Autoantibodies against parathyroid hormone in a patient with terminal renal insufficiency

An autoantibody against mid-C-regional, possibly mid-regional, parathyroid hormone was detected in the plasma of a patient with terminal renal insufficiency who was on intermittent haemodialysis. 43-68(Tyr)hPTH and 42-55(Tyr)hPTH were selectively bound by his IgG fraction. 43-68(Tyr)hPTH had the highest affinity for the autoantibody; intact parathyroid hormone did not displace radiolabelled 42-55(Tyr)hPTH or 43-68(Tyr)hPTH. As concentrations of circulating antibodies against mid-C/mid-regional parathyroid hormone fell rises in intact and mid-C-regional parathyroid hormone levels and in alkaline phosphatase activity were observed. This autoantibody directed against the middle portion of the parathyroid hormone molecule seemed to have some protective properties against the osteoblast-stimulating activity of the hormone, implying that the mid-C-region or middle region of the molecule has some biological importance.