Recombinant Kluyveromyces lactis expressing highly pathogenic porcine reproductive and respiratory syndrome virus GP5 elicits mucosal and cell-mediated immune responses in mice

Currently, killed-virus and modified-live porcine reproductive and respiratory syndrome virus (PRRSV) vaccines are used to control porcine reproductive and respiratory syndrome. However, both types of vaccines have inherent drawbacks; accordingly, the development of novel PRRSV vaccines is urgently needed. Previous studies have suggested that yeast possesses adjuvant activities, and it has been used as an expression vehicle to elicit immune responses to foreign antigens. In this report, recombinant Kluyveromyces lactis expressing GP5 of HP-PRRSV (Yeast-GP5) was generated and immune responses to this construct were analyzed in mice. Intestinal mucosal PRRSV-specific sIgA antibody and higher levels of IFN-gamma in spleen CD4+ and CD8+ T cells were induced by oral administration of Yeast-GP5. Additionally, Yeast-GP5 administered subcutaneously evoked vigorous cell-mediated immunity, and PRRSV-specific lymphocyte proliferation and IFN-gamma secretion were detected in the splenocytes of mice. These results suggest that Yeast-GP5 has the potential for use as a vaccine for PRRSV in the future.

Positive effects of porcine IL-2 and IL-4 on virus-specific immune responses induced by the porcine reproductive and respiratory syndrome virus (PRRSV) ORF5 DNA vaccine in swine

The purpose of this study was to investigate the effects of porcine interleukin (IL)-2 and IL-4 genes on enhancing the immunogenicity of a porcine reproductive and respiratory syndrome virus ORF5 DNA vaccine in piglets. Eukaryotic expression plasmids pcDNA-ORF5, pcDNA-IL-2, and pcDNA-IL-4 were constructed and then expressed in Marc-145 cells. The effects of these genes were detected using an indirect immunofluorescent assay and reverse transcription polymerase chain reaction (RT-PCR). Characteristic fluorescence was observed at different times after pcDNA-ORF5 was expressed in the Marc-145 cells, and PCR products corresponding to ORF5, IL-2, and IL-4 genes were detected at 48 h. Based on these data, healthy piglets were injected intramuscularly with different combinations of the purified plasmids: pcDNA-ORF5 alone, pcDNA-ORF5 + pcDNA-IL-2, pcDNA-ORF5 + pcDNA-IL-4, and pcDNA-ORF5 + pcDNAIL-4 + pcDNA-IL-2. The ensuing humoral immune responses, percentages of CD4+ and CD8+ T lymphocytes, proliferation indices, and interferon-gamma expression were analyzed. Results revealed that the piglets co-immunized with pcDNA-ORF5 + pcDNA-IL-4 + pcDNA-IL-2 plasmids developed significantly higher antibody titers and neutralizing antibody levels, had significantly increased levels of specific T lymphocyte proliferation, elevated percentages of CD4+ and CD8+ T lymphocytes, and significantly higher IFN-gamma production than the other inoculated pigs (p < 0.05).

Seroprevalence of Antibody to Procine Reproductive and Respiratory Syndrome Virus in Diagnostic Submissions

During the period from January to December of 2001, a total of 3,391 swine sera were submitted to our laboratory from 256 farms for the diagnosis of porcine reproductive and respiratory syndrome (PRRS). The antibody to porcine reproductive and respiratory syndrome virus (PRRSV) was tested by the indirect immunofluorescent antibody (IFA) test. Of the 256 farms tested, 230 farms (89.8%) were positive for the PRRSV antibody. The overall seroprevalence of the PRRSV antibody was 52.1% (1765/3391). Most of the pigs seemed to be infected with PRRSV at around 50 to 60 days old. The seroprevalence of the antibody became higher with age, and peaked at around 100 days old. More than one-third of the adult pigs, including boars, gilts, and sows, was positive for the PRRSV antibody. The infection of PRRSV was chronic and confined to growers and/or finishers in most farms. However, the antibody was detected in all production phases at some farms.