Paraneoplastic anti-Hu serum: studies on human tumor cell lines

Patients with low titers of anti-Hu, the paraneoplastic encephalomyelitis/sensory neuronopathy (PEM/PSN) antibody, have a better tumor prognosis that those who do not harbor these antibodies. Accordingly, we examined the effects of serum from patients with anti-Hu antibodies on human tumor cell lines, in order to determine: (1) if the serum was toxic (growth inhibition or cytolysis) to tumor cells with or without complement, and (2) if anti-Hu antibodies contributed to tumor toxicity. The serum of 14 patients with anti-Hu associated PEM/PSN, 22 patients with small-cell lung cancer (SCLC) without anti-Hu antibodies, and 20 normal individuals were studied. Three cell lines (NT-2, BE(2)-C, and SH.SY5Y) that express Hu proteins, and one cell line (SAOS-2) that does not, were studied. We examined the effects of whole serum, IgG-depleted serum, and purified IgG in the presence or absence of complement. A higher percentage of anti-Hu sera were toxic (71%) compared with sera from anti-Hu negative SCLC patients (23%) (p < 0.0001). No correlation existed between the titer of anti-Hu antibodies and toxicity. The toxic effects were observed in all tumor cell lines including the cell line that does not express Hu antigens. Toxicity persisted in serum depleted of IgG. Purified anti-Hu IgG in the presence and absence of complement, was not toxic. Our findings indicate that anti-Hu serum is toxic for human tumor cell lines, but this toxicity does not appear to be mediated by anti-Hu antibodies.