Immunocytochemical binding of serum IgG from a patient with oat cell tumor and paraneoplastic motoneuron disease to normal human cerebral cortex and molecular layer of the cerebellum.

Serum from a patient with oat cell (OC) tumor and paraneoplastic upper and lower motoneuron syndrome showed binding of IgG but not IgM to normal human cerebral cortex (CC), molecular (M), and Purkinje (P) cell layers of the cerebellum, anterior horn cells (AHC), and dorsal root ganglia (DRG). There was no binding to glial and granular cells, white matter, peripheral nerve, or OC. Sera from three patients with OC tumor without neurologic deficit, three patients with non-OC lung cancer and peripheral neuropathy, and five healthy subjects were used as controls. While none of the control sera showed binding to the CC or M layer, the three controls with OC showed 50% reactivity with AHC, and other controls showed weak staining of PC, AHC, or DRG. Absorption of the patient's serum with cerebral or cerebellar tissue, but not with liver or spinal cord, resulted in elimination of the immunostaining. Staining of the CC and M layer could not be blocked by a monoclonal IgG to a glioma cell line, but partial blocking occurred by preincubating the tissue with monoclonal IgG (MF 491) to gastric carcinoma and cross-reacting with OC and several neural elements. The results suggest specific binding of the patient serum IgG to the CC and M layer; however, the relationship of this antibody to the pathogenesis of the paraneoplastic syndrome remains elusive.