Distribution of ionized calcium-binding adaptor molecule 1-positive macrophages and papillary muscle fibrosis in dogs with myxomatous mitral valve disease.

INTRODUCTION/

OBJECTIVES

The aim of the study was to characterize the activated macrophage (ionized calcium-binding adaptor molecule-1-positive [Iba1+]) population in myxomatous mitral valve disease (MMVD)-affected valve leaflets and associated papillary muscle (PM), as well as fibrosis within the PM associated with MMVD.

ANIMALS, MATERIALS AND

METHODS

Mitral valve leaflets and posteromedial PM were collected from a total of 25 dogs consisting of three groups: normal group (normal valves; n = 6), mild group (mildly affected valves; n = 5), and severe group (severely affected valves; n = 14). Histological sections of mitral valves were assessed by immunohistochemistry for ionized calcium-binding adaptor molecule-1, and PM sections were similarly assessed for ionized calcium-binding adaptor molecule-1 and with Sirius red for fibrosis.

RESULTS

Significant increases in Iba1+ macrophages were noted in mitral valve leaflets from the severe group compared with the mild group (P=0.020) and the normal group (P=0.001). No significant difference in Iba1+ macrophages within the PM was noted between groups (P=0.662). Significant increases in the area of fibrosis were seen within the PM in the severe group compared with the normal and mild groups (P=0.001 and P=0.023, respectively).

STUDY LIMITATIONS: The sample size is small, and the dogs in the normal and MMVD-affected groups are not age-matched. Furthermore, many dogs from the tissue donation program lack complete health status information.

CONCLUSIONS

Inflammation may play an important role in canine MMVD. Further investigation is needed to determine if myxomatous changes in the valves or increased fibrosis in the associated PM are initiated by inflammation.