Detection of soluble HFE associated with soluble transferrin receptor in human serum

Hereditary hemochromatosis is an autosomal recessive disease, and 80-90% of patients exhibit Cys282Tyr or His63Asp mutations in the HFE gene. HFE, also known as major histocompatibility complex (MHC) class I-like molecule, binds to transferrin receptor 1 (TfR1) and beta 2-microglobulin at the cell surface, forming a complex. Some MHC class I molecules are known to be soluble, raising the possibility that HFE also has a soluble form. However, it is not known whether soluble HFE (sHFE) is present in human serum, and there has been no report on the possible binding between sHFE and soluble TfR (sTfR), which is the fragment of the extracellular domain of TfR I released into the blood. In the present study, we purified an sTfR complex from pooled serum collected from healthy volunteers, showing that the main components of the complex are sTfR and transferrin. We also confirmed the existence of sHFE in this complex. This is the first report on the existence of sHFE in human serum.