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Vet Microbiol. 2014 Jun 4;170(3-4):197-205. doi: 10.1016/j.vetmic.2014.01.014. Epub 2014 Feb 3.

Diagnostic utility of CD4%:CD8 low% T-lymphocyte ratio to differentiate feline immunodeficiency virus (FIV)-infected from FIV-vaccinated cats.

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  • 1Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, 625 Harrison St., West Lafayette, IN 47907, USA. Electronic address:
  • 2Research and Development Department, IDEXX Laboratories, Westbrook, ME, USA.
  • 3Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, 625 Harrison St., West Lafayette, IN 47907, USA.
  • 4Department of Comparative Pathobiology, College of Veterinary Medicine, Purdue University, 785 Harrison Street, West Lafayette, IN 47907, USA.


Antibody testing based on individual risk assessments is recommended to determine feline immunodeficiency virus (FIV) status, but ELISA and Western blot tests cannot distinguish between anti-FIV antibodies produced in response to natural infection and those produced in response to FIV vaccination. The aim of this cross-sectional study was to test the hypothesis that FIV-infected cats could be differentiated from FIV-vaccinated uninfected cats using lymphocyte subset results, specifically the CD4%:CD8(low)% T-lymphocyte ratio. Comparisons of the CD4%:CD8(low)% T-lymphocyte ratio were made among the following four groups: Group 1 - FIV-infected cats (n=61; FIV-antibody positive by ELISA and FIV PCR positive); Group 2 - FIV-uninfected cats (n=96; FIV-antibody negative by ELISA); Group 3 - FIV-vaccinated uninfected cats (n=31; FIV-antibody negative by ELISA before being vaccinated against FIV, after which they tested FIV ELISA positive); and Group 4 - FIV-uninfected but under chronic/active antigenic stimulation (n=16; FIV-antibody negative by ELISA; all had active clinical signs of either upper respiratory tract disease or gingival disease for ≥ 21 days). The median CD4%:CD8(low)% T-lymphocyte ratio was lower in Group 1 (1.39) than in each of the other three groups (Group 2 - 9.77, Group 3 - 9.72, Group 4 - 5.64; P<0.05). The CD4%:CD8(low)% T-lymphocyte ratio was also the most effective discriminator between FIV-infected cats and the other three groups, and areas under ROC curves ranged from 0.91 (compared with Group 4) to 0.96 (compared with Group 3). CD4%:CD8(low)% shows promise as an effective test to differentiate between FIV-infected cats and FIV-vaccinated uninfected cats.


CD4; CD8(low); Cat; Diagnosis; FIV Vaccine; Retrovirus

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