Determination of urinary and serum myeloperoxidase and interleukin-6, -8 -10 in dogs with subclinical bacteriuria and urinary tract infections

Subclinical bacteriuria (SBU) is defined as the presence of significant bacteriuria in dogs, in the absence of clinical signs attributable to lower urinary tract infection (UTI). The local immunological factors potentially associated with the asymptomatic phenotype displayed in dogs with SBU, have not been explored. This study aimed to investigate the local immune response in dogs with SBU through cytokine and myeloperoxidase (MPO) expression in urine. Furthermore, we aimed to investigate the discriminatory potential of urinary interleukin 6 (uIL-6), uIL-8, uIL-10 and uMPO between dogs with SBU and UTIs (cystitis and pyelonephritis). ILs and MPO were analyzed with canine and human commercially available sandwich enzyme-linked immunosorbent assays (ELISA), respectively. In total 54 dogs were included in the study counting 14, 15, seven and 18 SBU, cystitis, pyelonephritis and non-bacteriuric control dogs, respectively. The study found higher uIL-8 levels in dogs with bacteriuria and levels increasing with disease severity. UIL-8 levels also differed between dogs with SBU and pyelonephritis, although overlapping values hindered reliable classification of individual dogs as having either SBU or UTI. UMPO concentrations increased with disease severity and differed between dogs with pyelonephritis and SBU without overlapping values. Notably, no differences in uMPO were detected between non-bacteriuric control dogs and dogs with SBU indicating a reduced neutrophil activity in dogs with SBU compared to dogs with UTI. These results suggest a discriminatory potential of MPO in canine SBU and UTIs, making it an interesting candidate for further investigation. UIL-6 and uIL-10 were undetectable in most urine samples.