Two different Gal-deficient IgA1 myeloma proteins, Mce and Gou (3 and 10 µg/ml final concentration), were added to cord-blood serum (CBS3), or serum from an IgAN patient or a healthy control (2% serum final concentration in the culture medium). After overnight incubation at 4 °C to allow formation of immune complexes, the samples were added to serum-starved human mesangial cells, and cellular proliferation was measured after 20-h incubation. Controls included stimulation with IgA1 proteins alone. Panel (a) shows proliferation with IgA1 proteins without allowing time for immune complex formation in serum samples (no complexes were formed) and panel (b) shows proliferation with IgA1-containing immune complexes. The changes in proliferation are shown as difference in thymidine uptake between a sample and a mock control (mock-treatment with no IgA1 added) (Δcpm). Mean and SD are shown (n = 6).