Rapid diagnosis of cytomegalovirus encephalitis in patients with AIDS using in situ hybridisation

Automated in situ hybridization and immunohistochemistry for cytomegalovirus detection in paraffin-embedded tissue sections

Cytomegalovirus (CMV) infections cause serious morbidity and mortality in immunocompromised individuals. CMV detection methods include serology, viral culture, polymerase chain reaction, and histologic examination [hematoxylin and eosin, immunohistochemistry (IHC), in situ hybridization (ISH)]. Until recently, ISH was performed manually. We compared automated ISH and automated IHC (Bond-max system, Leica Microsystems) in 72 cases (multiple organ systems) previously evaluated for CMV by conventional methods [hematoxylin and eosin, IHC (Dako Autostainer Plus), polymerase chain reaction, and/or viral culture]. By automated ISH, 27 cases were CMV-positive (25 positive, 2 equivocal on original diagnosis), 43 were negative (10 positive, 29 negative, 4 equivocal on original diagnosis), and 2 were equivocal (positive on original diagnosis). By automated IHC, 31 cases were CMV-positive (28 positive, 3 equivocal on original diagnosis), 39 were negative (7 positive, 29 negative, 3 equivocal on original diagnosis), and 2 were equivocal (positive on original diagnosis). Using original CMV diagnosis as gold standard, automated ISH and automated IHC had sensitivities of 67.6% and 75.7%, respectively (P value=0.25), and both had specificities of 100%. Combined automated ISH and IHC had sensitivity of 75.7% and specificity of 100%. Positive predictive values for automated ISH, automated IHC, and combination of ISH and IHC were 92.6%, 90.3%, and 90.3%, respectively. Negative predictive values were 67.4%, 74.4%, and 76.3%, respectively. We recommend either automated ISH or IHC for CMV detection in formalin-fixed, paraffin-embedded tissues. Although with moderate sensitivities, these methods have high specificities and positive predictive values, permit rapid turnover, require only set-up time, and result in strong stain intensity with minimal background.

In situ hybridization in cutaneous deep fungal infections: a valuable diagnostic adjunct to fungal morphology and tissue cultures

Dimorphic fungal infections (histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis) can occur in immunocompromised and healthy individuals. Cutaneous involvement is often secondary and may be the presenting sign of systemic disease. These ominous infections are frequently clinically indistinct, and patient prognosis is influenced by a timely diagnosis and treatment. Morphologic differentiation between these organisms is not definitive, and tissue cultures represent the diagnostic gold standard in current day practice. However, tissue cultures are rarely obtained and merely represent an afterthought in seemingly unsuspecting cases. Furthermore, when performed, they may take several days or weeks for completion. In situ hybridization (ISH) utilizing oligonucleotide probes directed against fungal ribosomal RNA is a rapid and accurate assay for the identification of dimorphic fungi in paraffin-embedded tissue sections. We present five patients in whom ISH both prospectively and retrospectively confirmed the presence of a cutaneous infection (histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis). In all of the skin sections analyzed, dimorphic fungi were morphologically apparent but not diagnostically discernible. In summary, ISH is a valuable tool in the prompt diagnosis of cutaneous deep fungal infections.

Rapid in situ hybridization technique for the detection of ribonucleic acids in tissues using radiolabelled and fluorescein-labelled riboprobes

