Swine Alveolar Macrophages Research Articles

213 ASSESSMENT OF THE SUSCEPTIBILITY OF PORCINE PRE-IMPLANTATION EMBRYOS TO PSEUDORABIES VIRUS (PRV) AND PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS (PRRSV) USING SUBZONAL MICROINJECTION

It is known that porcine pre-implantation embryos before the morula stage are refractory to infection with pseudorabies virus (PRV) and porcine reproductive and respiratory syndrome virus (PRRSV) (Bolin et al. 1981 Am. J. Vet. Res. 42, 1711-1712; Prieto et al. 1996 Theriogenology 46, 687-693, respectively). The effects of PRV and PRRSV on embryonic cells of morulae and blastocysts are unknown. Therefore, the objectives of the present study were to (1) assess the effects of PRV and PRRSV exposure on further embryo development, and (2) determine whether PRV and PRRSV are able to replicate in embryonic cells. Zona pellucida (ZP)-intact morulae (6 days post-insemination, 6 dpi) and early blastocysts (7 dpi) were microinjected subzonally with approximately 3 nL of 109 TCID50/mL PRV (strain 89v87, second passage in swine testicle cells) or 108.6 TCID50/mL PRRSV (Lelystad virus strain, 13th passage in swine alveolar macrophages). Control embryos were microinjected under the same circumstances with phosphate-buffered saline (PBS). Hatched blastocysts (8 dpi) were exposed for 1 h at 39�C to 105 TCID50/mL of PRV or PRRSV of the same strains used for injecting earlier embryonic stages. Control hatched blastocysts were incubated with PBS. Each group of morulae and blastocysts consisted of approximately 20 embryos. Embryonic development was assessed every 12 h. At 48 h post injection, the percentage of infected embryos and the percentage of viral antigen positive cells per embryo were determined by immunofluorescence. Subzonal microinjection of ZP-intact morulae and blastocysts with PRV inhibited in vitro development in comparison to the controls. Moreover, under direct immunofluorescence, PRV antigen-positive cells were detected in association with the embryos. Exposure of hatched blastocysts to PRV inhibited further embryo development; the majority (16/20) of the embryos degenerated 24 h after incubation. Perivitelline microinjection of ZP-intact morulae and blastocysts with PRRSV and incubation of hatched blastocysts with PRRSV did not inhibit in vitro development in comparison to the controls. No PRRSV antigen positive cells were detected in association with the embryos. Based on these results, it can be deduced that embryonic cells of morulae and blastocysts are susceptible to PRV infection but refractory to PRRSV infection. Another argument substantiating insusceptibility of embryos to certain viral pathogens is the demonstration of the lack of virus receptors at a given embryonic cell stage. Therefore, the expression of sialoadhesin, the receptor that mediates the internalization of PRRSV in cells, was investigated in hatched blastocysts (n = 10). By indirect immunofluorescence using monoclonal antibody 41D3 directed against porcine sialoadhesin, no positive signals were detected. The result of this experiment strengthens the statement that embryonic stages up to the hatched blastocyst stage are refractory to PRRSV infection.

The effect of recombinant swine interleukin-4 on swine immune cells and on pro-inflammatory cytokine productions in pigs

The in vitro effect and the in vivo influence of recombinant swine IL-4 (rSwIL-4) were characterized in various swine cells and in nursery pigs on LPS-induced endotoxic shock and pro-inflammatory cytokine productions. In in vitro experiment, the rSwIL-4 induced a proliferation of CD4 positive T cells in mitogen-prestimulated peripheral blood mononuclear cell (PBMC). In addition, the rSwIL-4, which was produced from insect cells, promoted the differentiation of monocytes into immature dendritic cells in combination with granulocyte macrophage-colony stimulating factor (GM-CSF). Furthermore, the rSwIL-4 successfully suppressed the LPS-induced secretion of TNF-α, IL-1α, IL-6, IL-8, and IL-18 from swine alveolar macrophages when rSwIL-4 was treated at the same time with LPS. In in vivo experiment in nursery pigs, subcutaneous pretreatment of rSwIL-4, which was produced from baculovirus expression system, enhanced the severity of respiratory failure with endotoxic shock, and increased the production of TNF-α and IL-18 in response to inoculation with LPS. These results indicate that the rSwIL-4 is biologically active in both in vitro and in vivo treatments. Depending on the administration time, pro-inflammatory cytokine productions by IL-4 can cause either inhibitory or stimulatory regulation.

