Serum immunoglobulin G level in patients with lupus nephritis and the effect of treatment with corticosteroids and mycophenolate mofetil

Background: Reduced serum IgG level is associated with increased risk of infection. We investigated the circulating IgG level and its determining factors in active lupus nephritis patients treated with corticosteroids and mycophenolate mofetil (MMF).

Methods: This was a retrospective study on the longitudinal IgG profile in Class III/IV ± V lupus nephritis patients treated with prednisolone and MMF.

Results: 46 patients were included. At baseline, 34 (73.9%) patients (Group I) had normal or elevated IgG (1444.0 ± 600.5 mg/dL) while 12 (26.1%) (Group II) had IgG levels (567.8 ± 160.9 mg/dL) below the lower limit of normal. IgG levels at baseline, three, six and 12 months after treatment were 1215.4 ± 649.7 mg/dL, 843.9 ± 347.6 mg/dL, 914.5 ± 362.4 mg/dL and 1034.6 ± 452.5 mg/dL respectively. Treatment with prednisolone and MMF led to a significant drop in IgG after two weeks, reaching a nadir at eight weeks, followed by gradual normalization. Similar changes in IgG were observed in Group I patients but there was non-significant change in Group II within the first 24 weeks. Eighteen (39.1%) patients had low IgG by six months, and only one patient had IgG <300 mg/dL, at both three and six months. IgG level was negatively associated with proteinuria at six months (r = -0.711, p = 0.010). Five of 18 patients with low IgG had infections within the first year, while IgG levels below the lower limit of normal did not increase infection risk (relative risk 1.863; 95% confidence interval 0.466 to 6.818, p = 0.280).

Conclusion: Reduced IgG occurred in 26% of active lupus nephritis patients and the IgG levels are significantly influenced by the severity of proteinuria. Treatment with prednisolone and MMF does not result in clinically important suppression of IgG.