Immunologic heterogeneity of the folate-binding proteins from chronic myelogenous leukemia cells and myelofibrosis spleen.

An FBP has been purified from the spleen (FBP-S) of a patient with agnogenic myeloid metaplasia and myelofibrosis. This binder is similar to a previously purified protein from CML cells (FBP-L) in its molecular weight and affinity for folate analogues. However, each protein has very little cross-reactivity in specific RIAs for each binder, indicating that there are structural differences which can be detected by the immune system. THe concentration of FBP-L in the serum from normal subjects was 2.0 +/- 0.39 ng/ml (mean +/- S.E.M.) and was significantly elevated in the serum from some patients with CML, uremia, hepatitis, and cancer. The concentration of FBP-S, on the other hand, was 8.31 +/- 0.51 ng/ml in normal serum and remained in this range in the same serum that contained the elevated concentration of FBP-L. In contrast, the concentration of FBP-L was only 13% to 30% of the concentration of FBP-S measured in the homogenates of normal and adjacent cancerous tissue from lungs and colons. These studies indicate that some FBP(s) in human tissues have immunologic specificity even though they are functionally similar.