197SUSCEPTIBILITY OF PORCINE MORULAE AND BLASTOCYST STAGE EMBRYOS TO PSEUDORABIES VIRUS AND PORCINE REPRODUCTIVE AND RESPIRATORY SYNDROME VIRUS

Porcine preimplantation embryos are refractory to infection with pseudorabies virus (PRV) and porcine reproductive and respiratory syndrome virus (PRRSV) during the 2–4 to 16-cell stage as described by Bolin et al. (1981 Am. J. Vet. Res. 42: 1711–1712) and Prieto et al. (1996 Theriogenology 46: 687–693), respectively. Research on the effects of PRV and PRRSV on embryonic cells of morulae, blastocysts and hatched blastocysts is limited. Therefore, the objectives of the present study were (i) to assess the effects of PRV and PRRSV exposure on further embryonic development, and (ii) to determine whether PRV and PRRSV are able to replicate in embryonic cells of porcine morulae and blastocysts. In vivo produced ZP-intact and ZP-free morulae (6 days post-insemination), early blastocysts (7 days post-insemination), and hatched blastocysts (8 days post-insemination) derived from 22 superovulated sows were exposed to 105 TCID50 PRV (strain 89v87, second passage in swine testicle cells) or to 105 TCID50 PRRSV (Lelystad virus strain, 13th passage in swine alveolar macrophages) for 1h at 39°C. Control embryos were incubated under the same circumstances without viruses. Each group of morulae and blastocysts consisted of approximately 20 embryos. Embryonic development was assessed every 12h and differences in rates of development were analyzed using Chi-square analysis or Fisher’s exact test. At 48h post-incubation, embryos were collected and examined for viral antigen by indirect immunofluorescence. Further embryo development of ZP-intact and ZP-free morulae and blastocysts was not affected by exposure to PRV or PRRSV compared to controls (P<0.05). Moreover, using indirect immunofluorescence, no PRV or PRRSV antigen-positive cells were detected. Exposure of hatched blastocysts to PRV inhibited further embryo development as 100% (n=5) of the embryos degenerated 24h after viral exposure. This was significantly different (P<0.05) from the controls and the PRRSV-incubated hatched blastocysts that did not experience any negative influence on embryo development. Based on these results it can be concluded that embryonic cells are not susceptible to a PRRSV infection up to the hatched blastocyst stage. Embryonic cells of morulae and blastocysts are refractory to PRV, but the virus has a detrimental effect on further embryo development of hatched blastocysts. More experiments are necessary to confirm these results and to investigate whether, or at which preimplantation stage, embryos are susceptible to a PRRSV infection.

The effects of mycotoxins, fumonisin B1 and aflatoxin B1, on primary swine alveolar macrophages.

Mycotoxins were fungal metabolites that were widely present in feed and food; some of them were known to associate with human and animal disease. In the present study, the effects of fumonisin B1 (FmB1) and aflatoxin B1 (AFB1) on swine alveolar macrophages (AM) were examined by exposing primary cultures of swine AM to various concentrations of mycotoxins. Incubation of AM with 5 microg/ml of FmB1 for 72 h led to a reduction in the number of viable cells to 65% of the control levels. In the presence of 1.5 microg/ml of AFB1, the viability of AM falls to less than 41% of controls after 24 h exposure. FmB1, but not AFB1, induced the apoptosis of swine AM with evidence of DNA laddering and nuclear fragmentation. However, both FmB1 and AFB1 exposure induced the expression of apoptosis-related heat shock protein 72 (HSP 72) in AM. Swine AM treated with 50 ng/ml of FmB1 and 100 ng/ml of AFB1 for 24 h led to a reduction in phagocytic ability to approximately 55 and 36% of the control levels, respectively. Incubation of AM with FmB1 (2 and 10 microg/ml) for 24 h dramatically decreased the mRNA levels of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha). However, AFB1 treatment did not affect the expression of IL-1beta and TNF-alpha mRNA. The results suggest that both FmB1 and AFB1 are immunotoxic to swine AM but that they exert their toxic effects via different biochemical mechanisms.

