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A simple and versatile technique for the preparation of ultra-thin sections, which can be stained immunohistochemically directly on electron microscope grids, is presented. An anti-hapten immunoperoxidase procedure has been adapted for use on tissue fixed in a purified monomeric glutaraldehyde--picric acid mixture, and embedded in 'L R White', a recently formulated plastic resin. This plastic tolerates the use of partial dehydration of tissue, resulting in higher antigenic yields. In addition, no etching of ultra-thin sections is necessary, and the whole immunostaining procedure can be completed in less than 2 h. A comparison of commonly used fixatives is discussed. High-resolution micrographs showing general staining (uranyl acetate--lead citrate) of rat pancreas, and immunostaining of insulin and TSH in storage granules in perfusion-fixed rat tissue and of lambda-chain immunoreactive cells in immersion-fixed human tonsil are included as examples.

ABSTRACT. This study examined the morphologic features of the parietal peritoneal membranes of 130 patients undergoing peritoneal dialysis (PD) and compared them with the features of the peritoneal membranes of normal individuals, uremic predialysis patients, and patients undergoing hemodialysis. The median thickness of the submesothelial compact collagenous zone was 50 μm for normal subjects, 140 μm for uremic patients, 150 μm for patients undergoing hemodialysis, and 270 μm for patients undergoing PD (P < 0.001 for all versus normal subjects). Compact zone thickness increased significantly with the duration of PD therapy [0 to 24 mo, 180 μm (n = 58); 25 to 48 mo, 240 μm (n = 24); 49 to 72 mo, 300 μm (n = 13); 73 to 96 mo, 750 μm (n = 16); >97 mo, 700 μm (n = 19)]. Vascular changes included progressive subendothelial hyalinization, with luminal narrowing or obliteration. These changes were absent in samples from normal subjects but were present in 28% of samples from uremic patients and 56% of biopsies from patients undergoing PD. In the PD group, the prevalence of vasculopathy increased significantly with therapy duration (P = 0.0001). The density of blood vessels per unit length of peritoneum was significantly higher for patients with membrane failure and was correlated with the degree of fibrosis (P = 0.01). For the first time, a comprehensive cross-sectional analysis of the morphologic changes in the peritoneal membranes of patients undergoing PD is provided. The infrequency of fibrosis in the absence of vasculopathy suggests that vasculopathy may predispose patients to the development of fibrosis. This study provides a sufficiently large cohort of samples to allow structure-function relationships to be established, as well as providing a repository of tissue for further studies.

Caveolae are flask-shaped invaginations of the plasmalemma which pinch off to form discrete vesicles within the cell cytoplasm. Biochemically, caveolae may be distinguished by the presence of a protein, caveolin, that is the principal component of filaments constituting their striated cytoplasmic coat. Squamous alveolar epithelial type I (ATI) cells, comprising approximately 95% of the surface area of lung alveolar epithelium, possess numerous plasmalemmal invaginations and cytoplasmic vesicles ultrastructurally indicative of caveolae. However, an ultrastructural appearance does not universally imply the biochemical presence of caveolin. This immunocytochemical study has utilised a novel application of confocal laser scanning and electron microscopy unequivocally to localise caveolin-1 to ATI cells. Further, cytoplasmic vesicles and flask-shaped membrane invaginations in the ATI cell were morphologically identified whose membranes were decorated with anti-caveolin-1 immunogold label. Coexistent with this, however, in both ATI and capillary endothelial cells could be seen membrane invaginations morphologically characteristic of caveolae, but which lacked associated caveolin immunogold label. This could reflect a true biochemical heterogeneity in populations of morphologically similar plasmalemmal invaginations or an antigen threshold requirement for labelling. The cuboidal alveolar epithelial type II cell (ATII) also displayed specific label for caveolin-1 but with no ultrastructural evidence for the formation of caveolae. The biochemical association of caveolin with ATI cell vesicles has broad implications for the assignment and further study of ATI cell function.

We describe two methods for rapid processing of biological tissues into LR White acrylic plastic. Both methods make use of LR White's compatibility with small amounts of water, enabling non-osmicated tissue to be only partially dehydrated before infiltration with the plastic, a procedure that improves the sensitivity of post-embedding immunocytochemistry. In addition, both methods are designed to reduce the time for which tissue is exposed to the damaging influence of the plastic monomer, which can cause extraction and sudden shrinkage. The tissue example used in the first method is immersion-fixed, surgically removed human pituitary which, by virtue of its thorough fixation, can be processed quickly at 50 degrees C using catalytic polymerization at room temperature. The concentration of the catalyst is critically set to prevent the temperature rising above 60 degrees C in the tissue blocks. Penetration of immunoperoxidase reagents into 330-nm LR White sections is demonstrated and possible modes of action are discussed. When "lightly" fixed tissue is processed as above, serious polymerization artifacts can result from autocatalysis. A second method, based on the first but employing slower polymerization at 0 degrees C, has therefore been developed. The high level of fine structure that can be retained using this method is illustrated by the demonstration of the trans-tubular Golgi in perfusion-fixed kidney of rat. Biotinylated lectin is localized to cells of the kidney proximal tubule with streptavidin-colloidal gold, to illustrate tissue reactivity. In a second example, the structure of the bacterial cell envelope is shown to be similar in appearance after partial dehydration and LR White embedding to that seen after progressive lowering of temperature, dehydration, and Lowicryl embedding.

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The distribution and severity of the neuropathological changes in 57 cases of Alzheimer's disease, and 11 patients with Down's syndrome were investigated with reference to the cerebellum. A modified silver stain and a monoclonal antibody raised against amyloid beta-protein were used to identify amyloid plaques. The highest incidence of amyloid plaques in the cerebellum (93%) was found in the group of patients who developed dementia before 65 years of age. This figure dropped to 56% in those patients with dementia beginning after 75 years. In 37 of these cases the distribution of the pathological changes of the disease were also examined in the brain stem. The severity of the pathological changes in the cerebellum corresponded to the involvement of the brain stem nuclei with connections to the cerebellar cortex. The possibility that the disease process spreads to the cerebellum by involving the fibres from the brain stem is discussed with reference to previous anatomical and neurochemical studies.