CIRCULATING ANTIBODY TO TRANSCOBALAMIN-II CAUSING RETENTION OF VITAMIN-B12 IN BLOOD

  • 1 January 1977
    • journal article
    • research article
    • Vol. 49  (6) , 987-1000
Abstract
A patient with recurrent pulmonary abscess, weight loss and alcoholism had extremely high serum vitamin B12 and unsaturated vitamin B12-binding capacity (UBBC) levels. While transcobalamin (TC) II was also increased, most of his UBBC was due to an abnormal binding protein which carried > 80% of the endogenous vitamin B12 and was not found in his saliva, granulocytes or urine. This protein was a complex of TC II and a circulating Ig (IgG.kappa. and IgG.lambda.). Each IgG molecule appeared to bind 2 TC II molecules. The reacting site did not interfere with the ability of TC II to bind vitamin B12, but did interfere with its ability to transfer the vitamin to cells in vitro. The site was not identical to that reacting with anti-human TC II antibody produced in rabbits. Becuase of this abnormal complex, 57Co-vitamin B12 injected i.v. was cleared slowly by the patient. No metabolic evidence for vitamin B12 deficiency was demonstrable, although the patient initially had megaloblastic anemia apparently due to folate deficiency. The course of the vitamin B12-binding abnormalities was followed over 4 yr and appeared to fluctuate with the status of the patient''s illness. The IgG-TC II complex resembled one induced in some patients with pernicious anemia by intensive treatment with long-acting vitamin B12 preparations. The mechanism of induction of the antibody formation in our patient is unknown.