Quantitative and functional dynamics of circulating and endometrial polymorphonuclear leukocytes in healthy peripartum dairy cows

The aim of the present study was to assess the counts, viability, and functionality of circulating and endometrial polymorphonuclear leukocytes (PMN) isolated from fourteen clinically and metabolically healthy multiparous dairy cows in the peripartum period. For this, blood samples were collected at -5, +9, +21 and + 37 days (d) relative to calving. Cytology samples were collected from the vagina, cervix, and uterus at +9, +21 and + 37 d, using the cytobrush technique. Additional vaginal samples were collected at -5 d. Cytology smears were prepared and the PMN-to-all nucleated cell proportions (PMN%) were calculated. The endometrial cytobrush samples were also used for flow cytometric assessment of endometrial PMN (ePMN) viability and functionality. Functionality tests for circulating PMN (cPMN) included phagocytosis (PC), oxidative burst, and intracellular proteolytic degradation. For ePMN, we evaluated PC only. The effect of day relative to calving on PMN viability and functionality were fitted in linear regression models, accounting for repeated measures. The endometrial PMN% were higher at +9 d (23.5 +/- 0.4%; least-squares means +/- standard error) and +21 d (8.5 +/- 0.3%) than at +37 d (1.4 +/- 0.3%). No changes in PMN% were found on either vaginal or cervical cytology along the peripartum period. The cPMN counts were higher pre- (6.2 +/- 0.4 x 10(6)/mL) than postpartum (4.9 +/- 0.4 x 10(6)/mL). Upon viability analysis, only the percentage of viable cPMN tended to be lower at -5 d (90.1 +/- 1.5%) than at +37 d (94.1 +/- 1.4%), and no other changes in the percentage of apoptotic and necrotic cPMN, nor in their functionality were found during the peripartum period. Analysis of ePMN viability showed that the percentage of viable ePMN did not change over time. In marked contrast, the percentage of apoptotic ePMN was higher at +9 d (37.8 +/- 5.1%) than at +21 d (20.9 +/- 5.1%) and +37 d (11.9 +/- 5.3%), while the percentage of necrotic ePMN was lower at +9 d (27.0 +/- 6.3%) than at +37 d (54.9 +/- 6.6%). The percentage of ePMN PC was higher at +9 d (27.5 +/- 3.4%) than at +37 d (13.3 +/- 4.9%). In conclusion, during the peripartum period ePMN in the healthy postpartum uterus are highly dynamic in terms of counts, viability, and functionality compared to their circulating counterparts. (C) 2021 Published by Elsevier Inc.