Abstract
In humans and mice, the detailed phenotypic and functional characterization of peripheral blood monocytes allows for identification of three monocyte subsets. There are also evidences of monocyte phenotypic heterogeneity in other species, including cattle, sheep, pig and horse. However, little is known about such variability in dogs. The aim of the study was to determine whether and how peripheral blood monocytes of healthy dogs differ in the presence of MHCII and CD4 and in the basal production of reactive oxygen species (ROS). Three distinct subsets of CD11b+CD14+ monocytes were found in peripheral blood samples of healthy dogs, based on the variations in the density of MHCII and CD4 surface molecules: MHCII+CD4– (Mo1), MHCII+CD4+ (Mo2) and MHCII–CD4+ (Mo3). The Mo2 and Mo3 were significantly lower in percentage than Mo1 but their basal ROS production was higher. Within the Mo2 and Mo3 subsets, the percentage of cells producing ROS was significantly higher comparing to cells lacking this activity. Canine peripheral blood monocytes vary in the expression of MHCII and CD4 and in the activity suggesting that cells within the three identified subsets carry out different functions. The higher production of ROS in non-activated cells within small subsets of Mo2 and Mo3 monocytes might indicate their immunomodulatory potential.
Highlights
Phenotypic heterogeneity of monocytes in humans was firstly described in 1989 [1]
The aim of the study was to determine whether and how peripheral blood monocytes of healthy dogs differ in the presence of MHCII and CD4 and in the basal production of reactive oxygen species (ROS)
Gibbons et al hypothesized that CD14–MHCII+ monocytes were equivalent to human non-classical monocytes, while CD14+MHCII+ represented intermediate and CD14+MHCII−was classical monocytes in the dog
Summary
Phenotypic heterogeneity of monocytes in humans was firstly described in 1989 [1]. Currently, the classification of monocytes in human blood includes three subsets: classical CD14++CD16–, non-classical CD14+CD16++ and intermediate CD14+CD16+ [2]. Each subset is specialized in certain activity, including the production of cytokines, reactive oxygen species (ROS) and phagocytosis [3]. They seem to be differently involved in many types of human diseases, including coronary disease, asthma or tuberculosis [4, 5, 6]. CD16 (cluster of differentiation 16; Fcγ receptor III) is primarily known as a marker of natural killer cells It binds to antibodies and participates in signal transduction, which stimulates cytotoxic activity of natural killer cells and leads to the transcription of genes encoding cytokines and other factors [10, 11]. Similar role of CD16 on monocytes has been reported [12]
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