Figure 4.

Anti–LAMP-2 antibodies in ANCA-negative patients bind specifically to human glomerular endothelium. (A) Sera from ANCA-negative/hLAMP-2–positive (patients A, C, and D) patients, but not ANCA-positive/hLAMP-2–negative (patient P) patients, bind specifically to glomeruli with a predominantly endothelial pattern in 4-μm unfixed frozen sections of normal human kidney (upper) and to conditionally immortalized human GEnC, which results in a mixed lysosomal and surface staining pattern (lower). The slightly granular linear IgG staining of glomeruli in tissue sections with patient A’s serum is identical to that obtained with the mAb to hLAMP-2 (H4B4) (B) and both patient sera and H4B4 give similar surface staining on ldlD cells stably expressing hLAMP-2 in the plasma membrane (C). Preincubating the antibodies with increasing concentrations of immune-purified native glomerular hLAMP-2 results in complete inhibition of antibody binding at 4.4 ng/μl (B and C inhibited).