Clonality Test by PCR - PARR in Real Time of Canine Lymphomas
Background: Lymphoma is a neoplasm of hematopoietic origin that affects canines. The proper establishment of prognosis and rapid institution of treatment are essential for a better quality of life, and immunophenotyping is one of the tools used for this purpose. The objective of this study was to perform a clonality test for immunophenotypic characterization of canine lymphomas using the polymerase chain reaction (PCR) for antigen receptor rearrangements (PARR) technique in real-time from samples fixed in formalin and embedded in paraffin.
Materials, Methods & Results: The 23 analyzed samples were fixed in formalin and embedded in paraffin canine lymphoma from the Collection Laboratory of Histopathology of the Animal Pathology Area of the Departament of Veterinary Medicine - Federal Rural University of Pernambuco UFRPE. Samples were processed, their DNA was extracted, quantified, diluted, and standardized at a concentration of 50 ng/µL. After extraction, all samples were subjected to conventional PCR for endogenous control (detection of the IgM target region), in which the extracted DNA was amplified in a final volume of 25 µL. The 128 bp amplified product was detected by 1.5% agarose gel electrophoresis. Of the 23 samples analyzed for the detection of the conserved region referring to the endogenous gene, 91.30% (21/23) amplified the conserved region Cµ by conventional PCR, and two samples 8.70% (2/23) were negative. Endogenous control positive samples were subjected to real-time PCR-PARR for detection of IgH Major (LB), IgH Minor (LB), and TCRγ (LT) target regions. All reactions were performed in duplicate to reduce the risk of false-positive or false-negative results due to technical errors. Samples previously confirmed by immunohistochemistry were used as positive controls for T cell and B cell lymphoma, and MilliQ water was used as a negative control. After amplification, the melting curve gradually increased the temperature by 1C/5 s to 95C during continuous fluorescence monitoring. Of the 21 samples analyzed, 100.00% (21/21) demonstrated clonal amplification. Of these, 57.15% (12/21) were positive for phenotype B, and 42.85% (9/21) were positive for phenotype T.
Discussion: Due to the importance of researching and confirming samples from files fixed and embedded in paraffin samples in laboratories, PCR-PARR is a good tool for this purpose. In the present study, real-time PCR analysis demonstrated greater sensitivity in the characterization of the immunophenotype of lymphomas from old samples fixed in formalin and embedded in paraffin. The temperature of melting curve analysismay vary depending on the amount of DNA and its quality. In the present study, it was found that the average melting temperature in the samples varied between ± 3C when compared to that in the control sample for LB and LT, 83.5C and 80C, respectively: in the literature, there is a relative difference in this temperature, which may vary up to 4C. Real-time PCR-PARR was satisfactory in the characterization of the immunophenotype of canine lymphomas from formalin-fixed and paraffin-embedded samples; therefore, its use is recommended for both retrospective studies. The use of PCR-PARR associated with histopathological and/or cytopathological examination in cases of canine lymphomas strongly helps pathologists, provide a safe establishment of the immunophenotype, minimize errors, and optimize the diagnosis, thus directly contributing to the establishment of the prognosis.
Keywords: immunophenotyping, lymphoproliferative disease, real-time PCR, TCRγ, IgH.
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