GENERATION AND MAPPING OF EXPRESSED SEQUENCE TAGS FROM VIRUS-INFECTED SWINE MACROPHAGES

In an effort to identify genes that have a major effect on macrophage function during viral infection, we employed differential display reverse transcription (DDRT)-PCR to capture expressed sequence tags (ESTs) of swine alveolar macrophages infected by the porcine reproductive and respiratory syndrome virus (PRRSV). Sequence analyses showed that approximately 60% of these ESTs had significant similarity (≥93%) to known pig ESTs or genes or matched sequences from other species with homology ≥80%. To determine chromosomal localization, PCR-based mapping was performed across either swine somatic cell hybrid or radiation hybrid panels. A total of 48 porcine viral response ESTs were mapped via the swine somatic cell panel or the INRA-Minnesota porcine Radiation Hybrid (IMpRH) panel (LOD > 6.0). Northern blot analyses confirmed PRRSV-induced altered transcript expression for several ESTs, including a 2′–5′ oligoadenylate synthetase and a putative dual-specificity phosphatase. These virus-response ESTs represent good candidate genes for understanding PRRSV pathogenesis and for dissecting host genes which may have major effect on disease resistance.

Effect of temperature modulation and bvg mutation of Bordetella bronchiseptica on adhesion, intracellular survival and cytotoxicity for swine alveolar macrophages

Bordetella bronchiseptica causes respiratory disease in swine, yet there are no studies examining the interaction of B. bronchiseptica with swine alveolar macrophages. A swine isolate of B. bronchiseptica was able to adhere to, and survive intracellularly in, swine alveolar macrophages, but the relative ability of the bacteria to accomplish these functions was dependent on its phenotypic phase and culture conditions. More bacteria were observed extracellularly as well as intracellularly by immunofluorescent staining when B. bronchiseptica was cultured at 23°C as compared to 37°C. However, more bacteria cultured at 37°C were found surviving intracellularly after the macrophages were cultured with polymyxin B to kill extracellular bacteria. Similar results were seen in experiments performed with an isogenic Bvg − phase-locked mutant of B. bronchiseptica cultured at 37 or 23°C, indicating that another temperature dependent mechanism in addition to bvg may play a role in adhesion and intracellular survival . B. bronchiseptica was cytotoxic for swine alveolar macrophages in the Bvg + phase only. The cytotoxicity of B. bronchiseptica for alveolar macrophages, and its ability to survive phagocytosis, are no doubt important to escape from immune clearance mechanisms and establish infection, and could leave the host susceptible to secondary respiratory pathogens.

Ultrastructural pathogenesis of the PRRS virus

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) was first isolated in swine alveolar macrophages (SAMs) and has subsequently been reported to replicate in other cell lines. Entry of the virus inside the cell takes place by receptor-mediated endocytosis. Following the entry of the virus into the cell, several not completely understood changes take place. PRRSV has been reported to be an apoptotic-inductor virus both in vivo and in vitro. Interestingly, it has been suggested that PRRSV-induced apoptosis occurs in cells other than those in which PRRSV replicates by a bystander mechanism. In this paper the ultrastructural pathogenesis of PRRSV will be reviewed.

In vivo Replication of Porcine Reproductive and Respiratory Syndrome Virus in Swine Alveolar Macrophages and Change in the Cell Population in Bronchoalveolar Lavage Fluid after Infection.

Replication of porcine reproductive and respiratory syndrome (PRRS) virus in swine alveolar macrophages (AM) and cell population in broncho-alveolar lavage fluid (BALF) obtained from PRRS virus-infected pigs were investigated. BALF samples were periodically collected from 6 pigs infected with PRRS virus and 3 non-inoculated control pigs by means of fiber-optic bronchoscope between post-inoculation day (PID) 0 and 56. The mean ratio of macrophages in BALF collected from infected group was 92.7 +/- 3.2% before inoculation and gradually decreased from PID 14. On the other hand, the ratio of lymphocytes was 4.8 +/- 3.2% before inoculation and increased from PID 21 and indicated 41.8 +/- 9.1% on PID 28. After that, they decreased gradually and that of macrophages correspondingly increased. The ratio of neutrophils maintained between 0.7% and 5.1%. The ratios of macrophages, lymphocytes and neutrophils collected from control group were almost stable through the examination. Intracellular PRRS virus antigens in AM were detected from PID 2 by indirect immunofluorescence assay (IIFA). PRRS virus was first isolated from BALF samples collected from inoculated group between PID 2 and 49. From serum, virus was isolated between PID 2 and 21. Antibodies in sera measured by IIFA to PRRS virus were first detected on PID 14 and the antibody titer rose to 1:640 or 1:1,280. The results suggested that PRRS virus replicates in swine AM for a relatively long period.

