IgA nephropathy (IgAN), characterized by mesangial
IgA1 deposits, is a leading cause of
renal failure worldwide. IgAN pathogenesis involves circulating hypogalactosylated
IgA1 complexed with soluble
IgA Fc receptor I (sCD89) and/or anti-hypogalactosylated-IgA1
autoantibodies, but no specific treatment is available for IgAN. The absence of
IgA1 and CD89 homologs in the mouse has precluded in vivo proof-of-concept studies of specific
therapies targeting
IgA1. However, the α1KI‑CD89Tg mouse model of IgAN, which expresses human
IgA1 and human CD89, allows in vivo testing of recombinant
IgA1 protease (IgA1‑P), a
bacterial protein that selectively cleaves human
IgA1. Mice injected with IgA1‑P (1-10 mg/kg) had
Fc fragments of
IgA1 in both serum and urine, associated with a decrease in IgA1-sCD89 complexes. Levels of mesangial
IgA1 deposits and the binding partners of these deposits (sCD89,
transferrin receptor, and transglutaminase 2) decreased markedly 1 week
after treatment, as did the levels of C3 deposition, CD11b(+) infiltrating cells, and
fibronectin.
Antiprotease antibodies did not significantly alter IgA1‑P activity. Moreover,
hematuria consistently decreased
after treatment. In conclusion, IgA1‑P strongly diminishes human
IgA1 mesangial deposits and reduces
inflammation,
fibrosis, and
hematuria in a mouse IgAN model, and therefore may be a plausible treatment for patients with IgAN.