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-alpha, IL-1alpha, 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-alpha 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.

Expression and purification of recombinant swine interleukin-4

The swine interleukin-4 (SwIL-4) cDNA was cloned by RT-PCR. It was expressed using an expression vector pQE30 in E. coli, a baculovirus AcNPV vector pVL1392 in insect cells, and a pCAGGS vector in mammalian cells. The rSwIL-4 proteins expressed from bacteria and insect cells were purified using a chelating affinity column and a mAb-coupled immunoaffinity column. The amount of the products and their bioactivities were compared. All recombinant cytokines were efficiently reacted with the specific antibodies and the molecular weight of rSwIL-4 was approximately 16 kDa in E. coli, 15 and 18 kDa in insect cells, and 15 and 20 kDa in mammalian cells. Variations of molecular weight observed in insect and mammalian cells were probably due to different modification ways of glycosylation. All these recombinant proteins retained their antigenicity and were biologically active in inducing human TF-1 cell proliferation in vitro. The simple purification method will make it possible to evaluate the in vitro and in vivo effects of IL-4 in pigs.

Expression and characterization of the recombinant swine interleukin-6

The swine interleukin-6 (SwIL-6) cDNA was cloned by RT-PCR and each expression system of recombinant SwIL-6 in Escherichia coli, insect cells, and mammalian cells was developed. Recombinant SwIL-6 produced in bacteria was applied for generation of the polyclonal antibodies. The rSwIL-6 was purified from supernatant of insect cells with a Q-sepharose or anti-SwIL-6 monoclonal antibody based immunoaffinity column. The antibodies showed that the molecular weight of rSwIL-6 was approximately 26kDa in E. coli, 25, 26, 30kDa in insect cells, and 26 and 30kDa in mammalian cells. These variations of molecular weight were probably due to the different modifications of glycosylation. All these recombinant proteins retained the antigenicity and biological activity on 7TD1 mouse cells.

Establishment of swine interleukin-6 sandwich ELISA

We established a sandwich enzyme-linked immunosorbent assay (ELISA) for swine interleukin-6 (SwIL-6), which was applied for detection of SwIL-6 in vitro and in vivo. Anti-SwIL-6 rabbit- and goat-polyclonal antibodies, and monoclonal antibody (mAb) were prepared, conforming that all of the antibodies were reactive with recombinant SwIL-6 by Western blotting and indirect ELISA. A sandwich ELISA was developed using the mAb as a capture antibody and biotinylated goat-polyclonal antibody as a detection antibody. The detection limit of the sandwich ELISA for rSwIL-6 was 49pg/ml and did not show cross-reactivity with swine IL-1b, IL-4, IL-8, IL-18, IL-12, and IFN-g. Using the ELISA, SwIL-6 was detected in culture medium of the monocytes stimulated with PHA-P and PMA, and the plasma or the bronchoalveolar lavage fluid (BALF) of pigs experimentally infected with Actinobacillus pleuropneumoniae or Mycoplasma hyopneumoniae. This ELISA for SwIL-6 may be useful for understanding the role of this cytokine in various swine diseases.

Characterization of specific antibodies and the establishment of sandwich ELISA and ELISPOT systems for swine IL-4

We produced four monoclonal antibodies (mAb) and two polyclonal antibodies using the purified cytokine expressed in bacteria and characterized them. Specific binding of each of the mAb and polyclonal antibodies to recombinant swine IL-4 (rSwIL-4) purified from Escherichia coli and baculovirus was demonstrated in an indirect ELISA and/or in western blotting. We established a sandwich enzyme-linked immunosorbent assay (ELISA) for measuring concentration of SwIL-4 in biological samples and established an enzyme-linked immunospot (ELISPOT) assay for detecting IL-4-secreting cells using a mAb and a polyclonal IgG from goat. The detection limit of the sandwich ELISA for SwIL-4 was 78 pg/ml. Using sandwich ELISA, SwIL-4 was detected in the bronchoalveolar lavage fluid (BALF) of pigs experimentally infected with Mycoplasma hyopneumoniae and could quantitate in supernatants of mitogen-stimulated PBMC culture. The ELISPOT system is useful for the detection of IL-4 producing cells in swine PBMC culture.

Rinderpest virus H protein: role in determining host range in rabbits

A major molecular determinant of virus host-range is thought to be the viral protein required for cell attachment. We used a recombinant strain of Rinderpest virus (RPV) to examine the role of this protein in determining the ability of RPV to replicate in rabbits. The recombinant was based on the RBOK vaccine strain, which is avirulent in rabbits, carrying the haemagglutinin (H) protein gene from the lapinized RPV (RPV-L) strain, which is pathogenic in rabbits. The recombinant virus (rRPV-lapH) was rescued from a cDNA of the RBOK strain in which the H gene was replaced with that from the RPV-L strain. The recombinant grew at a rate equivalent to the RPV-RBOK parental virus in B95a cells but at a lower rate than RPV-L. The H gene swap did not affect the ability of the RBOK virus to act as a vaccine to protect cattle against virulent RPV challenge. Rabbits inoculated with RPV-L became feverish, showed a decrease in body weight gain and leukopenia. High virus titres and histopathological lesions in the lymphoid tissues were also observed. Clinical signs of infection were never observed in rabbits inoculated with either RPV-RBOK or with rRPV-lapH; however, unlike RPV-RBOK, both RPV-L and rRPV-lapH induced a marked antibody response in rabbits. Therefore, the H protein plays an important role in allowing infection to occur in rabbits but other viral proteins are clearly required for full RPV pathogenicity to be manifest in this species.