Equine interferon-gamma and associated cytokines
Cytokines are small proteins or glycoproteins that mediate cellular growth and differentiation and regulate immune responses. Upon encounter with antigen, CD4+ T cells are able to influence the character of the immune response elicited through the expression of distinct types of cytokines. Thl cytokines, especially IFN-γ but also TNF-β and IL-2, constitute one such pattern of expression, promoting cell mediated immune responses. In a broader sense, interleukin-12 and interleukin-18 can also be classified as type I cytokines in as much as they are able to shift the CD4+ cytokine expression pattern to a Thl phenotype and specifically stimulate IFN-γ production not only by T helper cells, but also by cytotoxic T cells and natural killer cells. The purpose of the present project was to develop equine Thl cytokines, making them available for dissecting the equine immune system, particularly in what concerns to defence mechanisms against infectious micro-organisms. Following the trend in human medicine, the cytokines produced will be useful for the development of new therapeuticals and prophylactics to be used in the control and prevention of infectious diseases of the horse. For this effect we have initiated studies on equine interferon-gamma and related cytokines and obtained the following results. Equine interferon-gamma was cloned and produced in a variety of heterologous protein-expression systems. The biological activity of recombinant equine interferon-gamma was assessed in vitro. Polyclonal serum preparations against equine interferon-gamma, obtained by immunization with recombinant protein, were recovered and characterised. Also described is the cloning of the interferon-gamma inducing cytokines equine interleukin-12 and equine interleukin-18. The potential use of the cloned equine cytokine genes as vaccine adjuvants was evaluated by DNA co-administration with plasmids encoding the equine influenza virus antigens haemagglutinin and nucleoprotein, followed by viral challenge.