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Module IB Histochemistry Martin Špaček, MD (E-mail: [email protected]) http://www.lf3.cuni.cz/histologie What is histochemistry? • It is a histological technique used for studying chemistry of tissues and cells • • • • Histochemistry Enzyme histochemistry Immunocytochemistry In situ hybridization Histochemistry Examples of Histochemical Methods: Ions • Iron (ferric ions – Fe3+) • Perls’s reaction: – sections of tissues are incubated in a mixture of potassium ferrocyanide and hydrochloric acid – result: insoluble dark blue precipitate of ferric ferrocyanide • Diagnostic application: – patients with diseases that store iron (eg. hemochromatosis) Spleen – Perls (16) Histochemistry Examples of Histochemical Methods: Lipids • stained with dyes soluble in the lipids • eg. Sudan IV, Sudan black, Oil red, Nile blue • fresh frozen (cryostat) sections are used for the most authentic picture of tissue lipids Histochemistry Examples of Histochemical Methods: Nucleic Acids – DNA • Feulgen’s reaction: – hydrolysis of DNA by hydrochloric acid – this process leads to the formation of aldehyde groups – free aldehyde groups react with the Schiff reagent – result: insoluble red substance Histochemistry Examples of Histochemical Methods: Nucleic Acids – RNA • RNA-rich organelles are stained with basic dyes • i.e.: toluidine blue, methylene blue • Since the RNA is not the only basophilic substance in the tissue it is necessary to incubate a control slide with ribonuclease Kidney – methylene blue (20) Histochemistry Examples of Histochemical Methods: Saccharides • Saccharides can be detect by PAS reaction (periodic acid-Schiff) • it is based on oxidative action of periodic acid (HIO4) → aldehyde groups • these aldehyde groups react with Schiff’s reagent (as in Feulgen’s reaction) • → a new compound with a purple colour (PAS-positive substances) Histochemistry Examples of Histochemical Methods: Saccharides • PAS-positive substances are: – polysaccharides (glycogen) – glycosaminoglycans /mucopolysaccharides/ (hyaluronic acid, chondroitin sulphate) – proteoglycans – glycoproteins (thyreoglobulin, collagen) – glycolipids (lipofuscin) • Clinical application: – biopsies of tissues from patients with diseases that store glycogen (glycogenosis), glycosaminoglycans (mucopolysaccharidosis)... Spleen – PAS (17) Colon – PAS (19) Colon – PAS (19) Enzyme Histochemistry • Enzymes are the catalysts of most of biochemical reactions • Frozen tissues are used • Principle: – 1st reaction (histochemical): • enzyme + substrate → product – 2nd reaction: • demonstration of the product Enzyme Histochemistry – Examples • Peroxidase – sections are incubated in a solution containing hydrogen peroxide and DAB (diaminoazobenzidine) – DAB is oxidized in the presence of peroxidase – result: insoluble, black, electrondense precipitate • Clinical application: – diagnosis of leukemias (detection of the peroxidase activity in blood cells) • Peroxidase is used also as a label in immunocytochemistry and in ISH Enzyme histochemistry – Alkaline phosphatase in the proximal tubules of the kidney Enzyme histochemistry – Demonstration of aminopeptidase M in the proximal tubules of the kidney Immunocytochemistry • Is a technique for identifying cellular or tissue constituents (antigens) by means of antigen-antibody interactions • Antigens: – proteins, glycoproteins, proteoglycans • Antibodies: – serum proteins known as immunoglobulins – formed in the humoral immune system by plasma cells – there are five types of antibody found in the blood IgA, IgD, IgE, IgG and IgM. – IgG is the commonest and the most frequently used antibody for immunohistochemistry Antibodies An antibody molecule is composed of four polypeptide chains, two identical light chains and two identical heavy chains Antigenic Determinants (Epitopes) • The specific site of an antigen that binds to an antibody is called an antigenic determinant or epitope • Most antigens have a variety of epitopes that generate a number of different antibodies that are called polyclonal • A single immune response to an antigen is termed monoclonal Monoclonal antibodies • Monoclonal antibodies are “cloned” antibodies that all respond to exactly the same epitope of the same antigen – they are exceptionally specific • Activated B cells (plasma cells) contain a mixture of antibodies directed against different epitopes • Activated B cells have a limited lifetime when grown in culture • How can we select a single B cell clone (monoclonal) and propagate the cell line? Monoclonal antibodies • Antibodies can be raised in mice by injection of an antigen. • Repeated injections create a pool of activated B cells. Monoclonal antibodies • B lymphocytes can mutate into tumor cells that result in a type of cancer termed myeloma. • Myeloma cells become “immortal” and will grow indefinitely in culture. • Fusion of a single activated B cell and a myeloma cell will create a hybridoma that can grow indefinitely in culture Methods of Labelling Antibodies • • • • Enzyme labels (peroxidase) Colloidal metal labels (EM) Fluorescent labels Avidin-biotin techniques Fluorescent Compounds • Fluochromes are substances which can absorb radiation in the form of ultraviolet or visible light • This absorbed radiation causes an “excited state” followed by emission of radiation of a different wavelength • The fluorescent substances then appear as shiny particles on a dark background • Fluorochromes: FITC (fluorescein isothiocyanate), rhodamine, DAPI, etc. Fluorescent labels • The chromatine is stained with a blue fluorescent probe – DAPI Fluorescent labels – FITC • Appearance Na+/K+ ATPase in basolateral labyrint of proximal and distal tubule of kidney Avidin-biotin Techniques • These methods rely on the affinity of the glycoprotein avidin for biotin • Biotin, a low molecular weight vitamin, is easily conjugated to antibodies and enzyme markers • Up to 150 biotin molecules can be attached to one antibody molecule → increased sensitivity Skin / keratine – ABC (22) Skin / Melanocytes and Langerhans cells Anti - S - 100 antibody, eccrine sweat glands of the skin Pancreas / insulin – ABC (21) Pancreas / somatostatin in the D cells of the islets of Langerhans Antibody labels neurofilaments of neurons in the cortex of brain Antibody labels neurofilaments in Purkinje cells and in axons of basketlike cells Cerebrum / astrocytes – ABC (96) Methods of Localizing Antigens • Direct method – primary antibody is conjugated directly to the label • Indirect method (more sensitive) – first step: nonlabeled anti-x antibody is bound to the antigen – second: the labeled antiantibody binds to the anti-x antibody In Situ Hybridization Techniques • Allow the demonstration of specific nucleic acid sequences in their cellular environment • Are based on hybridization of a nucleic acid probe (small lengths of nucleic acid of known base sequence) to the target • Applications: – detection of abnormal genes – identification of viral infection, etc. In Situ Hybridization Techniques • Probes labelling: – radioisotopes – coupling of the nucleotides with biotin – fluorescent labels (FISH) Fluorescence in Situ Hybridization (FISH) Fluorescence in Situ Hybridization (FISH) Immunohistochemistry + ISH Human Papillomavirus DNA demonstrated by In Situ Hybridisation (pink) in epithelial cells identified by indirect immunofluorescence using antibody against cytokeratin (green)