The charge selectivity (CS) function in human renal disease has not been unequivocally demonstrated to date. However, the clearance ratio of
IgA to
IgG may be theoretically useful in estimating CS in humans, since
IgA and
IgG have similar sizes and tertiary structures, but distinct isoelectric points (3.5-5.5 [
IgA] and 4.5-9.0 [
IgG]), and Stokes-Einstein radius: 61 A (
IgA) and 49-60 A (
IgG). Two-dimensional electrophoresis with the following immunoblotting revealed that the considerably anionic portion (isoelectric points [pI] <4.0) of
IgA, visible in serum, was absent in the urine in
steroid-sensitive nephrotic syndrome (SSNS) but present in the same during
IgA nephropathy (IgAN) and
membranoproliferative glomerulonephritis (MPGN). A
latex assay revealed the CS index (CSI) was significantly low in patients with podocyte disease (group A), including SSNS, focal and
segmental glomerulosclerosis (FSGS) and Finnish-type congenital
nephrotic syndrome (FCNS), but high in those with
Alport syndrome (AS), IgAN, Henoch-Schönlein
purpura nephritis (HSPN), and MPGN (group B). The linear regression analysis of the
IgA size selectivity index (
IgA SSI; clearance ratio of
IgA to
transferrin) and SSI (clearance ratio of
IgG to
transferrin), which represents the clearance ratio of
IgA to
IgG referring to the
transferrin clearance, revealed the influence of the charge more accurately. Indeed, the slope of the regression lines of
IgA SSI (y) to SSI (x) were concluded to be y = 0.39x (group A) and y = 1.05x (group B), respectively. These results suggested that the charge selective barrier among podocyte diseases (group A) is preserved to some degree, but lost in cases of
nephritis and AS (group B).