Figure 2.
Pathology of MGRS lesions with organized Ig deposits. (a-c): AL amyloidosis: review of Congo red stain under the Texas red immunofluorescence filter reveals bright red smudgy deposits in glomeruli, vessels, and focally in the interstitium (a,  × 100). The deposits on transmission EM are composed of randomly oriented straight fibrils (b,  × 40 000). On immunofluorescence, smudgy amyloid deposits in glomeruli and interstitium stain positive for lambda light chain (c,  × 200) but not for kappa light chain (not shown). (d-f): Immunotactoid glomerulopathy. The glomerulus exhibits global mesangial and endocapillary hypercellularity with intracapillary infiltrating lymphocytes and monocytes (d, PAS,  × 400). The deposits on EM are composed of microtubular structures with parallel alignment (e,  × 40 000). On immunofluorescence, there is bright granular to semilinear glomerular positivity for IgG (f,  × 400) and kappa light chain but not for lambda light chain (not shown). (g-i): Light chain proximal tubulopathy. Numerous osmophilic crystals with needle and rod shapes are seen within proximal tubular cells (g, toluidine blue–stained EM survey section,  × 400). EM reveals the engorgement of proximal tubular cells by rhomboidal and rod-shaped crystals, causing compression of the nuclear contours (h,  × 4400). Immunofluorescence on paraffin tissue after antigen retrieval with pronase reveals staining of proximal tubular cells for kappa light chain (i,  × 400) but not for lambda light chain (not shown). (j-l): Light chain CSH. There is interstitial infiltration of histiocytes containing intracytoplasmic red crystalline inclusions (j, trichrome stain,  × 400). A high-power EM image shows rhomboidal and rod-shaped intralysosomal crystals in an interstitial histiocyte (k,  × 8000). Immunofluorescence on paraffin tissue after antigen retrieval with pronase reveals staining of crystals within interstitial histiocytes for kappa light chain (l, ×400) but not for lambda light chain (not shown). (m-o): Light chain crystalline podocytopathy. Podocytes are filled with trichrome-red crystalline inclusions. There is partial collapse of the underlying glomerular tuft (m, trichrome stain,  × 600). High-power EM image shows highly electron dense crystals within podocytes (n,  × 8000). Many rod-shaped and rhomboidal inclusions within podocytes stain positive for kappa light chain by immunofluorescence on paraffin tissue after antigen retrieval with pronase (o,  × 400) but not for lambda light chain (not shown). (p-r): Crystalglobulin-induced nephropathy. Many eosinophilic, needle-shaped crystals are present within glomerular capillaries, associated with a macrophage-rich inflammatory reaction and mild mesangiolysis (p, hematoxylin and eosin,  × 600). Large highly electron-dense extracellular crystals are seen plugging the glomerular capillaries. Similar but fewer crystals are also seen in the subendothelial region and mesangium (q, EM,  × 8000). Large crystals in vessels stain brightly for IgG by immunofluorescence on paraffin tissue after antigen retrieval with pronase (r,  × 400) and kappa light chain but not for lambda light chain (not shown).

Pathology of MGRS lesions with organized Ig deposits. (a-c): AL amyloidosis: review of Congo red stain under the Texas red immunofluorescence filter reveals bright red smudgy deposits in glomeruli, vessels, and focally in the interstitium (a,  × 100). The deposits on transmission EM are composed of randomly oriented straight fibrils (b,  × 40 000). On immunofluorescence, smudgy amyloid deposits in glomeruli and interstitium stain positive for lambda light chain (c,  × 200) but not for kappa light chain (not shown). (d-f): Immunotactoid glomerulopathy. The glomerulus exhibits global mesangial and endocapillary hypercellularity with intracapillary infiltrating lymphocytes and monocytes (d, PAS,  × 400). The deposits on EM are composed of microtubular structures with parallel alignment (e,  × 40 000). On immunofluorescence, there is bright granular to semilinear glomerular positivity for IgG (f,  × 400) and kappa light chain but not for lambda light chain (not shown). (g-i): Light chain proximal tubulopathy. Numerous osmophilic crystals with needle and rod shapes are seen within proximal tubular cells (g, toluidine blue–stained EM survey section,  × 400). EM reveals the engorgement of proximal tubular cells by rhomboidal and rod-shaped crystals, causing compression of the nuclear contours (h,  × 4400). Immunofluorescence on paraffin tissue after antigen retrieval with pronase reveals staining of proximal tubular cells for kappa light chain (i,  × 400) but not for lambda light chain (not shown). (j-l): Light chain CSH. There is interstitial infiltration of histiocytes containing intracytoplasmic red crystalline inclusions (j, trichrome stain,  × 400). A high-power EM image shows rhomboidal and rod-shaped intralysosomal crystals in an interstitial histiocyte (k,  × 8000). Immunofluorescence on paraffin tissue after antigen retrieval with pronase reveals staining of crystals within interstitial histiocytes for kappa light chain (l, ×400) but not for lambda light chain (not shown). (m-o): Light chain crystalline podocytopathy. Podocytes are filled with trichrome-red crystalline inclusions. There is partial collapse of the underlying glomerular tuft (m, trichrome stain,  × 600). High-power EM image shows highly electron dense crystals within podocytes (n,  × 8000). Many rod-shaped and rhomboidal inclusions within podocytes stain positive for kappa light chain by immunofluorescence on paraffin tissue after antigen retrieval with pronase (o,  × 400) but not for lambda light chain (not shown). (p-r): Crystalglobulin-induced nephropathy. Many eosinophilic, needle-shaped crystals are present within glomerular capillaries, associated with a macrophage-rich inflammatory reaction and mild mesangiolysis (p, hematoxylin and eosin,  × 600). Large highly electron-dense extracellular crystals are seen plugging the glomerular capillaries. Similar but fewer crystals are also seen in the subendothelial region and mesangium (q, EM,  × 8000). Large crystals in vessels stain brightly for IgG by immunofluorescence on paraffin tissue after antigen retrieval with pronase (r,  × 400) and kappa light chain but not for lambda light chain (not shown).

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