Mallory bodies: lesions of hepatocytes containing proteins of the keratin-myosin-epidermin group

A comparative study of myosins and prekeratin in epithelial cells of methacarn-fixed tissues

Around the turn of the century, tonofibrils and contractile myofibrils were observed within the same cells. These findings have been largely forgotten. To clarify the topical relations of these proteins in epithelial cells, duplicate sections of methacarn-fixed human and canine tissues were treated with the tannic acid-phosphomolybdic acid (TP)-Levanol Fast Cyanine 5RN reaction for myosins and the PAP technic for prekeratin, respectively. In bronchi, lingual and sweat glands, liver and pancreas, myosin was confined to the terminal bar-terminal web system, including pericanalicular layers. Prekeratin occurred throughout the epithelium of bronchi and ducts; secretory cells showed little or no reaction. Observations on myosin in kidney confirmed data by Harper et al. (1970). The PAP technic colored transitional epithelium and collecting tubules intensely; convoluted tubules did not react. Staining of segments of Henle's loops varied from case to case. Both reactions colored thymic epithelial cells. In myoid cells of Hassall's corpuscles myosin was gradually replaced by prekeratin and keratin. Basal cells of epididymis reacted strongly with the PAP technic, but did not contain myosin. Prekeratin is apparently identical with epidermin, whose composition and structure were well known in the 1950's. Epidermin undergoes chemical changes as cells move from the stratum basale to the stratum corneum. According to DAKO, the antibodies used in this study were prepared with prekeratin extracted from stratum corneum. Data in the literature and observations in this investigation indicate that some samples of antibodies do not react with all tonofilaments.(ABSTRACT TRUNCATED AT 250 WORDS)

On the chemistry of formaldehyde fixation and its effects on immunohistochemical reactions

Formalin has been recommended as an innocuous fixative for immunohistochemistry. However, several studies demonstrated impairment or blocking of antigenic activity of certain proteins. Formalin fixation was discovered accidentally by F. Blum in 1893 and its deleterious effects on various tissue structures were discussed extensively during the following decades. More recently, some authors assumed that formaldehyde bound to tissues can be largely or completely removed by washing and dehydration. According to chemical data, formaldehyde forms highly reactive methylols with uncharged amino groups. Such methylol groups yield methylene bridges with suitably spaced amides, arginine and aromatic amino acid sidechains. Only loosely bound formaldehyde is removed by washing for several hours. Residual bound formaldehyde cannot be dislodged by washing for weeks, but some formaldehyde is gradually removed when tissues are stored in water for an extended number of years. Methylene crosslinks resist treatment with high concentrations of urea, and can be broken only by drastic hydrolysis. It appears unlikely that such firmly bound formaldehyde is removed by conventional washing and dehydration procedures used in histochemistry. The superiority of methacarn, alcohol or acetone over formaldehyde fixation for immunohistochemical demonstration of prekeratin, myosin, type I and type IV collagen, laminin and fibronectin can be ascribed to the irreversible alterations of tissue proteins by formaldehyde.