A novel CSF-1 binding factor in a patient in complete remission following cytotoxic therapy for lymphoma

A novel colony stimulating factor-1 (CSF-1) binding factor present in the serum from a patient in remission from lymphoma is described. Radioimmunoassay (RIA) repeatedly failed to detect circulating levels of CSF-1 in the peripheral blood system of this patient. Molecular analysis showed a normal CSF-1 gene structure by Southern blot analysis and a 46,XX karyotype by cytogenetic analysis. CSF-1 mRNA expression in peripheral blood leucocytes was confirmed using reverse transcriptase polymerase chain reaction analysis. Morphological analysis of bone marrow cells was normal and peripheral blood progenitor cell colony assays showed a pattern of growth within the normal range in response to CSF-1 alone and in combination with other cytokines. Analysis of the patient's plasma and conditioned media prepared from peripheral blood mononuclear and granulocytic cell fractions for their ability to bind 125Iodine-labelled CSF-1 revealed the presence of a plasma CSF-1 binding factor. This binding factor was not present in the patient's urine, because CSF-1 was detected by RIA and production of the binding factor by the patients peripheral blood white cells could not be demonstrated in vitro. To our knowledge, this is the first reported case of a soluble CSF-1 binding factor.