas. These results suggest that human blood-group antigen expression on the devel oping cochlear hair cells of rats is modulated by thyroxine and that t hyroxine is necessary for the temporal expression pattern and, secreti on of normal glycoproteins.