Indian Journal of Pathology and Microbiology

: 2010  |  Volume : 53  |  Issue : 2  |  Page : 347--350

Decoy cells in the urine cytology of a renal transplant recipient: An immunohistochemical study

K Raveendran Pillai1, K Jayasree1, Ramdas Pisharody2, Elizabeth K Abraham1,  
1 Division of Pathology, Regional Cancer Centre, Thiruvananthapuram - 695011, Kerala, India
2 Department of Nephrology, Medical College, Thiruvananthapuram - 695011, Kerala, India

Correspondence Address:
K Raveendran Pillai
Division of Pathology, Regional Cancer Centre, Medical College P.O, Thiruvananathapuram - 695 011, Kerala


Human polyoma virus causes renal dysfunction and graft loss as a result of tubulo-interstial nephritis in renal transplant recipients after reactivation of latent virus in renal epithelium. The infected cells in the urinary sediments are characterized by large homogenous inclusions, which may cause diagnostic error in urine cytology. The epithelial cells with polyoma viral inclusions in urine cytology specimens are termed Decoy cells to caution pathologists not to misdiagnose these cells as cancer cells. We present a case of polyoma viral changes detected the first time in our laboratory in the urine of a 46year old male who underwent renal transplantation six months back and followed by immunotherapy. Urine cytological examination showed decoy cells and subsequently revealed on histopathology. Immunoperoxidase staining for SV-40 LT antigen (LT ag), expression of proliferating cell nuclear antigen (PCNA), p53 and Rb genes were also studied in the tissue sections for further observation. The expression of SV40 LT ag was negative, while PCNA showed strong positivity; p53 and Rb were expressed moderately in the nuclei of cells in the tubules. The report of a case of decoy cells in the urine of a patient with renal transplantation focuses the importance of cytologic analysis of urine as a diagnostic tool for screening renal transplant recipients at risk of polyoma viral infection.

How to cite this article:
Pillai K R, Jayasree K, Pisharody R, Abraham EK. Decoy cells in the urine cytology of a renal transplant recipient: An immunohistochemical study.Indian J Pathol Microbiol 2010;53:347-350

How to cite this URL:
Pillai K R, Jayasree K, Pisharody R, Abraham EK. Decoy cells in the urine cytology of a renal transplant recipient: An immunohistochemical study. Indian J Pathol Microbiol [serial online] 2010 [cited 2021 May 14 ];53:347-350
Available from:

Full Text


Human polyoma virus (PV) causes renal dysfunction and graft loss in renal transplant patients and has become more frequent in recent years as a result of the use of newer and more effective immunosuppressive drugs. [1] Sachdeva et al.[2] reported a high incidence of PV infection in Indian transplant recipients. In our knowledge, very few reports of PV infection in renal transplant recipients are available from South India. [3] PV infected cells are occasionally reported in urine cytology and there is limited information on their incidence in the histologic specimens. [4] The term "decoy cells"was coined for epithelial cells with polyoma viral inclusions in urine cytology specimens to avoid their misinterpretation as malignant cells. [5],[6] We present a case of polyoma viral changes in the epithelial cells of urine of a middle-aged male who underwent renal transplantation. As urine samples are routinely received in most cytology laboratories, awareness among cytotechnologists and cytopathologists about PV infection in the appropriate clinical context can help to identify decoy cells in the urine. In this report we provide details of the cytologic, histologic and immunohistochemical features of PV infection in the renal epithelium of a renal transplant patient.

 Case Report

A 46-year-old male, who underwent renal transplantation six months back and on immunotherapy, was admitted with septic shock due to urinary tract infection. There was history of recurrent urinary tract infection and microscopic hematuria after transplantation. On examination the renal function of the patient was worsening and showed signs of rejection. Microbiological and biochemical analyses were performed. Routine examination of the urine showed presence of many E. coli. Serum creatinine was elevated (4.1 mg/dl). Urine cytological examination showed decoy cells. At the same time, percutaneous gun biopsy was performed from the upper pole of the transplanted kidney and histopathological examination revealed PV infection. To make a definite diagnosis of PV infection, immunoperoxidase staining for SV40 LT ag and expression of proliferating cell nuclear antigen (PCNA), p53 and Rb genes were performed in the renal biopsy. However the patient died immediately after the diagnosis.

