Cytokeratins in primary cutaneous amyloidosis

The expression of keratins was investigated immunohistochemically on formalin-fixed and snap-frozen primary cutaneous amyloidosis tissue with a panel of monospecific and polyspecific antikeratin antibodies, with recognized keratins K1, K5, K6, K7, K8, K10, K14, K16, K17, K18 and K19. Amyloid deposits in frozen sections of seven cases of macular amyloidosis and lichen amyloidosus always reacted with antibodies LP34 (labelling K5, K6 and K18), MNF 116 (labelling K5, K6, K8, K10, K17 and K18), and RCK 102 (labelling K5 and K8); frozen sections in one case each of the seven cases also reacted with antibodies LL001 (labelling K14), LP1K (labelling K7 and K17), and LP2K (labelling K19). In formalin-fixed sections of 13 cases of macular amyloidosis and lichen amyloidosus, amyloid deposits were labelled with LP34 in three sections, MNF 116 in four sections, LL020 (labelling keratins K5 and K6) in one section, and LP2K in two sections. In nodular primary cutaneous amyloidosis, amyloid deposits were not labelled with any antikeratin antibodies. These data confirm that amyloid in macular amyloidosis and lichen amyloidosus contains keratin epitopes, and suggests derivation of the fibrillar component from keratin intermediate filaments. Several different keratins appear to undergo conversion to amyloid. LP34, MNF 116 and RCK 102 antibodies, which have in common the labelling of keratin K5, may be useful in the diagnosis of macular and papular amyloidosis with frozen tissue sections.