W. G. Van Alstine

Dietary polyunsaturated fatty acid effects on immune cells of the porcine lung.

The effects of various dietary polyunsaturated fatty acids (PUFAs) on the function of immune cells of the porcine lung was studied. Groups of six pigs were fed diets containing 10.5% corn oil [CO; enriched in linoleic acid (18:2, n‐6)], linseed oil (LO; enriched in α‐linolenic acid (18:3, n‐3)], menhaden oil (MO; enriched in eicosapentaenoic (20:5; n‐3) and docosahexaenoic (22:6; n‐3) acids], linseed + corn oil (1:1; LC), and menhaden + corn oil (1:1; MC) for 28–30 days. Basal levels of alveolar macrophage (mφ) tumor necrosis factor‐α (TNF‐α) production were higher (P < .05) for LC‐ and MC‐fed pigs than for CO‐ and LO‐fed pigs. Lipopolysaccharide (LPS)‐stimulated LC and MC mφs produced more TNF than mφs from pigs fed CO, LO, and MO diets. Macrophages from pigs receiving the CO and LC diets had higher (P < .05) levels of leucine aminopeptidase than mfs from the other dietary groups. Lipopolysaccharide did not increase mφ nitrite production over basal levels except in the MO diet group. However, LPS‐stimulated mφs from the CO, MO, and LC dietary groups produced more nitrite than mfs from MC‐fed pigs. Alveolar lymphocytes from pigs receiving the MC diet produced more T cell growth factors than LO and MO mφs. Alveolar mφs from the different dietary groups did not differ in their capacity for non‐immune‐mediated phagocytosis of fluorescent latex beads. These results indicate that dietary PUFAs can modulate some functions of porcine alveolar immune cells and that this may prove significant for host response to respiratory disease agents. J. Leukoc. Biol. 56: 599–604; 1994.

Porcine reproductive and respiratory syndrome virus does not exacerbate Mycoplasma hyopneumoniae infection in young pigs

The purpose of this study was to determine if Porcine Reproductive and Respiratory Syndrome (PRRS) virus infection altered the severity of acute Mycoplasma hyopneumoniae (MH) infection in young pigs. Twenty five, 3-week-old male pigs were randomly assigned by litter and weight to one of 3 groups. Groups 1 (PRRS only, n = 5) and 2 (PRRS + MH, n = 10) were inoculated intranasally with PRRS virus (IN-5 isolate, 10(5) TCID50) and viremia in all pigs was confirmed by virus isolation from serum 3 days later. Group 3 (MH only, n = 10) was inoculated at the same time with virus free culture media. Seven days after virus inoculation, Groups 2 and 3 were inoculated intratracheally with MH (strain P-5722-3, 10(7) CCU). All pigs were euthanized and necropsied 28 days later, when maximum lesions of mycoplasmosis occurs. Pigs in group 1 did not cough and had no gross lung lesions, but were still viremic at necropsy. MH was isolated from all pigs in groups 2 (avg. log 5.2 +/- 1.3) and 3 (avg. log 5.1 +/- 1.5), but differences were not significant (P = 0.87). Similarly, there were no differences in average days coughing (8.9 +/- 2.8 v 11.2 +/- 4.5, P = 0.17), grossly pneumonic lung (16.5% v 17%, P = 0.91), or microscopic lung lesion scores (10.1 +/- 2.6 v 11.1 +/- 1.9, P = 0.35) between pigs in groups 2 and 3. Under these experimental conditions, PRRS virus infection did not increase the severity of experimental Mycoplasma hyopneumoniae infection in young pigs.

Expression of inflammatory cytokines and Toll-like receptors in the brain and respiratory tract of pigs infected with porcine reproductive and respiratory syndrome virus

The objective of this experiment was to evaluate the central and peripheral expression of selected pro-inflammatory cytokines and Toll-like receptors (TLRs) in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Twenty-four 8-week-old pigs were inoculated with either sterile medium or PRRSV. Pigs were monitored 14d after inoculation and then euthanized for tissue sample collection. PRRSV was detected in serum, lung and brain tissue of pigs given PRRSV but not in any tissue of pigs given medium. Infection with PRRSV increased serum levels of IL-1beta, IL-6, TNFalpha, and IFNgamma and elicited a mild transient fever and reduced growth performance. Infection by PRRSV also increased mRNA for the pro-inflammatory cytokines as well as mRNA for TLR3, TLR4, and TLR7 in the tracheobronchial lymph nodes. The TLR3, TLR4, TLR7 and most of the pro-inflammatory genes also were up-regulated in discrete brain areas of PRRSV-infected pigs. Collectively, the results indicate that following inoculation, PRRSV is present in the periphery and brain and that infection is associated with a peripheral and central pro-inflammatory response, fever, and reduced growth performance. The findings are interpreted to suggest the innate immune system of the brain is responsive to PRRSV infection.

