Enzyme histochemistry and immunohistochemistry with freeze-dried or freeze-substituted resin-embedded tissue

Delineation of the healthy rabbit lung by immunohistochemistry - a technical note

Investigation and studies of pulmonary diseases and injuries require pre-clinical animal models. The rabbit lung model is widely used and allows for a diverse set of readouts. Among them, histology and immunohistochemistry are of invaluable merit because qualitative and quantitative information about tissue morphology and composition can be easily obtained. In this technical note, we performed several histological and immunohistochemical stainings in the rabbit healthy naïve lung tissue. Overnight formalin fixation with subsequent paraffin embedding was compared to cryopreservation with a subsequent 10-minute formalin fixation prior to staining. Antigen retrieval (AR) for paraffin embedded sections proved to enhance the corresponding signals compared to analogous staining without AR. Advantages and disadvantages of chromogenic versus immunofluorescence stainings were discussed. In addition, several morphological structures, such as the intrapulmonary bronchus with its mucosal folds, the pulmonary artery, the alveoli and the lymph nodes, were stained with various stainings at the same site in order to give a comprehensive picture of their composition. Besides Haematoxylin&Eosin and Elastica van Gieson staining, collagen I, collagen III, fibronectin, α-SMA, ki-67 and protease-activated receptor-2 (PAR-2) immunohistochemistry was performed. Collagen I, collagen III and fibronectin expression was positive at the outer rim of the pulmonary arteries, while the inner rim was collagen III positive. Moreover, the fibronectin staining in the intrapulmonary bronchus showed an opposite trend when compared to the collagen III staining. The alveoli exhibited PAR-2 expression, while PAR-2 was not expressed in lymph nodes of the healthy rabbit lung.

Freeze-substitution: origins and applications

Freeze-substitution is a physicochemical process in which biological specimens are immobilized and stabilized for microscopy. Water frozen within cells is replaced by organic solvents at subzero temperatures. Freeze-substitution is widely used for ultrastructural and immunocytochemical analyses of cells by transmission and scanning electron microscopy. Less well recognized is its superiority over conventional chemical fixation in preserving labile and rare tissue antigens for immunocytochemistry by light microscopy. In the postgenome era, the focus of molecular genetics will shift from analyzing DNA sequence structure to elucidating the function of gene networks, the intercellular effects of polygenetic diseases, and the conformational rearrangements of proteins in situ. Novel strategies will be needed to integrate knowledge of chemical structures of normal and abnormal macromolecules with the physiology and developmental biology of cells and tissues from whole organisms. This review summarizes the progress and future prospects of freeze-substitution for such explorations.

Co-localization of multiple antigens and specific DNA. A novel method using methyl methacrylate-embedded semithin serial sections and catalyzed reporter deposition

Co-localization of proteins and nucleic acid sequences by in situ hybridization and immunohistochemistry is frequently difficult as the process necessary to detect the target structure of one technique may negatively affect the target of the other. Morphological impairment may also limit the application of the two techniques on sensitive tissue. To overcome these problems we developed a method to perform in situ hybridization and immunohistochemistry on semithin sections of methyl methacrylate-embedded tissue. Microwave-stimulated antigen retrieval, signal amplification by catalyzed reporter deposition, and fluorescent dyes were used for both techniques, yielding high sensitivity and excellent morphological preservation compared to conventional paraffin sections. Co-localization of in situ hybridization and immunohistochemistry signals with high morphological resolution was achieved on single sections as well as on adjacent multiple serial sections, using computerized image processing. The latter allowed for the co-localization of multiple antigens and a specific DNA sequence at the same tissue level. The method was successfully applied to radiation bone marrow chimeric rats created by transplanting wild-type Lewis rat bone marrow into TK-tsa transgenic Lewis rats, in an attempt to trace and characterize TK-tsa transgenic cells. It also proved useful in the co-localization of multiple antigens in peripheral nerve biopsies.

