Characterizing Ruminal T Cells in Lactating Dairy Cows.

Abstract

γδ T cells regulate immune responses via Interleukin-10 secretion and reduces cytotoxic and helper T cell proliferation, in vitro. γδ T cells are prominent in ruminant peripheral blood but their presence in rumen tissue remains unclear. Our study aimed to determine the relative proportions of T-cell types within rumen tissue, hypothesizing that the largest proportion would be γδ T-cells. Using an observational study, 3 ruminally cannulated Holstein dairy cows were monitored for 21 days. Dry matter intake and milk yield were measured daily. Milk samples, body condition scores, and bodyweight were assessed on d 2 and 9. Rumen pH was measured every 4 h for 24 h on d 2 and 11. Partial rumen evacuations on d 8 and 15 facilitated rumen tissue samplings for flow cytometric analysis. Blood samples for peripheral immune cell analysis were collected on d 8 and 15 immediately after rumen evacuations. Spectral flow cytometry assessed T cell proportions in blood and rumen tissue using a panel including CD45+ (leukocytes), CD3+ (T lymphocytes), CD4+ (Helper T cells), and TCRN-24+ (γδ T cell). Flow cytometry data were analyzed in JMP with a linear mixed model blood vs. rumen tissue. The cows remained clinically healthy, with dry matter intake at 26.0 ± 3.44 kg/d, and milk at 50.6 ± 12.99 kg/d (Mean ± SD). Rumen pH was within a normal range (6.06 ± 0.55). CD3+ cells constituted 95.6% ± 8.3% (Mean ± SEM) of all ruminal CD45+ cells compared to 63.6% ± 8.3% in blood. On aCD3+ basis, TCRN24+ cells were the most prominent subset of T lymphocytes in rumen tissue and were enriched compared to blood (87.9% ± 2.4% v. 6.5 ± 2.4%). The CD4+ were not enriched in the rumen compared to blood (0.7% ± 1.1% vs. 14.7 ± 1.1%). We observed a TCRN24+CD4+ population in the rumen which was largely absent in blood (6.6% ± 1.3% vs. 0.4 ± 1.3%). Understanding the role of T lymphocytes in rumen immunity may guide strategies to strengthen health and digestion while reducing inflammation in ruminants.No embargoAcademic Major: Animal Science