Mannan oligosaccharide improves immune responses and growth efficiency of nursery pigs experimentally infected with porcine reproductive and respiratory syndrome virus

This study was conducted to determine whether the ingestion of mannan oligosaccharide (MOS, Bio-Mos) alters the immune response of nursery pigs challenged with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 64 pigs (3 wk old), free of PRRSV, were used in 2 separate but similar experiments conducted sequentially. Pigs were blocked by initial BW. Sex and ancestry were equalized across treatments. Pigs were randomly assigned from within blocks to 1 of 4 treatments in a 2 × 2 factorial arrangement [2 types of diet: control (0%) and MOS addition (0.2%); 2 levels of PRRSV: with and without]. There were 8 replicate chambers of 2 pigs each. After 2 wk of a 4-wk period of feeding the treatments, pigs were intranasally inoculated with PRRSV or a sterile medium at 5 wk of age. The PRRSV challenge decreased ADG, ADFI, and G:F throughout the experiment (P < 0.001). Feeding MOS improved G:F of the pigs during d 7 to 14 (P=0.041) postinfection (PI). Serum concentrations of tumor necrosis factor (TNF)-α, C-reactive protein, and haptoglobin were increased by PRRSV (P < 0.001). The MOS × PRRSV interaction was significant for TNF-α at d 14 PI (P=0.028), suggesting that infected pigs fed MOS had less TNF-α than those fed the control. Dietary MOS increased serum IL-10 at d 14 PI (P=0.036). Further, MOS-fed pigs had greater numbers of white blood cells (WBC) at d 3 (P=0.048) and 7 PI (P=0.042) and lymphocytes at d 7 PI (P=0.023) than control-fed pigs. In contrast, PRRSV decreased (P < 0.01) WBC numbers until d 14 PI. Dietary MOS appeared (P=0.060) to increase the neutrophils in PRRSV-infected pigs at d 3 PI, but no (P=0.202) MOS × PRRSV interaction was found. Infection with PRRSV increased rectal temperature (RT) of pigs at d 3 PI (P < 0.001) and continued to affect the infected pigs fed the control diet until d 14 PI. The MOS × PRRSV interaction for RT was found at d 7 (P < 0.01) and 10 (P=0.098) PI, indicating that the infected pigs fed MOS had a decreased RT compared with those fed the control. This could explain why feed efficiency was improved by MOS. No effect (P > 0.05) of treatments on viremia or PRRSV-specific antibody was observed. These results suggest that MOS is associated with rapidly increased numbers of WBC at the early stage of infection and alleviates PRRSV-induced effects on G:F and fever. The results also indicate that the reduced intensity of inflammation by MOS may be related to changes in inflammatory mediator levels at the end of the acute phase.

Mannan oligosaccharide increases serum concentrations of antibodies and inflammatory mediators in weanling pigs experimentally infected with porcine reproductive and respiratory syndrome virus.

