Gliding bacterial adjuvant stimulates feline cytokines in vitro and antigen-specific IgG in vivo.

Gliding bacterial adjuvant (GBA) has been previously characterized as a potent immune modulator, stimulating the growth of murine B lymphocytes, inducing murine NK cell activity, and promoting the release of several murine cytokines. Based on these studies and our interest in potentiating the effectiveness of feline vaccines, GBA was tested for its ability to stimulate feline T cells in vitro and act as a vaccine adjuvant in vivo. In vitro, GBA stimulated feline PBLs to proliferate and release interferon (IFN) and IL-2. Unlike IFN, the release of IL-2 appeared to be unaffected by prior depletion of macrophages, indicating GBA directly stimulated feline T cells. In vivo GBA was co-administered with Keyhole Limpet Hemacyanin (KLH) and the anti-KLH antibody response was compared to cats receiving KLH emulsified in complete Freund's adjuvant (CFA). Fourteen days after the third immunization and continuing for a 30-day observation period, KLH-specific IgG titers in cats receiving GBA were significantly higher than those given CFA. However, when cats were subsequently boosted with KLH alone, those cats receiving CFA demonstrated significantly higher antibody titers throughout a second 30-day observation period. The anti-KLH antibody memory response was greatly enhanced when GBA was emulsified with incomplete Freunds adjuvant (IFA) prior to injection. Serum titers of cats given KLH in an oil-based GBA preparation were significantly higher than cats receiving KLH adjuvanted with IFA or CFA, an effect which persisted 38 days after boosting with KLH alone. Finally, GBA significantly enhanced the feline humoral response to a recombinant protein of Dirofilaria immitis, the causative agent of feline heartworm. Serum titers of cats inoculated with recombinant antigen in GBA were significantly greater than cats given recombinant antigen adjuvanted with Titermax, alum, or NAGO. These studies indicate that GBA induces T cell proliferation and the release of IL-2 and IFN in vitro and can be used to enhance the recall antibody response to both a T cell dependent antigen and an immunogen derived from Dirofilaria immitis.