Changes in leukocyte subsets of pregnant gilts experimentally infected with porcine reproductive and respiratory syndrome virus and relationships with viral load and fetal outcome

Abstract

In spite of more than two decades of extensive research, the understanding of porcine reproductive and respiratory syndrome virus (PRRSv) immunity is still incomplete. A PRRSv infection of the late term pregnant female can result in abortions, early farrowings, fetal death, and the birth of weak, congenitally infected piglets. The objectives of the present study were to investigate changes in peripheral blood mononuclear cell populations in third trimester pregnant females infected with type 2 PRRSv (NVSL 97-7895) and to analyze potential relationships with viral load and fetal mortality rate. PRRSv infection caused a massive, acute drop in total leukocyte counts affecting all PBMC populations by two days post infection. Except for B cells, cell counts started to rebound by day six post infection. Our data also show a greater decrease of naïve B cells, T-helper cells and cytolytic T cells than their respective effector or memory counterparts. Absolute numbers of T cells and γδ T cells were negatively associated with PRRSv RNA concentration in gilt serum over time. Additionally, absolute numbers of T helper cells may be predictive of fetal mortality rate. The preceding three leukocyte populations may therefore be predictive of PRRSv-related pathological outcomes in pregnant gilts. Although many questions regarding the immune responses remain unanswered, these findings provide insight and clues that may help reduce the impact of PRRSv in pregnant gilts.

Figure 1

Changes in total leukocyte counts in response to PRRSv infection in pregnant gilts. Mean (+SD) total leukocyte counts are presented from 111 INOC and 19 CTRL gilts for the respective study days. Superscript letters indicate significant differences (P < 0.001) between INOC and CTRL gilts and between study days within each treatment group.

Figure 2

Changes in monocytes in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for monocytes (CD172α^highCD4⁻CD14⁺) is demonstrated using representative data from gilt #53. B) Line chart: Changes in absolute numbers (mean ± SD) of monocytes (orange) are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days. C) Bar chart: The mean percentages (+SD) of CD172a^highCD4⁻CD14⁺ PBMC from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts.

Figure 3

Changes in NK cells in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for NK cells (CD3⁻CD8α⁺) is demonstrated using representative data from gilt #53. B) Line chart: Changes in absolute numbers (mean ± SD) of NK cells are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days.

Figure 4

Changes in B cells in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for B cells (CD79α⁺) and CD21-defined subpopulations is demonstrated using representative data from gilt #53. B-D) Line charts: Changes in absolute numbers (mean ± SD) of total B cells (turquois), CD21⁻ (purple), and CD21⁺ (pink) B cells are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days. E) Bar chart: The mean percentages (+SD) of B cells expressing CD21 within total CD79α⁺ B cells from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts.

Figure 5

Changes in T cells in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for T cells (CD3⁺) is demonstrated using representative data from gilt #53. B) Line chart: Changes in absolute numbers (mean ± SD) of T cells are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days.

Figure 6

Changes in γδ T cells in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for γδ T cells and CD2/CD8α defined subpopulations is demonstrated using representative data from gilt #53. B-E) Line charts: Changes in absolute numbers (mean ± SD) of total γδ T cells (blue), CD2⁻CD8α⁻ γδ T cells (orange), CD2⁻CD8α⁺ γδ T cells (purple), and CD2⁺CD8α⁺ γδ T cells (green) are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days. F-H) Bar charts: The mean percentages (+SD) of CD2⁻CD8α⁻ γδ T cells (orange), CD2⁻CD8α⁺ γδ T cells (purple), and CD2⁺CD8α⁺ γδ T cells (green) within total γδ T cells from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts.

Figure 7

Changes in T helper cells in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for T helper cells (CD4⁺) and CD8α-defined subpopulations is demonstrated using representative data from gilt #53. B-D) Line charts: Changes in absolute numbers (mean ± SD) of total T helper cells (yellow), CD8α⁻ T helper cells (light blue), and CD8α⁺ T helper cells (brown) are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days. E) Bar chart: The mean percentages (+SD) of T helper cells expressing CD8α within total CD4⁺ T cells from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts.

Figure 8

Changes in CTLs in response to PRRSv infection in pregnant gilts. A) Dot plots: The gating strategy for CTLs (CD3⁺CD8β⁺) and SLA-DR-defined subpopulations is demonstrated using representative data from gilt #53. B-C) Line charts: Changes in absolute numbers (mean ± SD) of total CTLs (blue) and SLA-DR⁺ CTLs (red) are presented from 111 INOC and 19 CTRL gilts over time. P-values indicate significant differences between INOC and CTRL gilts on individual days. D) Bar chart: The mean percentages (+SD) of CTLs expressing SLA-DR within total CTLs from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts. E-F) Bar charts: The MFIs of CD8β and SLA-DR on CTLs from INOC and CTRL gilts are presented for the respective study days. Superscript letters indicate significant differences (P < 0.01) between study days within INOC or CTRL gilts.