Disturbance in the serum IgG subclass distribution in patients with anti-Hu positive paraneoplastic neurological syndromes

Autoantibodies in patients with paraneoplastic neurological syndromes (PNS) have been reported to be predominantly IgG1 and IgG3 isotypes. However, no data are available about the IgG subclass distribution of the total serum IgG in these patients. Therefore, we investigated the IgG subclass distribution (given as percentage of total IgG) in 15 anti-Hu positive PNS patients, 15 patients with small cell lung cancer (SCLC) without PNS and 23 healthy controls using a commercial enzyme-linked immunosorbant assay test. Although IgG1 (and to a lower extent IgG3) are the predominant subclasses of the anti-Hu antibodies, PNS and SCLC showed a significant decrease in IgG1 and a concomitant increase in IgG2 compared with healthy controls (P< 0.05, respectively). In contrast, only SCLC patients, but not PNS patients, had higher IgG3 and IgG4 values compared with controls (P < 0.05, respectively). There was no correlation between IgG subclass levels and the titre or the predominant isotype of the antineuronal antibodies. PNS patients with autonomic disturbances had lower IgG4 levels than PNS patients without autonomic disturbances (P < 0.05). Our study demonstrates a disturbance in the IgG subclass distribution in PNS patients which is partly different from SCLC patients. The isotype regulation of the anti-Hu antibody seems to be independent from this phenomenon.