FYN and nephritis: To examine whether Fyn-mediated inhibitory SHP-1S591 phosphorylation were associated with immune complex-mediated disease via the FcγRIIA in patients with a given inflammatory disease, we analyzed blood leukocytes from untreated patients with lupus nephritis at different stages of renal involvement morphologically classified as class IV-A (severe nephritis with immune deposits and leukocyte infiltration) and pure class V (membranous immune deposits only).