Histological and histochemical changes in the digestive tract of white sturgeon larvae during ontogeny

Ontogenetic changes in digestive tract histology and digestive enzyme histochemistry were investigated 11 to 36 days post-hatch in white sturgeon Acipenser transmontanus larvae. From initiation of exogenous feeding (12 days post-hatch), larvae were fed a commercial salmonid diet for the ensuing 24 days. The digestive system of white sturgeon displayed a high degree of morphologic organization and functionality at the onset of exogenous feeding. An enhancement of digestive capacities occurred with transition to active feeding. On day 2 of feeding, there was a clear increase of alkaline phosphatase, aminopeptidase M, dipeptidyl peptidase IV, and γ-glutamyl transpeptidase activity in the brush border of the spiral intestine. This strong activity is an apparent confirmation of the importance of this segment of the intestine for protein digestion and nutrient absorption. The functional development of the pyloric intestine occurred on day 4 and was concomitant with an increase in the activity of brush border and cytoplasmic enzymes such as acetylcholinesterase, dipeptidyl peptidase II, α- and β-galactosidases. The absence of acetylcholinesterase, lactase, nonspecific esterase, and weak activity of exopeptidases and alkaline phosphatase in the anterior intestine suggests that this segment of the intestine may be less important in nutrient absorption than the pyloric and spiral intestines. The observed quantitative and qualitative differences in enzyme activity along the intestine indicate a high degree of specialization of each segment for specific digestive and absorptive processes.

Resin embedding for quantitative immunoelectron microscopy. A comparative computerized image analysis

Quantitative immunoelectron microscopy (QIEM) is dependent on the reliability of preparative techniques for both efficient immunolabeling and consistent quantitative results among series of immunostained sections. The present study compared Lowicryl K4M and Epon embedding after identical fixation and dehydration of rat somatotrophic secretory granules. Labeling intensity, diameter, roundness, uptake of uranyl acetate, and gray value were measured with computer assisted image analysis. Lowicryl-embedded granules showed the highest labeling densities after conventional fixation and Progressively Lowering Temperature (PLT) dehydration, but values were not consistent in a series of immunostained sections. A lower but more uniform level of immunostaining was seen in Epon-embedded sections when tissue was cryofixed and physically dehydrated. Gray value measurements from micrographs from both embedding media confirmed the better contrast of Epon sections and the different reliefs of the granule surfaces. This study emphasizes the importance of complete comparisons of preparative techniques for QIEM for reliability and reproducibility.

Quantitative aspects of enzyme histochemistry on sections of freeze-substituted glycol methacrylate-embedded rat liver

Freeze-substituted rat liver embedded in glycol methacrylate (GMA) has been used to demonstrate the activities of several enzymes. The following enzymes could be detected in GMA-sections by the indicated histochemical procedure(s): 5'-nucleotidase (lead salt, cerium-diaminobenzidine), alkaline phosphatase (indoxyl-tetrazolium salt), catalase (diaminobenzidine), acid phosphatase (diazonium salt), lactate dehydrogenase (tetrazolium salt) and glutamate dehydrogenase (tetrazolium salt). The activities of all these enzymes were dramatically decreased compared with the activities demonstrated in unfixed cryostat sections, with the exception of catalase. The activities of the following enzymes could not be detected in GMA-sections: glucose-6-phosphate dehydrogenase (tetrazolium salt), xanthine oxidoreductase (tetrazolium salt), D-amino acid oxidase (cerium-diaminobenzidine-cobalt-hydrogen peroxide) and glucose-6-phosphatase (cerium-diaminobenzidine). The possible role of restricted penetration of reagents into the resin was studied by measuring cytophotometrically the enzyme activities in GMA-sections of 3 and 6 microns in thickness. For all the enzymes that could be detected, the 6 microns:3 microns ratio varied from 1.4 to 2.7. An eventual retarded penetration of reagents into the resin was investigated by measuring cytophotometrically the amount of final reaction product during incubation for acid phosphatase and glutamate dehydrogenase activities. In both cases linear relationships without a lag phase were found for the specific enzyme activities with incubation time. Chemical denaturation of proteins or masking of active sites in proteins due to embedding in the resin monomer may be considered to be the main cause of decreased enzyme activities.