Background/Aims: Patients with IgA nephropathy (IgA-N) are thought to have immune system disorders that frequently result in high serum IgA levels and a relatively high susceptibility to upper respiratory infections. Aims: To clarify the influence of the specific immune response of IgA-N patients on the clinicopathological features of the disease, we measured the whole-blood-producing capacity of interferon-α (IFNα-PC). We then compared these findings with clinical and histopathological parameters, including tissue macrophage infiltration, during both histologically active and latent phases. Patients and Methods: Fifty-one inpatients with IgA-N and 70 healthy controls were examined. According to the histological findings, 32 patients had disease in the active phase (AP), and 19 were in the latent phase (LP). Results: In AP patients, IFNα-PC showed positive correlations to serum creatinine, blood urea nitrogen, serum β2-microglobulin (s-β2MG), urinary total protein (U-TP), and urinary β2MG, in addition to the number of infiltrated macrophages per area of interstitium. In LP patients, negative correlations were shown between IFNα-PC and s-β2MG, U-TP, and U-N-acetyl-β-D-glucosaminidase. Conclusion: A significant positive relationship exists between IFNα-PC and the clinicopathological parameters of deteriorated renal lesions in the AP but not in the LP. Thus, the immune status influencing the functional damage may differ between these two phase.