In situ hybridization (ISH) is a useful diagnostic and research tool, but is also time consuming. This study was conducted to determine if a rate enhancement hybridization (REH) buffer, developed for membrane hybridization, could be used to decrease hybridization time for ISH. Tissue from swine with an enteric disease produced by a swine coronavirus, transmissible gastroenteritis virus (TGEV), was used as a model to standardize hybridization conditions for a rapid ISH technique. Small intestinal sections from pigs experimentally and naturally infected with TGEV were hybridized for various times at 52 degrees C and 70 degrees C with a radiolabelled or a fluorescein-labelled RNA probe in a standard hybridization or a REH buffer. Viral RNA was detected in intestines from as early as 30 min of hybridization by using both buffers with the radiolabelled probe; however, the signal was stronger with the REH buffer. With the fluorescein-labelled probe, viral RNA was detected in virus-infected cells of the intestines after 30 min of hybridization by using the REH buffer. Signal intensity was greater with the REH buffer than with the standard hybridization buffer when compared at each hybridization time and hybridization temperature using both radiolabelled and fluorescein-labelled probes. With the REH buffer, hybridization signal intensity was greater at 70 degrees C than at 52 degrees C for both probes. The best results were obtained when small intestinal sections were hybridized at 70 degrees C for 2 h using a radiolabelled or a fluorescein-labelled probe diluted in the REH buffer. The fluorescein-labelled RNA probe with REH buffer resulted in a minimal non-specific signal when compared with the radiolabelled probe. These studies demonstrated that the REH buffer can be used to decrease the time of ISH for the detection of viral RNA. This rapid ISH technique should have broad applications in the utilization of probe technology in diagnostics and research for the detection of target ribonucleic acids in situ

In situ hybridization and its diagnostic applications in pathology

In situ hybridization (ISH) is a technique by which specific nucleotide sequences are identified in cells or tissue sections. These may be endogenous, bacterial or viral, DNA or RNA. On the basis of research applications, the technique is now being translated into diagnostic practice, mainly in the areas of gene expression, infection and interphase cytogenetics. Diagnostic applications are most often based on short nucleotide sequences (oligomers) labelled with non-isotopic reporter molecules, and sites of binding may be localized by histochemical or immunohistochemical methods. The technique can be applied to routinely fixed and processed tissues; with some targets, it is even possible to obtain hybridization in autopsy material. ISH has been used to detect messenger RNA (mRNA) as a marker of gene expression, where levels of protein storage are low; for example, to confirm an endocrine tumour as the source of excess hormone production. Its application in infectious diseases has to date been mainly in viral infections, such as the typing of human papillomavirus (HPV) or the detection of Epstein-Barr virus by the presence of small nuclear RNAs (EBERs). The expression of mRNAs for histone proteins has been used to detect cells in S phase, and related methods may be applied to detect apoptotic cells. Using probes to chromosome-specific sequences, it is possible to detect aneuploidy, and to document changes in specific chromosomes, which may have prognostic significance in some tumours, such as B-cell chronic lymphatic leukaemia. Using sequence-specific probes, translocations can be identified, such as the t(11;12) of Ewing's sarcoma. This review presents an outline of the technique of in situ hybridization and discusses areas of current and potential diagnostic application.

Chemiluminescent in situ hybridization for the detection of cytomegalovirus DNA

A chemiluminescent in situ hybridization assay that could combine the sensitivity of chemiluminescent substrates, the specificity of digoxigenin-labeled probes, and the spatial morphological resolution and localization of the signal of the in situ hybridization was developed for the detection of cytomegalovirus (CMV) DNA. CMV DNA in cultured CMV-infected cells and in different clinical samples (tissue sections and cellular smears) was detected using digoxigenin-labeled probes constructed in our laboratory that were immunoenzymatically visualized employing anti-digoxigenin Fab fragments labeled with alkaline phosphatase and the chemiluminescent adamantil-1,2-dioxetane phenyl phosphate substrate for alkaline phosphatase. The luminescent signal from the hybrid formation was detected, analyzed, and measured with a high performance, low light level imaging luminograph apparatus connected to an optical microscope and to a personal computer for quantitative image analysis. Increasing values of emitted photons per second per infected cell, corresponding to the presence of hybridized CMV DNA, could be found in infected cells fixed at various times after infection, following the CMV replication cycle. When the assay was performed on different clinical samples from patients with acute CMV infections, CMV DNA was detected in all positive samples tested, both in cellular samples and in frozen and paraffin-embedded tissue sections, proving specific and sensitive. The chemiluminescent in situ hybridization assay developed in this work can be a useful tool for a sensitive and specific diagnosis of viral infection and can be easily adapted to detect and study any specific gene sequence inside the cells. The assay may also be promising for an estimation and quantification of nucleic acids present in tissue samples or cellular smears and for imaging gene expression in cells.