An unusual case of autoimmune agranulocytosis with total absence of myeloid precursors: demonstration of diverse sources of R binder for cobalamin in plasma and secretions.

An unusual autoimmune agranulocytosis featured intense plasmacytosis, hyperglobulinemia, and total absence of myeloid precursors. Remission was induced with prednisone and cyclophosphamide on two separate occasions, producing reversal of all the above abnormalities. Anti-granulocyte antibodies were demonstrated in relapse by staphylococcal protein A assay. During agranulocytosis, levels of the R binder for cobalamin in the blood were greatly diminished (20-60 pg/mL unsaturated binding capacity). Moreover, the acquired R binder deficiency was accompanied by the previously undescribed phenomenon of a shift of endogenous serum cobalamin to transcobalamin II; only 10-19% of endogenous cobalamin was attached to R binder. In remission, unsaturated R binder rose to normal levels and R binder also carried 78-91% of endogenous cobalamin. This confirms that granulocytes are responsible for most of the circulating R binder in humans. In contrast, salivary R binder concentration was normal throughout the patient's course, indicating that secretory R binder is nongranulocytic in origin. These data establish that R binder has more than one source in humans.