Exfoliative Cytology

Three consecutive days early morning urine samples were collected. Cytospin smears were prepared from the sediments and fixed immediately in 95% ethyl alcohol. All the smears were moderately cellular with occasional small clusters and dispersed large atypical cells. Cells were round or elongated with a high nuclear cytoplasmic ratio and moderate to abundant and basophilic cytoplasm along with many inflammatory cells [Figure 1]. Cells were usually mononucleated and occasional binucleated cells with smudgy chromatin. Cells with varied nuclear morphology were noted in the same smear [Figure 2] a-d. Some of the cells showed enlarged nuclei with coarse chromatin and irregular nuclear membrane [Figure 1]. Presence of large round homogenous viral inclusions appeared as smudgy dots in the nuclei [Figure 1]d. A few large binucleated cells characterized by homogenous, amorphous basophilic ground -glass like intranuclear inclusion bodies and a condensed rim of chromatin in the periphery of the nuclear membrane [Figure 2]a. Occasional cells had a very thin clear halo between the inclusion and a thick appearing nuclear membrane.


On gross examination, two gray white bits of renal biopsies and the larger measuring 0.6 x 0.1 cm size. Microscopically, two glomeruli were observed in the biopsy specimens. Capillary loops were dilated and congested. Tubular atrophy was visible [Figure 3]. Tubules were lined by cells with pleomorphic-smudged nuclei and nuclear inclusions of amorphous basophilic ground glass variants were noted in some of the cells [Figure 4]. Collections of lymphocytes were infiltrated in the inerstitium.


Histologic sections were prepared for immunohistochemical staining for SV40 LTag (Oncogene Research, San Diego, California, USA). The antibody reacts with BK, JC and SV40 polyoma virus LTag and is nonreactive with SV40 small T antigen. LT ag forms complexes with protein p53, which is required for initiation of viral DNA replication during lytic growth and also binds to Rb gene protein. Representative sections were also stained for PCNA and P53 (Dako, USA) and Rb (Santa Cruz Biotechnology, California, USA). Only nuclear staining was regarded as a positive reaction for SV40 LTag, PCNA, P53 and Rb immunohistochemical staining. The expression of SV40 LTag in the tissue section was negative. PCNA showed strong positivity [Figure 5] while P53 [Figure 6] and Rb [Figure 7] showed moderate nuclear staining in the tubules.


Polyoma virus causes allograft dysfunction in 2-5 % of renal transplant recipients in India. [2] Very few reports regarding PV infection are available from South India. [3],[7] As the number of renal transplant recipients is recently increasing in South Indian states, cytologic analysis of urine for detecting decoy cells is an important and cost effective tool for screening renal transplant patients at risk for PV nephropathy.

A morphologic sign of the (re)activation of PV is the detection of typical intranuclear viral inclusion bearing 'decoy cells' in the urine. [5],[8] The diagnostic gold standard for viral interstial nephritis is the morphological and immunohistochemical demonstration of polyoma viral infection and damage to tubular epithelial cells in renal biopsies. [4],[9] In this case we initially detected the decoy cells in the urine sediments and also revealed viral inclusions in the renal biopsy of the patient. The number of diagnostic cells in the urine specimens varies sparse to abundant, often with varied morphology. [8]

Most common are classic decoy cells characterized by large homogenous, amorphous basophilic ground -glass like intranuclear inclusion bodies and a condensed rim of chromatin. These features were clearly observed in this case and hence the diagnosis was easier.

PV-infected cells have more degenerative changes, and cells with large nuclei usually have proportionally abundant cytoplasm. Particular attention has to be paid for distinguishing decoy cells from malignant cells. The former have perfectly rounded nuclei and are found only as isolated cells in contrast to tumour cells, which may form groups and have irregular nuclei. [6],[8] The presence of detectable decoy cells in the urine correlates with the viral load of urine samples. PV inclusions in biopsy tissue are intracellular with a homogenous basophilic or amphophillic appearance. [8] In the histopathologic sections of this case, viral inclusions appeared to be smaller than their expected size due to shrinkage artifact during formalin fixation. Intense PCNA staining gave strong signals in decoy cells and inclusion bearing cells. This intense staining expression in this case should not be misinterpreted as a sign of marked cell proliferation, but rather indicate replication of viral DNA.

