[IgG subclasses targeting NC16A domain of BP180 in bullous pemphigoid]

To evaluate the distribution of four IgG subclasses targeting NC16A domain of BP180 in bullous pemphigoid (BP) patients by developing and optimizing a detection method of anti-BP180NC16A IgG subclasses so as to assess its sensitivity and specificity.

Enzyme-linked immunosorbent assay (ELISA) was developed with recombinant GST-BP180NC16A proteins generated by a bacterial expression system. And 136 BP sera and 20 healthy control sera from our hospital between 2009 and 2012 were tested by ELISA, and the cutoff value of four IgG subclasses was set at an A reading corresponding to the mean value plus 3 times of standard deviation of 20 healthy controls sera. Western blot was also used to detect the IgG subclasses in patients with four positive IgG subclasses by ELISA.

The cutoff value of specific IgG1, IgG2, IgG3 and IgG4 were 0.113,0.196,0.154 and 0.120. The values of four IgG subclasses from 20 healthy controls were lower than the corresponding cutoff value, making the detection system good specificity. The positive rates of anti-BP180NC16A IgG1, IgG2, IgG3 and IgG4 antibody were 67.6% (92/136) , 45.6% (62/136), 50.7% (69/136) and 54.4% (74/136) respectively in 136 BP sera. All four IgG subclasses were positive in 29 BP sera, accounting for 21.3%. The number of BP sera positive for at least one IgG subclass were 112, accounting for 82.4%, indicating that the combined sensitivity of four IgG subclasses was 82.4%. Western blot revealed that the number of positivity was 15 and 14 for IgG1 and IgG4 respectively in 20 BP patients with four IgG subclasses positive with ELISA.

The specificity of ELISA is excellent while its sensitivity needs further improvements.