Effect of porcine reproductive and respiratory syndrome virus (PRRSV) on development of porcine fertilizedova in vitro

Fertilized pig ova, collected from 14 estrus-synchronized gilts 32 h after presumed ovulation were microinjected or cultured for 72 h in Beltsville Embryo Culture Medium-3 with or without Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). To detect virus in the samples, virus isolation of swine alveolar macrophage, Reverse Transcriptase Polymerase Chain Reaction and Fluorescent Antibody techniques were employed. Microinjection or incubation of embryos with PRRSV did not significantly inhibit development of the porcine embryos in vitro when compared with that of controls (P = 0.75 and P = 0.14, respectively). Although either 10 to 20 TCID 50 were microinjected or large concentrations of virus were used for embryo exposure by incubation, PRRSV was not detected in association with the embryos. It is concluded based on the experiments reported here that 4- to 16-cell stage pig embryos are not susceptible to productive infection with PRRSV in vitro.

Serological property and replication in cell cultures of porcine reproductive and respiratory syndrome viruses isolated in Japan.

The serological property and replication in swine alveolar macrophages (SAM) and MARC-145 cell cultures of 35 porcine reproductive and respiratory syndrome (PRRS) viruses isolated in SAM were investigated. All the isolates were reacted almost equally with antisera against three Japanese isolates including EDRD-1 strain (American type) in immunoperoxidase monolayer assay (IPMA), but weakly or did not react with antiserum against Lelystad virus (European type) indicating that the Japanese isolates are more closely related to an American type virus. Twenty two of 35 isolates replicated with CPE both in SAM and MARC-145 cells, whereas remaining 13 isolates did not show CPE in MARC-145 cells. The antigenicity of the isolates did not relate to the virus origin and the replication in the cell cultures.

Semen changes in boars after experimental infection with porcine reproductive and respiratory syndrome (PRRS) virus

Eleven boars seronegative to porcine reproductive and respiratory syndrome virus (PRRSV) were trained for semen collection: five boars were inoculated intranasally with 6 × 10 6TCID 50/ml of PRRSV (Group A); four boars were inoculated intranasally with 6 × 10 4TCID 50/ml (Group B); and two boars were used as uninfected control (Group C). Semen samples were collected at 7-d intervals from 49 d prior to experimental inoculation with PRRSV to 70 d after inoculation, and were examined for sperm volume, sperm concentration, sperm morphology, sperm motility and for the presence of PRRSV. The infection in boars was demonstrated by the reisolation of PRRSV from the serum of all inoculated boars. Rectal temperatures and general health of the boars were clinically normal throughout the trial. Differences were observed in the quality of semen collected from boars after experimental infection with PRRSV. This infection induced a significant decrease in sperm motility and in spermatozoa with normal acrosomes. Of the semen samples tested for virus isolation in swine alveolar macrophages PRRSV was only isolated in 1 boar from Group B. The virus was detected in an additional semen sample in Group A by the production of an antibody titer in a biological assay. All attempts to detect PRRSV by RT-PCR in semen samples were unsuccessful. Nevertheless, from our study it is possible to suggest that the PRRSV can occasionally be transmitted in the semen during the initial phase of the disease.

豚からの豚繁殖・呼吸障害症候群ウイルスの分離

During a period from autumn 1992 to through summer 1993 in the North-Eastern Chiba Prefecture, appeared a syndrome characterized by respiratory disorders in 1-to 5-month old piglets, and anorexia and fever in sows with abortion, and delivery of stillborne, mummified, premature or weakborne piglets. From the affected pigs on 8 farms, viral agents were isolated on swine alveolar macrophage cultures and identified as porcine reproductive and respiratory syndrome (PRRS) virus. The antigenicity of the virus was closely related to that of the American PRRS virus. The retrospective antibody survey of the virus by indirect immunofluorescence revealed an epizootic in this area in 1988.

Laboratory investigation of PRRS virus infection in three swine herds.

