The vitamin B12-binding protein in human leukocytes

Markedly Increased Vitamin B12 Concentrations Attributable to IgG–IgM–Vitamin B12 Immune Complexes

“…c BSA, bovine serum albumin. myeloproliferative disorders, and hypereosinophilic syndrome, none of these were present in our patient (3)(4)(5)(6)(7)(8)(9)(10)(11). These clinical conditions are characterized by high myeloid cell mass and turnover associated with maturation (21,22 ).…”

“…Vitamin B 12 in serum is bound to 2 proteins, transcobalamin (TC) 3 II and haptocorrin (HC). TC is a 43-kDa nonglycosylated serum protein that is synthesized primarily in the enterocytes and is essential for the transport of vitamin B 12 from ileum into the blood and then into most cells via receptor-mediated endocytosis (1,2 ).…”

“…High serum vitamin B 12 concentrations frequently occur with myeloproliferative disorders, hypereosinophilic syndromes, and hepatic diseases (3)(4)(5)(6)(7)(8)(9)(10)(11). In these cases, high serum vitamin B 12 concentrations may be caused by up-regulation of HC and TC synthesis, increased release of cellular vitamin B 12 from the liver, or decreased clearance of cobalamin from plasma (12 ).…”

STUDIES ON THE PLASMA PROTEIN BINDING OF [58Co]‐VITAMIN B12

“…They considered that a disintegration product from mature neutrophils contributed to the increased vitamin B12 binding capacity of serum in myeloproliferative disease. However, it was not until 1964 that the presence of a vitamin B12 binding protein in white cells was demonstrated (Simons, 1964;Simons and Weber, 1966). It has been postulated recently (Retief, Cottlieb, Kochwa, Pratt and Herbert, 1967) that leucocytes may be the source of vitamin B12 binding a and fS globulins, and that the myeloid leukaemic granulocyte may give rise to more of the vitamin B12 binding a globulin and less of the j8 globulin than is dehvered into the normal serum by normal granulocytes.…”

“…While no satisfactory explanation has been advanced for these phenomena so far, the possible implication of white cells has been under consideration for some years (Thomas and Anderson, 1956;Fahey, McCoy and Goulian, 1958;Mendelsohn, Watkin, Horbett and Fahey, 1958;Kidd and Thomas, 1962;Meyer, Cronkite, Miller, Mulzac and Jones, 1962;Simons, 1964;Simons and Weber, 1966).…”