Immune response in dogs with myxomatous mitral valve disease: insights into monocyte and lymphocyte subtypes and natural killer cells

BACKGROUND: The immune response in dogs with myxomatous mitral valve disease (MMVD) is understudied. HYPOTHESIS/OBJECTIVES: Investigate the populations of monocyte subtypes, natural killer cells (NK cells), and T lymphocyte subtypes in dogs with MMVD and their relationships with selected cytokines and echocardiographic parameters at different stages of the disease and in comparison to healthy dogs. ANIMALS: Eighty-one client-owned dogs: 64 with MMVD (preclinical stage, compensated congestive heart failure [CHF], decompensated CHF) and 17 healthy dogs. METHODS: Cross-sectional study. Natural killer (NK) cells, monocyte subtypes, T lymphocyte subtypes, and B lymphocytes were identified using flow cytometry. Generalized linear models were used to compare variables between groups. Pairwise comparisons were performed using estimated marginal means with Tukey correction. P-value < .05 was considered significant. RESULTS: The percentage of monocytes was higher in dogs with compensated and decompensated CHF compared with preclinical dogs. The percentage of activated T helper lymphocytes was lower in compensated CHF compared with all other groups. No differences in percentages were found for monocyte subtypes, NK cells, cytotoxic, regulatory and double positive T lymphocytes, or B lymphocytes. Concentration of monocyte chemoattractant protein-1 was higher in the decompensated CHF compared with all other groups, and the concentration of keratinocyte chemotactic-like chemokine was higher in the decompensated CHF compared with the preclinical group. CONCLUSIONS AND CLINICAL IMPORTANCE: Higher concentrations and percentages of total monocytes and concentrations of proinflammatory cytokines in CHF suggest an inflammatory pathway in MMVD progression. Activated T helper lymphocytes may be downregulated in dogs with compensated CHF.