Late in 1991, an enveloped RNA virus (now called porcine reproductive and respiratory syndrome [PRRS] virus) was identified as the etiologic agent for mystery swine disease. In 1992, laboratory procedures for the diagnosis of this disease evolved rapidly, and veterinary diagnosticians started applying these tests to field cases. This report is written from the perspective of veterinary laboratory diagnosticians and utilizes 3 case studies to define the advantages and disadvantages of the various available diagnostic laboratory PRRS test procedures in different clinical situations. The diagnostic procedures currently used in our laboratory for investigating PRRS are pathologic examination, serologic testing, fluorescent antibody (FA) testing, and virus isolation. Interstitial pneumonia, characterized by mononuclear cell infiltration of alveolar walls with normal airway epithelium, is a hallmark lesion for the disease, especially in neonatal pigs with respiratory distress. Interstitial pneumonia is not a specific lesion and must be coupled with other tests to verify PRRS virus infection. Demonstration of seroconversion is helpful, especially in sows that have experienced reproductive failure. The indirect FA test detects antibody sooner than the serum neutralization test and will likely become the serologic test of choice. The direct FA test on fresh tissue utilizes monoclonal antibody and is useful for investigating PRRS virus-associated pneumonia. Virus isolation utilizing swine alveolar macrophages has also been a useful diagnostic procedure. All of the above tests have been universally unrewarding when applied to aborted, mummified, or stillborn piglets.

Effects of pseudorabies virus infection upon cytotoxicity and antiviral activities of porcine alveolar macrophages

Alveolar macrophages (AM) infected with Pseudorabies virus (PRV) were compared to noninfected AM for cytotoxicity against foreign or transformed cells and production of interferon (IFN). Five PRV strains were used to infect AM including strains that are known to be highly virulent for pigs, i.e. strain 4892 and strain S-62 as well as strains that are regarded as mild or nonvirulent, i.e. BUK and Bartha. The multiplicity of infection ranged from 0.005 to 0.05 TCID 50/cell. The target cells in the cytotoxicity assays were either chicken red blood cells, PRV-infected vero cells, or human myeloblastoma cells (K562 cell line). For the producton of IFN, AM cultures were treated with polyinosinic: polycytidylic acid (Poly I:C) diluted in tissue culture media at a concentration of 5 μg/10 6 cells. Culture supernatants were collected at various times poststimulation and tested for antiviral activity using the Vesicular Stomatitis Virus replication inhibition test. Swine AM were able to lyse chicken red blood cells in an antibody-independent way but not in an antibody-dependent way, whereas lysis of PRV-infected vero cells was accomplished both ways. The cytotoxicity against chicken red blood cells was reduced in the PRV-infected AM as compared to noninfected cells, particularly in AM infected with virulent PRV strains. Specific 51Cr release values for AM infected with S-62 and 4892 strains were 14 and 19, while the noninfected AM had values of 36. Similarly, in the antibody-dependent cytotoxicity assay against PRV-infected vero cells there was no activity of AM against K562 cells. The production of IFN was readily stimulated with Poly I:C. The optimal time for supernatant collection was between 12 and 16h poststimulation. The antiviral activity was abrogated by treatment of the supernatant with antiserum against human leukocyte IFN; it was therefore considered to be due to interferon-alpha (IFNα) released from the macrophages. The antiviral activity present in supernatants of PRV-infected AM was reduced compared to noninfected AM. The difference between AM cultures infected with virulent strains of PRV and noninfected AM cultures was statistically significant at P ⩽ 0.025. The results provide support to the premise that the role of AM in lung defense can be compromised by PRV infection.

An indirect fluorescent antibody test for the detection of antibody to swine infertility and respiratory syndrome virus in swine sera.

An indirect fluorescent antibody (IFA) test was developed and standardized to detect and quantitate antibody for swine infertility and respiratory syndrome (SIRS) virus in swine sera. Test results were evaluated using sera of pigs infected both experimentally and naturally with SIRS virus. The IFA test used swine alveolar macrophage (SAM) monolayers prepared in 96-well microplates and infected with SIRS virus. The monolayers were incubated with test sera, washed, and stained with fluorescein isothiocyanate-labeled rabbit anti-swine IgG. After another wash step, the monolayers were examined under a fluorescent microscope. A noninfected SAM control well was included for each sample. The antibody titers for each serum sample were recorded as the highest serum dilutions with specific cytoplasmic fluorescence but no fluorescence in the control wells. To evaluate the test, sera of 4 6-week-old pigs that had been infected with SIRS virus, 2 contact pigs, and 13 experimentally infected sows were used. In the experimentally infected pigs, antibody was first detected at 7 days postexposure (PE) and peaked (1:256-1,024) between 11 and 21 days PE. All 13 sow sera were negative at time of infection but were positive (1:64- greater than or equal to 1:1,024) at 14-26 days PE. Seven hundred twenty sera collected from 25 different swine farms with or without a history of SIRS were also tested. Of 344 sera from 15 swine farms with a clinical history of SIRS, 257 (74.7%) sera had IFA titers greater than or equal to 1:4, whereas 371 (98.7%) of 376 sera from herds with no history of SIRS were negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of a cytopathic virus from weak pigs on farms with a history of swine infertility and respiratory syndrome.

