In a previous paper from this laboratory, the production of monoclonal antibodies recognizing antigenic determinants common to the alpha and beta chains of bovine brain S-100 protein was reported. In the present study, the immunohistochemical labeling patterns of these monoclonal antibodies against a wide range of normal and pathologic human tissues are described, and these results are compared with those obtained using polyclonal anti-S-100 antiserum. Although many of the reactions of the monoclonal antibodies were very similar to those of the polyclonal antiserum (and the previously reported sites of S-100 immunoreactivity) several additional cell types (e.g., thyroid follicular cells, biliary epithelium, pancreatic cells, renal tubules) were labeled by one or both of the monoclonal antibodies. Blocking experiments prove that immunohistochemical differences obtained with monoclonal and polyclonal antibodies are at least partly caused by differences in the repertoire of antigenic determinants on S-100 protein that are recognized by the two species (i.e., mouse and rabbit, respectively). These results indicate that S-100 may be more widespread in human tissues than previously thought, and that its value as a marker of the histogenetic origin of human tumors should be reappraised. It is suggested that the marked variability observed in the reactivity of different tissues in the present study may indicate that S-100 is a heterogeneous group of molecules, and its expression may be related to the functional activity of cells.

A new type of ground-glass hepatocyte is described. The appearance is due to pale, homogeneous, weakly eosinophilic inclusions filling a portion of or the entire hepatocytic cytoplasm. On haematoyxlin and eosin stained sections, these cells closely resemble ground-glass hepatocytes described in other conditions. However, they are negative on special stains for HBsAg and on PAS staining. Immunohistochemically, they reveal a selective and exclusive positivity for fibrinogen. On electron microscopy, the immunoreactive fibrinogen appears as amorphous, fluffy or granular material within dilated cisternae of the rough endoplasmic reticulum. This finding suggests intracellular storage possibly reflecting a defective intracellular transport of fibrinogen.

A histological study was performed on liver biopsies from patients with acute hepatitis A (n = 13), B (n = 35) and non-A, non-B (nAnB) (n = 35) in search for microscopical features characteristic for each type of hepatitis. Biopsies from two centres (Padova, Italy and Leuven, Belgium) were studied in order to determine whether the histological pattern in acute hepatitis A, B and nAnB may differ from one centre to another. The histology of cases of hepatitis A and B from Italy and Belgium did not differ. Less liver cell plemorphism was found in hepatitis A than in B. Clear differences were observed between acute hepatitis nAnB occurring in Padova when compared with cases from Leuven. The Padova-biopsies obtained from patients with transfusion-induced viral hepatitis were mainly characterized by a high degree of lympho-histiocytic intrasinusoidal infiltration whereas the Leuven-biopsies, mostly taken in patients with sporadic hepatitis, were characterized by the presence of numerous acidophilic bodies and Mallory body-like cytoplasmic alterations. Morphologically, the latter cases appear to be closely related to hepatitis B.

Biopsies of normal skin and benign and malignant skin tumours were studied immunohistologically with nine monoclonal antibodies. The study showed that monoclonal antibodies can clearly delineate antigens expressed in different regions of normal skin and that, in general, tumours retain the antigenic pattern characteristic of the region from which they have arisen. These findings indicate the potential value of analysing these patterns of antigenic expression with a panel of monoclonal antibodies both for understanding the pathogenesis of skin tumours (e.g. basal cell carcinomas) and in their differential diagnosis (e.g. squamous cell carcinoma versus keratoacanthoma).

ABSTRACT— The predictive value of piecemeal necrosis (PMN) in acute hepatitis was investigated in 62 patients (39 hepatitis B virus infection, 9 hepatitis A virus infection and 14 possible hepatitis NANB virus infection). The 62 initial biopsies were blindly recoded and classified into three groups: 1. Acute hepatitis with signs of possible transition to chronicity (AHTC) (n = 35)(i.e. a picture of acute hepatitis associated with PMN). 2. AHTC‐borderline group (BL) (n = 15) (i.e. a picture of acute hepatitis with minimal PMN). 3. Uncomplicated acute hepatitis (AH) (n = 12) (i.e. a picture of acute hepatitis without PMN). Follow‐up of the patients revealed an evolution to chronicity in a very high percentage of the AHTC‐cases of hepatitis B (95%) and NANB (89%) etiology. Also 67% of the BL‐cases of hepatitis B etiology developed chronic liver disease. In hepatitis B the immunohistochemical pattern of HBsAg is of additional help. In hepatitis A, PMN is often present (5/9) but no evolution to chronicity was observed. This study shows that PMN in acute hepatitis appears to be a useful prognostic feature for chronicity in hepatitis B and NANB.