Patients with severe lupus nephritis who have both diffuse proliferative (class IV) and membranous (class V) lesions on biopsy can be refractory to current monotherapy treatments. Bao et al.

The VSMC can undergo a proliferative response that underlies ... muscle cell in the natural history of the atherosclerotic lesion seems to be to act as a nidus for development of the lesions ...

That's the class V lesion. But there was acute and active proliferative lesion seen in about 50 to 60% of glomeruli, so somewhat exceeding the 50% cutoff, and this is how the pathologist arrived ...

The second lesion is proliferative bronchiolitis with intraluminal polyps, which is a steroid-reversible lesion developing from the internal layer that fills the lumen causing bronchiolitis ...