The immunohistochemical expression of LT ag in the kidney biopsy of this patient was negative. Since the LT ag is only expressed in abundance during the early phase of viral replication, decoy cells with late stages of polyoma assembly may be "T antigen" negative. [8] This immunostain was helpful for ruling out the presence of PV in 2% of biopsy specimens that showed markedly reactive tubular cells resembling PV infection. [8] Though the expression of LT ag was negative in this case, the coexpression of p53 and Rb showed moderate positivity and it could be due to the known interaction of LT ag with the p53 and Rb proteins. The virus utilizes the LT ag to induce cell division in the host cells and also LT ag inactivates the p53 protein and binds to Rb gene protein. [10] The abnormally accumulated p53 and Rb can be detected immunohistochemically.When p53 is inactivated by LT ag, there occurs progressive cellular hyperplasia and nuclear atypia, which will regress when p53 function is restored. [1],[10]

However these changes will progress to overtly malignant tumours, if p53 remains inactive for much longer period and will persist even when p53 activity is restored. Herawi et al. [2] found that even a combination stain for both p53 and LT ag may not reserve the nature of ambiguous cells, as some cells with reactive atypia may co-express both markers and some malignant cells may not show p53 overexpression in the presence of LT ag positive staining. Thus the interpretation of p53, Rb and LT ag staining as diagnostic tools to distinguish reactive from neoplastic urothelial atypia is difficult.

Drachenberg et al.[9] observed that urine samples seem to be the most sensitive and cost effective screening method for PV infection. They also found that immunohistochemical stains are useful to confirm the presence of PV, but do not increase the sensitivity of diagnosis, if this is not already suspected on routine light microscopy. Also PV changes may be focal and therefore not sampled in direct tissue biopsies. All these explanations focused the lack of a gold standard to confirm the diagnosis of PV infection. Decoy cells are more valuable than ever as a herald of a serious disorder in the transplanted kidney. [10] This simple test of urine sediment is now mandatory in all organ transplant recipients. [4],[5] Thus careful search of routine Papanicoloau stained urine specimens for decoy cells is a simple and important tool to identify patients at risk of developing PV nephropathy and, especially, to exclude the presence of the disease. In renal transplant patients the application of immunohistochemical analysis to search for PV genome should be made only after the detection of decoy cells in urine.


1Drachenberg C, Hirsch H, Ramos E, Papadimitriou J. Polyoma virus disease in renal transplantation: review of pathological findings and diagnostic methods. Hum Pathol 2005;36:1245-55.
2Sachdeva MS, Nada R, Jha V, Sakhuja V, Joshi K. The high incidence of BK polyomavirus infection among renal transplant recipients in India. Transplantation 2004;77:429-31.
3Radha S, Tameem A, Fernandez DK. Cytological diagnosis of infections in renal allograft recipients. Cytol 2007;24:130-3.
4Herawi M, Parwani AV, Chan T, Ali SZ Epstein JI. Polyoma virus-associated cellular changes in the urine and bladder biopsy samples: A cytohistologic correlation. Am J Surg Pathol 2006;30:345-50.
5Koss LG. On decoy cells. Acta Cytol 2005;49:233-4.
6DeMay RM. Urine: The art and science of cytopathology, Exfoliative Cytology. Chicago: American Society of Clinical Pathologists (ASCP);1996. p. 394-5.
7Shah KV, Goverdhan MK, Ozer HL. Neutralizing antibodies to SV40 in human sera from South India: search for additional hosts of SV4. Am J Epidemiol 1971;93:291-7.
8Singh HK, Bubendrof L, Mihatsch MJ, Drachenberg CB, Nickeleit V. Urine cytology findings of polyomavirus infections. In: Ashan N, editor. Polyomaviruses and Human Diseases. 1 st ed. Georgetown, T.X. : Springer Science +Business Media, Landes Bioscience/; 2006. p. 201-12.
9Drachenberg CB, Beskow CO, Cangro CB, Bourquin PM, Simsir A, Fink J, et al. Human polyoma virus in renal allograft biopsies: Morphological findings and correlation with urine cytology. Hum Pathol 1999;30:970-7.
10Boldorini R, Brustia M, Veggiani C, Barco D, Andorono S, Moga G, et al. Periodic assessment of urine and serum by cytology and molecular biology as a diagnostic tool for BK virus nephropathy in renal transplant patients. Acta Cytol 2005;49:235-43.