Impact of Ambient Temperature on Bovine Viral Diarrhea Virus and Infectious Bovine Rhinotracheitis Vaccination Response

Abstract Vaccines are created to help the immune system fight pathogens faster and more effectively, but little is known on how season of the year impacts the immune system response to vaccination. This research was conducted to evaluate how ambient temperature (summer vs fall) impacted antibody production and immune cell type changes in Brahman and Brahman-influenced cows. Cows (n = 18) were immunized (2 mL I.M.) with a combination Modified Live Vaccine for Bovine Viral Diarrhea Virus (BVDV) and Infectious Bovine Rhinotracheitis Virus (IBR) on d 0 in either July 2022 (Summer; n = 12) or November 2022 (Fall; n = 6). Blood samples (30 mL/cow) were collected on d -3, 0, 2, 4, 6, 8, 10, 14 post vaccination and transferred to 50 mL conical tubes containing EDTA to separate plasma and peripheral blood mononuclear cells (PBMC). Density gradient centrifugation was used to isolate PBMC. Serum samples were also collected (10 mL/cow) on d -3, 0, 14. Cells were incubated with propidium iodide and antibody surface cell markers for CD4, CD8, CD25, CD14, CD86, and CD335. An Amnis FlowSight flow cytometer was used to determine the percentage of each cell type in the PBMC. Concentrations of antibodies for BVDV and IBR were determined in serum samples collected pre-vaccination (d -3 and 0) and on d 14. Differences in antibody titers and leukocyte populations were analyzed as repeated measures using the MIXED model procedure in SAS. There were no differences in IBR (P = 0.2) or BVDV (P = 0.47) antibody concentrations between seasons. Percentage of antigen presenting cells (CD14+) was greater in the Summer compared with the Fall (P = 0.01; Summer=11.7 ± 1%; Fall = 7.3 ± 1.1%), but natural killer cells (CD335+) were greater in the Fall compared with the Summer (P = 0.002; Summer = 0.6 ± 0.6%; Fall = 4.4±0.7%). There was a significant treatment by time interaction for antigen presenting cells (P = 0.04), T-helper cells (CD4+; P = 0.01), activated T-helper cells (CD4+CD25+; P ≤ 0.0001), activated cytotoxic T-cells (CD8+CD25+; P = 0.03), activated T-cells (CD25+; P ≤ 0.0001), and natural killer cells (P ≤ 0.0001), but there was no difference between seasons in activated antigen presenting cells (CD14+CD86+; P = 0.19). From pre-vaccination to d 14, natural killer cells were elevated during the Fall compared with the Summer on all days (P = 0.04). Antigen presenting cells were greater in the Summer compared with the Fall on d 4, 10 and 14 (P < 0.02). T-helper cells, activated T-helper cells, activated cytotoxic T-cells, and activated T-cells increased post-vaccination in the Fall, but did not change during the Summer. Thus, ambient temperature (summer vs fall) did not directly impact production of antibodies for IBR or BVDV but did induce changes in specific immune cells following vaccination.