Binding of the apo and holo forms of the serum vitamin D-binding protein to human lymphocyte cytoplasm and membrane by indirect immunofluorescence.

The indirect immunofluorescence method is used to study the binding of the serum vitamin D carrier protein (DBP) to lymphocytes. It is shown that in vitro this serum protein will bind to the lymphocyte cytoplasm and intact membrane. This result is in agreement with recent evidence of an actin-binding protein present in the serum. Besides, a difference in the binding to the lymphocyte membrane is observed between the holo forms of the DBP with the different vitamin D derivatives. These findings could be relevant in illuminating the possible role of the DBP in the cellular metabolism of the active metabolites of vitamin D and in the cellular mobility.