Leukocyte populations in peripheral blood of dromedary camels with clinical endometritis

Abstract

Endometritis represents the main cause of reproductive failure in dromedary camels. In dromedary camels, associations between endometritis-causing pathogen-species, disease severity, and systemic changes in the immune system have not been evaluated. In the current study, there was use of flow cytometry and immunofluorescence of membrane proteins for the evaluation of leukocyte subsets and the cellular phenotype in blood of camels with clinical endometritis and evaluations of associations with disease severity and endometritis-causing pathogens. Animals with endometritis had markedly larger numbers of total leukocytes and neutrophils. Although total lymphocyte and monocyte counts did not differ between camels with and without clinical endometritis, there were lesser numbers of total and effector CD4-positive T cells in camels with endometritis. Among monocytes, number of camel inflammatory monocytes (Mo-II) was markedly greater, whereas Mo-III numbers were less in the blood of camels with clinical endometritis. Number of inflammatory monocytes was also indicative of endometritis severity grade. Among camels with clinical endometritis, E. coli- and S. aureus-infected animals had similar endometritis grades and comparable phenotype and composition patterns of leukocytes. Neutrophils and monocytes of camels with clinical endometritis had fewer cell adhesion molecules (i.e., CD11a and CD18). Collectively, the results from the current study allowed for identification of associations between endometritis severity grade and larger numbers of inflammatory monocytes. The results also indicate there is no association between endometritis pathogen-species and changes in phenotype or composition of blood leukocytes.

Introduction

Uterine infections, mainly caused by bacterial and fungal pathogens, are considered to be the primary cause of reproductive failure in dromedary camels (Wernerry and Kumar, 1994; Ali et al., 2010a; Shawaf et al., 2019). In camels, endometritis is associated with large economic losses as a result of increased calving intervals and culling of useful breeding animals (Bellows et al., 2002). When there are female dromedary camels with infertility problems, clinical endometritis is the most common clinical finding (Ali et al., 2018).

For camels, Escherichia coli, Staphylococcus aureus, Streptococcus sp., Trueperella pyogenes and Proteus sp. represent the most common bacterial species isolated from the uterus of females with clinical endometritis (Ali et al., 1987; Tibary et al., 2006; Refaat et al., 2020).

When there is an endometritis condition, pathogen sensing by the uterine innate immune system induces a local inflammatory response with increased production of cytokines, which are responsible for the recruitment of immune cells and the induction of adaptive immunity (Herath et al., 2009; Sheldon et al., 2009). Adhesion molecules, such as CD11a and CD18, are cell surface molecules with essential functions in leukocyte adhesion to blood endothelial cells and migration into inflamed tissues (Nourshargh and Alon, 2014).

Peripheral blood monocytes of dromedary camels have been recently classified into three different subsets with phenotypic and functional differences (Hussen et al., 2020). In the major subset of camel monocytes there is a large abundance of surface CD14, however, a small abundance of surface MHCII (Mo-I, CD14^highMHCII^low). Camel inflammatory monocytes have a large abundance of both markers (Mo-II, CD14^highMHCII^high), while the third monocyte subset has a small abundance of CD14 with a large abundance of MHCII (Mo-III, CD14^lowMHCII^high) (Hussen et al., 2020).

To the best of our knowledge, there have been no studies conducted of the effects of endometritis on leukocyte immunophenotype of dromedary camels. The aim of the current study, therefore, was to characterize endometritis-associated changes in the composition and phenotype of peripheral blood leukocytes and determine how this is affected by endometritis-causing pathogen or disease severity.