Table 1. Original World Health Organization (WHO) classification of lupus nephritis (1974)
| Class I | Normal glomeruli (by light microscopy, immunofluorescence, and electron microscopy) |
| Class II | Purely mesangial disease |
| a. Normocellular mesangium by light microscopy but mesangial deposits by immunofluorescence or electron microscopy | |
| b. Mesangial hypercellularity with mesangial deposits by immunofluorescence or electron microscopy | |
| Class III | Focal proliferative glomerulonephritis (<50%) |
| Class IV | Diffuse proliferative glomerulonephritis (≥50%) |
| Class V | Membranous glomerulonephritis |