ANALYSIS OF GLOMERULI-ELUTED GP330 AUTOANTIBODIES AND OF GP330 ANTIGEN OF HEYMANN NEPHRITIS

Quantity, charge, IgG isotype, Ag reactivity of glomerular gp330 autoa ntibodies (gp330Ab), and the charge of the putative Ag, gp330, were st udied in active Heymann nephritis. Gp330 was anionic with an isoelectr ic point of 4.6. Despite variation in C3 glomerular immunofluorescence staining, C5b-9 staining was seen in all rats. Positive correlation w as seen between glomerular gp330Ab and abnormal 24-h proteinuria (r = 0.637, p = 0.008), which appeared to require a certain threshold level of gp330Ab. Positive correlation was also seen between serum and glom erular gp330Ab at time of death (r = 0.55, p < 0.05). No differences w ere seen in charge, IgG isotypes of glomerular gp330Ab, or reactivity to gp330 by Western analysis in rats with or without abnormal proteinu ria. Comparison of gp330Ab IgG isotypes in immune sera and glomeruli s howed no difference in IgG1 and IgG2a, but IgG2b was significantly low er in glomeruli (p < 0.0001). Conclusions: 1) this is the first docume ntation that gp330 is highly anionic; 2) regardless of the degree of p roteinuria, all immunized rats deposit in their glomeruli a qualitativ ely similar type of gp330Ab (charge, IgG isotype, complement activatio n, gp330 reactivity); 3) despite the highly anionic nature of gp330, a nionic gp330Ab accumulate in glomeruli; and 4) complement activation a ppears to occur in every rat with gp330Ab in glomerulus and developmen t of proteinuria is dependent on a certain threshold level of gp330Ab in the glomerulus which, in turn, correlates with the serum level of g p330Ab.