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Despite a lot of research efforts, the origin of renal fibroblasts is still matter of debate. Epithelial-mesenchymal transition (EMT) of tubular epithelial cells could be at least one of the mechanisms by which renal fibroblasts are generated. Every kind of renal injury is potentially able to induce renal tubular cells to go through the various steps of EMT and generate fibroblasts, as it has been demonstrated by experimental models, in vitro experiments, and renal biopsy studies. It means that, if EMT is a common process of progression of renal failure, further studies and a better understanding of this process can lead us to envisage specific treatments to counteract the progression of renal disease.

As reported in the previous chapter (Part I) the term amyloidosis refers to the deposition of an amorphous substance defined by the presence of fibrillary structure by electron microscopy and a characteristic betapleated sheet structure by X-ray diffraction. Renal biopsy is fundamental in diagnostic terms because morphological demonstration is necessary and the tissue most frequently involved by amyloidosis is the kidney. In the previous chapter we presented the different histochemical and immunohistochemical techniques that are necessary to differentiate the two main types of amyloidosis defined as AL and AA. Here we show the variability of deposition of amyloid in glomerular, vascular and interstitial compartments.

Renal involvement in type 2 diabetes is a well known clinical occurrence. According to data from the literature, besides diabetic glomerulosclerosis, type 2 diabetic nephropathy may occur as a non specific chronic damage mostly related to vascular changes, or as a glomerular disease superimposed on or even unrelated to diabetic glomerulosclerosis. The most common picture remains in any case diabetic glomerulosclerosis (diabetic GS), that is characterized by variable degrees of mesangial sclerosis.

Henoch-Schonlein purpura is a clinical syndrome characterized by the association of skin, joint, and gastrointestinal symptoms. Henoch-Schonlein purpura is characterized by wide-spread vasculitis. Although the clinical symptoms of this disease are characteristic, the diagnosis is not always easy to establish because other forms of systemic vasculitis - mainly the microscopic form of periarteritis nodosa - may mimic the disease. In addition, in contrast to systemic lupus erythematosus, there are no biological tests that can identify Henoch-Schonlein purpura with certainty. Immunofluorescence microscopic techniques have made an important contribution to both the diagnosis and the study of the pathogenesis of the disease, particularly since they have demonstrated the presence of IgA deposits in the glomeruli and in the vessel walls. These findings not only confirmed the immunologic nature of the pathologic lesions but also drew attention to the remarkable similarity between Henoch-Schonlein purpura nephritis and IgA nephropathy.

Membranous glomerulonephritis (MGN) is characterized by thickening of the glomerular basement membrane due to the presence of subepithelial immune deposits. From a morphological point of view, idiopathic MGN is indistinguishable from class V lupus nephritis. The glomerular lesion is extremely variable and the basement membrane thickening changes over time. According to the classic descriptions, MGN is in fact divided into four stages.

The characteristic and diagnostic lesion of idiopathic IgA nephropathy (IgAN, Berger's disease) is glomerular IgA deposition, as a unique or predominant positive immunoglobulin. Despite the relatively uniform feature of the immunohistological pattern, the morphological lesions observed by light microscopy are extremely variable. This variability in glomerular and interstitial alterations has frequently created some difficulties in histological classification.