Effects of susceptibility of mares to endometritis and stage of cycle on phagocytic activity of uterine-derived neutrophils.

The study investigates how susceptibility to endometritis in mares and their stage of cycle affects the ability of neutrophils derived from the uterus to engulf microbes, a process known as phagocytic activity. The findings reveal that the susceptibility to endometritis doesn’t affect the phagocytic function of neutrophils, and that neutrophils from resistant mares were more active during oestrus than dioestrus.

Study Participants and Procedure

• The study used fourteen mares divided into two groups: a group of seven mares who were susceptible to bacterial endometritis and another group of seven mares who were resistant to it.
• Neutrophils from both the circulating blood and the uterus of these mares were studied.
• The uterine neutrophils were obtained by inoculating cell-free filtrates of Streptococcus zooepidemicus, a bacterium associated with equine bacterial endometritis.
• The mares were scheduled for collection of neutrophils at two different stages of their reproductive cycle: oestrus and dioestrus.

Chemiluminescence Assay

• The phagocytic activity of the neutrophils was assessed using a chemiluminescence assay, a method often used to measure production of reactive oxygen species, which is a key process in phagocytosis.
• This involved addition of the bacteria Streptococcus, which had been treated to promote engulfment by phagocytic cells (opsonized).

Key Findings

• The chemiluminescence generated by neutrophils in the blood was found to be higher (statistically significant at P<0.05) in mares susceptible to endometritis than in those that were resistant.
• The stage of cycle had no effect on the chemiluminescence generated by circulating neutrophils.
• Neutrophils derived from the uterus of susceptible mares generated more chemiluminescence (indicating more phagocytic activity) than those from resistant mares, but this was less statistically significant (P<0.1).
• There was an interaction between susceptibility to endometritis and stage of cycle with respect to uterine neutrophil activity: neutrophils from resistant mares produced more chemiluminescence in oestrus than in dioestrus. However, this was not observed in susceptible mares.

Conclusions

• The susceptibility of mares to endometritis was not related to any defects in phagocytic function of the neutrophils in the uterus.
• Phagocytic activity of neutrophils from resistant mares was greater during oestrus than during dioestrus.