ABSTRACT Mannan-containing products are capable of modulating immune responses in animals. However, different products may have diverse immunomodulation. The experiment was conducted to examine effects of mannan oligosaccharide (Actigen; ACT) on growth performance and serum concentrations of antibodies and inflammatory mediators in weanling pigs (Sus scrofa) experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 32 PRRSV-negative pigs (3 wk old) were randomly assigned from within blocks to 1 of 4 treatments in a 2 by 2 factorial arrangement [2 types of diet: control (0%) and ACT addition (0.04%); and with and without PRRSV] in a randomized complete block design. Pigs were blocked by initial BW within sex. Ancestry was equalized across treatments. Pigs (8/treatment) were kept individually in each pen. After 2 wk of an 8-wk period of feeding the treatments, pigs received an intranasal inoculation of PRRSV or sham medium at 5 wk of age. Infection by PRRSV decreased ADG, ADFI, and G:F throughout the experiment (P < 0.01). Actigen did not affect ADG (P = 0.450), but decreased (P = 0.047) ADFI from 28 to 42 days postinoculation (DPI). During that time, ACT improved G:F in infected pigs but not in sham controls (interaction, P = 0.009). Dietary ACT did not affect viremia in infected pigs (P > 0.05), but increased PRRSV-specific antibody titer at 35 DPI (P = 0.042). Infection with PRRSV induced the febrile responses of pigs from 3 to 10 DPI (P < 0.001) with return to normal at 14 DPI. During the experimental period, the rectal temperature of pigs was found slightly elevated by ACT (P = 0.045). Infected pigs had greater serum concentrations of IL-1β, tumor necrosis factor (TNF)-α, IL-12, interferon (IFN)-γ, IL-10, and haptoglobin (Hp) than sham controls (P < 0.001). These results indicate that PRRSV stimulated secretion of cytokines involved in innate, T-helper 1, and T-regulatory immune responses. Actigen tended to decrease the serum TNF-α concentration regardless of PRRSV (P = 0.058). The ACT × PRRSV interaction was significant for IL-1β (P = 0.016), IL-12 (P = 0.026), and Hp (P = 0.047), suggesting that infected pigs fed ACT had greater serum concentrations of these mediators than those fed the control. The increases in IL-1β and IL-12 may favorably promote innate and T-cell immune functions in infected pigs fed ACT. Feeding ACT may be useful as ACT is related to increased PRRSV antibody titers and G:F in infected pigs at certain times during infection.

Dietary plant extracts improve immune responses and growth efficiency of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

A study was conducted to evaluate the effects of 3 different plant extracts on growth performance and immune responses of weaned pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). A total of 64 weaned pigs (7.8 ± 0.3 kg BW), free of PRRSV, were randomly allotted to 1 of 8 treatments in a 2 × 4 factorial arrangement with a randomized complete block design. Pigs were blocked by initial BW. Sex and ancestry were equalized across treatments. The first factor was with or without PRRSV challenge (intranasal dose; 10(5) 50% tissue culture infective dose). The second factor was represented by 4 diets: a nursery basal diet (CON), 10 mg/kg capsicum oleoresin (CAP), garlic botanical (GAR), or turmeric oleoresin (TUR). Pigs were housed in disease containment chambers for 28 d [14 d before and after the inoculation (d 0)]. Blood was collected on d 0, 7, and 14 to measure the total and differential white blood cells (WBC), and serum was collected to measure viral load by quantitative PCR, PRRSV antibody titer, tumor necrosis factor-α (TNF-α), IL-1β, C-reactive protein (CRP), and haptoglobin (Hp) by ELISA. In the unchallenged group, all piglets were PRRSV negative during the overall period postinoculation. All data were analyzed using PROC MIXED of SAS. The PRRSV challenge decreased (P < 0.01) ADG, ADFI, and G:F from d 0 to 14. Feeding TUR improved G:F of the PRRSV-infected pigs from d 0 to 14. The numbers of WBC and neutrophils were decreased (P < 0.05) by PRRSV on d 7 but increased (P < 0.05) by PRRSV on d 14, indicating the PRRSV-infected pigs undergo a stage of weak immune responses. Feeding GAR increased (P < 0.05) B cells and CD8+ T cells of PRRSV-infected pigs compared with the CON. Furthermore, the PRRSV challenge increased (P < 0.05) serum viral load, TNF-α, and IL-1β on d 7 and serum viral load, CRP, and Hp on d 14, but feeding plant extracts to PRRSV-infected pigs reversed (P < 0.05) this increase. Infection with PRRSV increased (P < 0.05) rectal temperature of pigs on d 7, 9, and 11, but PRRSV-infected pigs fed plant extracts had lower rectal temperature (P < 0.05) than pigs fed the CON, indicating feeding plant extracts delayed the fever caused by PRRSV infection. In conclusion, results indicate that supplementation with plant extracts reduces the adverse effects of PRRSV by improving the immune responses of pigs, and the 3 plant extracts tested here show different effects. Supplementation with TUR improved feed efficiency of pigs challenged with PRRSV.

