Cloning, expression and biological activity of equine interleukin (IL)-5

Role of intracellular kinases in the regulation of equine eosinophil migration and actin polymerization

Inappropriately activated eosinophils can contribute to disease pathogenesis and intracellular signalling pathways that regulate functional responses may represent a therapeutic target. Little is known about intracellular signalling in equine eosinophils and this study examined the role of phospholipase C (PLC) and a range of protein kinases on responses to histamine and CCL11. Histamine (10(-4) M) or CCL11 (5.6 x 10(-9) M)-induced actin polymerization, migration and superoxide production by eosinophils from healthy horses were compared in the presence and absence of selective kinase inhibitors. Inhibition of phosphatidylinositol-3 kinase (PI3K) significantly reduced the response in each assay. In contrast, whilst inhibition of PLC decreased actin polymerization and superoxide production, an increase in migration was observed; the latter effect was also seen when protein kinase C (PKC) was inhibited. With the exception of histamine-induced migration, which was significantly reduced by blocking extracellular regulated kinase (ERK)1/2, activation of ERK1/2, p38 MAPK and tyrosine kinase did not appear to play an important role in the responses studied. These results suggest that equine eosinophil activation by histamine and CCL11 is mediated through PI3K. Whilst PLC activation is required for actin polymerization and superoxide production, migration may be negatively regulated by PLC and PKC. These kinases represent potential targets for modulating eosinophil activation by multiple stimuli.

Equine recurrent airway obstruction and insect bite hypersensitivity: understanding the diseases and uncovering possible new therapeutic approaches

Recurrent airway obstruction (RAO) and insect bite hypersensitivity (IBH) are allergic conditions that are commonly encountered in the horse. Whilst complete allergen avoidance is an effective management strategy for both diseases, this may not be achievable in all cases and treatment options are therefore required. The inflammatory response is the main therapeutic target for glucocorticoids given to horses with RAO and severe cases of IBH, whilst the bronchodilators used in RAO primarily target airway smooth muscle. Such drugs are effective in most but not all individuals and there may be unwanted adverse effects. This article will review how knowledge of drug action and the pathogenesis of RAO and IBH can be utilised to identify potential targets for novel therapeutic agents that, in the longer term, may be safer and/or more effective in managing the allergic horse.

Horse cytokine/IgG fusion proteins – mammalian expression of biologically active cytokines and a system to verify antibody specificity to equine cytokines

Recombinant cytokines are valuable tools for functional studies and candidates for vaccine additives or therapeutic use in various diseases. They can also be used to generate specific antibodies to analyze the roles of different cytokines during immune responses. We generated a mammalian expression system for recombinant cytokines using the equine IgG1 heavy chain constant region as a tag for detection and purification of the expressed cytokine, demonstrated here using equine interferon-gamma (IFN-gamma), interleukin-2 (IL-2), interleukin-4 (IL4) and transforming growth factor-beta1 (TGF-beta1). The resulting IgG1 fusion proteins were composed of the C-terminal heavy chain constant region of the IgG1 (IgGa), and the N-terminal cytokine replacing the immunoglobulin heavy chain variable domain. The fusion proteins were expressed in CHO cells as dimers and their structures had similarity to that of IgG heavy chain antibodies. In contrast to other tags, the IgG1 heavy chain constant region allowed the selection for clones secreting high levels of the recombinant protein by a sensitive ELISA. In addition, the IgG1 heavy chain constant region facilitated identification of stable transfectants by flow cytometry and the secreted recombinant fusion protein by SDS-PAGE and Western blotting. To recover the cytokine from the IgG1 fusion partner, an enterokinase cleavage site was cloned between the cytokine gene and the immunoglobulin heavy chain constant region gene. The purification of the fusion protein by protein G affinity columns, the enterokinase digestion of the cytokine from the IgG1 heavy chain region after or during purification, and the biological activity of the cytokine within the fusion protein or after its isolation was demonstrated in detail for equine IFN-gamma/IgG1 by up-regulation of major histocompatibility complex (MHC) class II expression on horse lymphocytes. Biological activity could also be confirmed for the IL-2 and IL-4/IgG1 fusion proteins. To test the crossreactivity and specificity of anti-human TGF-beta1, and anti-bovine and anti-canine IFN-gamma antibodies to respective horse cytokines, the four cytokine/IgG1 fusion proteins were successfully used in ELISA, flow cytometry and/or Western blotting. In summary, equine IgG1 fusion proteins provide a source of recombinant proteins with high structural and functional homology to their native counterparts, including a convenient system for selection of stable, high expressing transfectants, and a means for monitoring specificity of antibodies to equine cytokines.