Pattern of epitopic reactivity of the anti-Hu antibody on HuD with and without paraneoplastic syndrome

Previous study has shown that the anti-Hu antibody titre of serum samples from patients with paraneoplastic encephalomyelitis/paraneoplastic sensory neuronopathy (PEM/PSN) was significantly higher than that from patients with small cell lung cancer without neurological disturbances (non-PEM/PSN). The aims of this study were (1) to identify the fine epitopes on HuD recognised by the anti-Hu antibody, (2) to determine if the pattern of epitopic reactivity differed between antibodies from patients with and without PEM/PSN, and (3) to determine if the pattern of epitopic reactivity correlated with the clinical features. Recombinant full length HuD and nine deletion fragments were constructed and immuno-reacted by western blot analysis with 14 anti-Hu serum samples from eight patients with PEM/PSN and six without PEM/PSN. All anti-Hu serum samples reacted with the deletion fragments containing amino acids (aa) 90-101 or aa 171-206. Some anti-Hu samples reacted with the deletion fragments containing aa 223-234, aa 235-252, or aa 354-373. There was no difference in the pattern of epitopic reactivity between patients with and without PEM/PSN. There was no correlation between the pattern of epitopic reactivity and the clinical features. The anti-Hu antibody titre from patients with PEM/PSN was significantly higher than from patients without PEM/PSN, but there was overlap of their titre concentrations. In conclusion, aa 90-101 and aa 171-206 are the major epitopes with which all anti-Hu serum samples react, and aa 223-234, aa 235-252, and aa 354-373 are the minor epitopes with which only some anti-Hu serum samples react. The analyses suggested that the pattern of epitopic reactivity of the anti-Hu antibody on HuD was not a critical factor for the development or clinical features of PEM/PSN.