Decoy cells

Decoy Cells are virally infected epithelial cells that can appear in a urine sample, which although appearing malignant are actually shed cells infected with the BK virus.

People who have had a kidney transplant are likely to have decoy cells. When the body rejects, and or the kidneys aren’t functioning properly it increases the amount of toxins and pollutants in the body that regularly wouldn’t be there and can create immune deficiencies. This then (re) activates the BK virus and it starts attacking the nuclei of the cells lining the uroepithelium and the renal tubules. (kidney tubules). This causes the nuclei to swell to a much larger size and thus the creation of decoy cells.^[1] This could lead to the failing of the kidneys or help with the alteration of the way the normal bodily functions are carried out with the kidneys and ultimately lead to further complications resulting in kidney failure which could possibly lead to another transplant or death.^[2]

The most frequent disorder caused by PVBK is a nephropathy characterized by tubular changes often associated with interstitial inflammation and tubulitis, the distinguishing lesion being tubular cells whose nuclei are heavily altered by viral inclusion bodies.

Some studies have been done with testing the actual amount of decoy cells in the urine that correlate with what exactly is happening with the kidneys. It is believed that contrary to having more decoy cells in the urine say that you are more likely to develop kidney failure. Many tests have been done but there is insufficient truth to this theory that is referenced.^[3] In the experience of some authors, the higher the number of ‘decoy cells’ in the urine, the greater the probability of finding the PVBK nephropathy . In contrast, other investigators have reported that even when the ‘decoy cells’ are ‘abundant’, the positive predictive value is as low as 27%, which indicates that ‘decoy cells’ may be present without any clinical disease. Patients at higher risk of developing PVBK nephropathy are those who have ‘decoy cells’ in the urine in association with impaired renal function and repeated episodes of acute rejection, and are under treatment with tacrolimus and/or mycophenolate mofetil.^[4]

Decoy cells can be seen with Papanicolaou staining or phase-contrast microscopy. The cells appear with the enlarged nuclei and can appear in clumps like cancer would which hence gives them the name “decoy cells” which give them the appearance of a malignant cancerous cell and for the fact that they can be found all over in the kidney tubules and uroepthelium. A malignant cancer cell will try to escape the region it is in, find its way into the bloodstream and infect other regions of the body. The decoy cells give off some of the very same features.^[5]

By Papanicolaou stain, most ‘decoy cells’ show a much enlarged nucleus, which is occupied by a basophilic inclusion surrounded by chromatin that confers a ground-glass or gelatinous appearance. Sometimes the nuclear inclusion has a vesicular aspect, or it may be surrounded by a halo, and the chromatin may be clumped . When ‘decoy cells’ derive from the uroepithelium, the heavily enlarged and altered nuclei as well as the irregular shape of the cell body can mimic the changes observed in neoplastic cells.

By phase-contrast microscopy, ‘decoy cells’ show the same abnormalities described for stained specimens, namely, enlargement of the nucleus with a ground-glass or vesicular appearance, altered chromatin, enlarged nucleoli, the presence of a halo, and at times also cytoplasmic vacuoles . In our experience, these features make ‘decoy cells’ different from tubular cells and transitional cells found in all other conditions. The only exception is represented by cells infected by cytomegalovirus, which frequently show a ‘bird's eye’ appearance.^[6][7]

There has also been testing done to calculate the amount of decoy cells within the urine as well after taking samples of urine and testing it.^[8] Childhood infection with polyomaviruses leads to a life-long latent infection of renal and urinary tract epithelia. Replication in the reno-urinary epithelium is associated with viral cytopathic changes such as nuclear inclusions and decoy cells. During the 2005-2009 period, cytological urine analysis was performed in 154 samples (94 male and 60 female) from patients with kidney transplantation (n = 19), simultaneous pancreas-kidney transplantation (SPKT) (n = 9) and simultaneous kidney and liver transplantation (n = 2). Urine samples were analyzed monthly following transplantation according to the protocol. The period from transplantation to the first occurrence of decoy cells in the urine and the period of decoy cell persistence in the urine were assessed. The presence of decoy cells (< 10 and > 10 decoy cells) and red blood cells (< 20 E, 20-100 E and > 100 E) per cytospin smear was semiquantitatively determined, along with analysis of inflammatory cells (neutrophilic granulocytes) and fungi. In patients with decoy cells detected, their sensitivity, specificity, and negative and positive predictive value for BK virus nephropathy were calculated. Correlation of the study parameters was estimated by use of Kruskal-Wallis test (STATISTICA 7.1, StatSoft Inc., Tulsa, USA). Decoy cells were found in 30 patients (20 male and 10 female), age median 40 (range 16-69) years, at a mean of day 115 (range day 5-747) post transplantation, whereas their presence was recorded for a mean of 141 (range 77-771) days. Immunohistochemical staining of kidney biopsy sample for polyomavirus (SV40 large T-antigen) yielded positive reaction in 2/30 (7%) patients. Erythrocyturia was present in 29/30 patients with decoy cells. The number of decoy cells per cytospin smear generally ranged less than 10 in 25/30 patients, whereas more than 10 decoy cells per cytospin smear were only recorded in 5/30 patients. Immunohistochemistry produced positive finding for BK virus in one patient with SPKT and simultaneous kidney and liver transplantation each, which was statistically significantly more common as compared with patients with kidney transplantation alone (p = 0.0244). Immunohistochemical positivity for BK virus was more significant in cases with more than 10 decoy cells detected in cytospin smear (p = 0.013). In BK nephropathy, the finding of urinary decoy cells showed a 100% sensitivity, 84% specificity, 100% negative predictive value and 6% positive predictive value. BK virus nephropathy remains a significant post transplantation complication.

References

1. ^ http://ndt.oxfordjournals.org/cgi/content/full/19/4/1015-a
2. ^ http://www.landesbioscience.com/curie/chapter/2224/
3. ^ http://ndt.oxfordjournals.org/cgi/content/full/16/7/1496#R1
4. ^ http://ndt.oxfordjournals.org/cgi/content/full/16/7/1496#R1
5. ^ http://ndt.oxfordjournals.org/cgi/content/full/16/7/1496#R1
6. ^ http://www.ncbi.nlm.nih.gov/books/NBK6541/figure/A40311/?report=objectonly
7. ^ http://www.landesbioscience.com/curie/images/chapters/Nickeleit1color.jpg
8. ^ . PMID 20432744.