Peripheral blood lymphocyte subtypes in dogs with different stages of myxomatous mitral valve disease

Background Data on alterations in peripheral blood lymphocyte (PBL) subtypes in dogs with myxomatous mitral valve disease (MMVD) is lacking. Objectives To investigate PBL subtypes and their correlation with parameters of inflammation and MMVD progression markers in dogs with different stages of MMVD. Animals Seventy‐eight client‐owned dogs: 65 with MMVD (American College of Veterinary Internal Medicine [ACVIM] classification stages B2, C, and D) and 13 healthy controls. Methods Prospective cross‐sectional study. Complete cardiac assessment, flow cytometry (T lymphocytes [CD3+], their subtypes [CD3+CD4+, CD3+CD8+, CD3+CD4+CD8+, CD3+CD4−CD8−], and B lymphocytes [CD45+CD21+]) and measurement of N‐terminal pro B‐type natriuretic peptide, cardiac troponin I, and C‐reactive protein concentrations were performed. Results The percentage of CD3+CD4+ lymphocytes was significantly lower in stable ACVIM C patients ( P  = .01) and unstable ACVIM C and D patients ( P  = .003), the percentage of CD3+CD8+ lymphocytes was significantly higher in stable ACVIM C patients ( P  = .01) and unstable ACVIM C and D patients ( P  = .01), CD3+CD8+ lymphocyte concentration was significantly higher in unstable ACVIM C and D patients ( P  = .05), and the CD3+CD4+/CD3+CD8+ ratio was significantly lower in stable ACVIM C patients ( P  = .01) and unstable ACVIM C and D patients ( P  = .01) compared with healthy controls. Conclusions and Clinical Importance The percentages of CD3+CD4+ and CD3+CD8+ PBL and CD4+/CD8+ ratio were altered in MMVD dogs with congestive heart failure (ACVIM C, D), but not in ACVIM B2, suggesting involvement of these PBL subtypes in the pathogenesis of congestive heart failure in dogs with MMVD.