Neutrophils, monocytes and other immune components in the equine endometrium: Friends or foes?

The article studies the role of various immune components such as neutrophils and monocytes in the equine endometrium (uterus lining), and their impact on reproductive functioning and uterine disorders. It also discusses the influence of hormones like estrogen on immune responses and the possible role of certain immune cells in complications like endometritis and fibrosis.

Role of Immune Mechanisms in Equine Reproduction

• The article initially focuses on establishing the importance of innate and adaptive immune mechanisms in regulating the reproductive functions and health of the equine uterus. The paper especially shines a light on the role of an innate immune response influenced by estrogen, playing a predominant role during the follicular phase.
• The authors suggest that an increase in immune-related genes during estrus might play a role in uterine clearance post mating. They also emphasize that immune cells and their products like cytokines are critical in the development and maintenance of the luteal phase, regression of the corpus luteum, and in early stages of pregnancy.

First Line of Defence: Innate Immune Response

• The paper further discusses the role of the innate immune response as a nonspecific, first line of defense against pathogens and foreign stimuli. This includes the constituents of seminal fluid and local infections like endometritis.
• Recent findings suggest that neutrophil extracellular traps (NETs), which restrain bacteria through a mechanism not reliant on phagocytosis, play a role in the pathogenesis of equine endometrial fibrosis (endometrosis).

Pro-fibrotic Role of Persistent Immune Cells

• The article also sheds light on the potential pro-fibrotic roles of persistent macrophages and mast cell activation. These cells could exacerbate fibrosis in the endometrium by secreting large amounts of pro-fibrotic factors.
• The review aims at highlighting the crucial roles of key immune system components and their products in both healthy and aberrant equine uterine function.