Severe clinical signs of swine infertility and respiratory syndrome (SIRS) of unknown cause were observed in several Minnesota swine farms between November 1990 and March 1991. Forty-five lung samples of weak pigs were collected from 13 swine farms, and virus isolation was attempted using swine alveolar macrophage (SAM) cultures. A cytopathic virus was isolated from 19 lung samples collected from 6 different farms. Four pregnant sows were infected intranasally with a tissue suspension from which virus was isolated, and 4 6-week-old pigs and 2 contact pigs were infected intranasally with 1 of the isolates. The 4 sows farrowed 12 stillborn and 32 normal pigs. Virus was recovered from 10 of 19 pigs examined. Infected 6-week-old pigs were clinically normal except for slightly elevated rectal temperatures and mild respiratory signs. No or mild interstitial pneumonic lesions were observed in inoculated pigs, but the lesion was obvious in the 2 contact pigs. Seroconversion was observed in sows and pigs as measured by indirect fluorescent antibody (IFA). Serologic identification of the isolates was carried out by IFA using reference serum prepared from an experimentally infected sow. A cytoplasmic fluorescence was observed on the SAM monolayers infected with each of the 19 different isolates. Fluorescence was also observed when the monolayers were tested with SIRS virus ATCC VR-2332-infected sow sera. Replication of the isolates was not affected in the medium containing 5-iodo-2'-deoxyuridine but was inhibited by treatment with ether. The isolates were relatively stable at 56 C and did not agglutinate with various erythrocytes tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Activated porcine alveolar macrophages: Are biological response modifiers the answer?

We report that 75% of conventionally housed 3- to 4-week-old swine already have detectable activated alveolar macrophages as measured by cytotoxicity of tumor cells. These macrophages can not be further activated by the biological response modifier N-acetylmuramyl-L-alanyl-D-isoglutamine-2H 2O (MDP). These macrophages lose cytotoxic activity when cultured for 24 h and this loss of activity can not be reversed by MDP. We suggest that MDP biological response modifier therapy of swine alveolar macrophages may not be a useful technique in preventing respiratory disease in swine.

Interactions of pseudorabies virus with swine alveolar macrophages: effects of virus infection on cell functions.

In order to assess the effect of Pseudorabies virus (PRV) infection on the function of swine alveolar macrophages (AM), lung lavage cells were cultured, infected with one of six strains of PRV, and various activities were measured. Activity measurement included viability, phagocytosis of yeast, phagosome‐lysosome fusion, phagocytosis of opsonized particles, and superoxide release. AM were infected with 5 × 10‐3 PFU/cell, and the comparative assessment of functions was performed at 18‐20 h postinfection. Cell viability in PRV‐infected cultures ranged from 79 to 94% of the viability in noninfected cultures. Phagocytosis of yeast was significantly reduced only in the AM cultures infected with the strain S‐62. Phagosome‐lysosome fusion was depressed in cultures infected with the strains S‐62, 4892, 3816, and BUK. The phagocytosis of opsonized sheep red blood cells showed significant differences between noninfected and PRV‐infected cultures in all cases except cultures infected with the strain PRV‐C. The O2 release after stimulation with opsonized zymosan was significantly reduced in all the PRV‐infected cultures. The effect of PRV infection on AM functions that are related to the bacterial activity of such cells suggests that PRV‐induced AM dysfunction might have a role in the increased susceptibility of PRV‐infected pigs to bacterial pneumonia.

Interactions of Pseudorabies virus with swine alveolar macrophages I: virus replication

The replication of Pseudorabies virus (PRV) in cultured swine alveolar macrophages (AM) was studied using 6 different virus strains. AM were highly permissive to PRV infection, with progeny virus titres of 10(7) TCID50/ml from some strains. Virus progeny titres were higher in cultures infected with the field strains S-62 and 4892 than in cultures infected with the strains Bartha or PRV-C. Virus replication, viral DNA synthesis and the concomitant cell damage were dependent upon virus input m.o.i.s. and virus strain. Furthermore, cells from 7 day old pigs yielded higher virus progeny titres than cells of 6 week old pigs. The results from this study provide support to the premise that PRV infection may predispose anials to respiratory disease.

Effect of dihydroheptaprenol on nitroblue tetrazolium reduction by swine alveolar macrophages.

Effect of dihydroheptaprenol on nitroblue tetrazolium reduction by swine alveolar macrophages.