Characterization of swine infertility and respiratory syndrome (SIRS) virus (isolate ATCC VR-2332).

The characterization of an isolate of swine infertility and respiratory syndrome (SIRS) virus (ATCC VR-2332) is reported. A commercial cell line (CL2621) was used for the propagation of the virus for all assays. Laboratory studies indicate that this isolate is a fastidious, nonhemagglutinating, enveloped RNA virus. Cesium chloride-purified virions visualized by electron microscopy were spherical particles with an average diameter of 62 nm (range: 48-83 nm) and a 25-30 nm core surrounded by an envelope. Virus replication was restricted to the cytoplasm, as demonstrated by immunofluorescence. The virus did not react serologically with antisera to several common porcine viruses or with antisera to known viruses in the alphavirus, rubivirus, pestivirus, and ungrouped lactic dehydrogenase virus genera of the Togaviridae. However, convalescent sow sera and rabbit hyperimmune sera neutralized the SIRS virus at titers of 1:256 and 1:512, respectively. The virus was stable at 4 and -70 C, but was labile at 37 and 56 C. The properties of this isolate of SIRS virus resemble those of the family Togaviridae but do not match the described genera.

Experimental reproduction of swine infertility and respiratory syndrome in pregnant sows.

The purpose of this study was to experimentally reproduce swine infertility and respiratory syndrome (SIRS). Six multiparous sows were intranasally inoculated at 93 days of gestation with lung homogenates from clinically affected pigs, and 3 additional sows were similarly inoculated with a virus isolated in cell culture from the lung homogenate (SIRS virus, isolate ATCC VR-2332). Inoculated sows developed transient anorexia, farrowed up to 7 days prematurely, and delivered a mean of 5.8 live pigs and 6.0 dead fetuses/litter. Clinical signs of disease were not observed in 3 sham-inoculated control sows that delivered a mean of 12.7 live pigs and 0.3 stillborn fetuses/litter. The SIRS virus was isolated from 50 of 76 live-born and stillborn fetuses from the 9 infected litters. Virus was not isolated from 26 autolyzed fetuses or 15 control pigs. Six of 9 inoculated sows developed neutralizing antibodies to SIRS virus. The reproductive effects found in these experiments were identical to those found in field cases. On the basis of our findings, virus isolate ATCC VR-2332 causes the reproductive failure associated with SIRS.

The immune response of allophenic mice to the synthetic polymer GL phi. III. Allotype analysis of anti-GL phi antibody.

Allophenic mice produced by aggregating 8-cell embryos from a low responder (CBA) and a high responder (DBA/1) strain to the synthetic amino acid polymer GL phi.. In some strains of mice the immune response to this polymer is controlled by two genes, alpha and beta, which map to the IE/C and IA subregions of the H-2 complex, respectively. The CBA strain is alpha+beta--whereas the DBA/1 strain can be considered to be alpha+beta+. These two strains also differ in immunoglobulin allotype: CBA is allotype alpha and DBA/1 is allotype c. Eight CBA--DBA/1 allophenic mice were immunized with GL phi.. Four of the mice gave a high secondary response to the polymer. The allotype of the antibody from these mice was determined by affinity chromatography, and it was found that only allotype c was present. This means that all of the antibody was produced by high responder DBA/1 cells. Thus, there is no evidence for the cooperation of histoincompatible cells in the mounting of an immune response by allophenic mice.