TOPIC DISCUSSION: Membranous and Class Type IgG

Membranous GN can be idiopathic or secondary. Idiopathic has been associated with IgG4 subtype noted on IF which activates complement alternatively. The secondary forms usually are either IgG1, 2 or 3 and don't activate complement alternate pathway but do classical pathway. When lupus or hepatitis patients have membranous, the IF usually shows IgG1,2 or 3 and possibly full house and TRIs as well( in lupus). The patients with MPGN have granular glomerular deposits of all four IgG subclasses, with a predominance of IgGl and IgG3. These data suggest that the IgG4 subclass may play an important role in the pathogenesis of idiopathic membranous.
Another distinguishing feature at least now available is the antibodies to the human phospholipase
A2 receptor (PLA2R) found in many patients with idiopathic membranous.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576972/pdf/clinexpimmunol00139-0066.pdf
http://www.nephronpower.com/2010/06/topic-discussion-primary-vs-secondary.html