Mannan oligosaccharide modulates gene expression profile in pigs experimentally infected with porcine reproductive and respiratory syndrome virus

This study characterized gene expression in peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage fluid (BALF) cells from control- or mannan oligosaccharide (MOS)-fed pigs with or without porcine reproductive and respiratory syndrome virus (PRRSV) at d 7 postinfection (PI). Weaned pigs (3 wk old) fed 0 or 0.2% MOS (Bio-Mos) diets were intranasally inoculated with PRRSV or a sterile medium at 5 wk of age. Total RNA (3 pigs/treatment) was extracted from cells. Double-stranded cDNA was amplified, labeled, and further hybridized to the Affymetrix GeneChip Porcine Genome Array consisting of 23,937 probe sets representing 20,201 genes. Microarray data were analyzed in R using packages from the Bioconductor project. Differential gene expression was tested by fitting a mixed linear model equivalent to a 2 × 2 factorial ANOVA using the limma package. Dietary MOS and PRRSV changed the expression of thousands of probe sets in PBMC and BALF cells (P < 0.05). The MOS × PRRSV interaction altered the expression of more nonimmune probe sets in PBMC (977 up, 1,128 down) than in BALF cells (117 up, 78 down). The MOS × PRRSV interaction (P < 0.05) for immune probe sets in PBMC affected genes encoding key inflammatory mediators. In uninfected pigs, gene expression of IL-1α, IL-6, myeloid differentiation factor 88, Toll-like receptor (TLR) 4, major histocompatibility complex (MHC) II, and dead box polypeptide 58 increased in PBMC of MOS-fed pigs (P < 0.05). This suggests that MOS enhances disease resistance in pigs and supports the fact that MOS induced a rapid increase in leukocytes at d 3 and 7 PI. Within infected pigs, however, MOS reduced the expression of IL-1β, IL-6, IL-8, macrophage inflammatory protein (MIP)-1α, MIP-1β, monocyte chemotactic protein (MCP)-1, and TLR4 genes in PBMC (P < 0.05). This finding may explain why fever was ameliorated in infected pigs fed MOS by d 7 PI. The expression of IL-1β, IL-6, MIP-1β, MCP-1, and TLR4 genes was confirmed by quantitative real-time reverse-transcription PCR. In BALF cells of infected pigs, MOS reduced the gene expression of TLR4, MHCII, and molecules associated with the complement system, but increased the gene expression of MHCI. In short, MOS regulated the expression of nonimmune and immune genes in pig leukocytes, perhaps providing benefits by enhancing the immune responses of the pigs to an infection, while preventing overstimulation of the immune system.

Effects of dietary soybean meal concentration on growth and immune response of pigs infected with porcine reproductive and respiratory syndrome virus

An experiment was conducted to determine the effects of dietary soybean meal (SBM) concentration on the growth performance and immune response of pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Four experimental treatments included a 2 × 2 factorial arrangement of 2 dietary SBM concentrations, 17.5% (LSBM) or 29% (HSBM), and 2 levels of PRRSV infection, uninfected sham or PRRSV infected. Sixty-four weanling pigs of split sex (21 d of age, 7.14 ± 0.54 kg) were individually housed in disease containment chambers. Pigs were provided a common diet for 1 wk postweaning before being equalized for BW and sex and allotted to 4 treatment groups with 16 replicate pigs per group. Pigs were fed experimental diets for 1 wk before receiving either a sham inoculation (sterile PBS) or a 1 × 10 50% tissue culture infective dose of PRRSV at 35 d of age (0 d postinoculation, DPI). Pig BW and feed intake were recorded weekly, and rectal temperatures were measured daily beginning on 0 DPI. Blood was collected on 0, 3, 7, and 14 DPI for determination of serum PRRSV load, differential complete blood cell counts, and haptoglobin and cytokine concentrations. Infection with PRRSV increased (P < 0.01) rectal temperatures of pigs throughout the infection period, with no influence of dietary SBM concentration. Pigs in the PRRSV-infected group had lower (P < 0.01) ADFI and G:F from 0 to 14 DPI compared with uninfected pigs. In the PRRSV-infected group, pigs fed HSBM tended to have improved ADG (P = 0.06) compared with pigs fed LSBM, whereas there was no influence of SBM concentration on growth of pigs in the uninfected group. At 14 DPI, PRRSV-infected pigs fed HSBM had a lower serum PRRSV load (P < 0.05), a higher (P = 0.02) hematocrit value, and a tendency for greater hemoglobin concentration (P = 0.09) compared with pigs fed LSBM. Serum haptoglobin and tumor necrosis factor-α concentrations of PRRSV-infected pigs were lower (P < 0.05) in pigs fed HSBM at 3 and 14 DPI, respectively, than in pigs fed LSBM. Overall, increasing the dietary SBM concentration modulated the immune response and tended to improve the growth of nursery pigs during a PRRSV infection.