Recombinant canine IL-13 receptor alpha2-Fc fusion protein inhibits canine allergen-specific-IgE production in vitro by peripheral blood mononuclear cells from allergic dogs.

Human IL-13, like IL-4, is involved in the regulation of B-cell development, IgE synthesis and allergic responses. However, because IL-13 does not affect either murine Ig class switching or IgE production in vitro, the use of murine models to study the role of IL-13 in IgE-mediated diseases has been limited. In this communication, we report that recombinant protein of canine IL-13 (rcaIL-13) stimulates production of allergen-specific-IgE in vitro by peripheral blood mononuclear cells (PBMC) from flea allergen-sensitized dogs, and that this stimulation activity is specifically inhibited by recombinant protein of canine IL-13Ralpha2 and Fc fragment of canine IgG heavy chain (rcaIL-13Ralpha2-Fc). The data suggest that the regulatory effects of IL-13 on IgE production in canine PBMC are similar to those reported in humans. Thus, canine IL-13 may be a central mediator of allergic diseases in dogs, and allergic dogs may be excellent models for research on IgE-mediated diseases in humans.

Canine interleukin-13: molecular cloning of full-length cDNA and expression of biologically active recombinant protein.

Interleukin-13 (IL-13) regulates immune responses mediated by type 2 T helper lymphocytes (Th2) in the human and mouse. To study the function of this cytokine in the dog, we have isolated a cDNA that encodes the full-length canine IL-13 (CaIL-13) precursor polypeptide of 131 amino acids. CaIL-13 shares significant homology with the IL-13 amino acid sequences of cattle (54.1%), mouse (39.6%), and rat (36.6%) but shares the highest identity with human IL-13 (HuIL-13) (61.8%). The predicted CaIL-13 mature polypeptide of 111 residues was expressed in bacteria, and recombinant CaIL-13 (rCaIL-13) was isolated from inclusion bodies and refolded. rCaIL-13 stimulated the proliferation of TF-1 cells, which are derived from human erythroleukemia cells and respond to IL-13 as well as to a number of other human and murine cytokines. CaIL-13 mRNA was readily detectable by reverse transcriptase-polymerase chain reaction (RT-PCR) in cells from lymph nodes and peripheral blood. The gene sequence and biologically active recombinant protein for CaIL-13 will be useful reagents to determine the role of IL-13 in the regulation of canine immune responses.

Multifaceted inhibition of anti-tumour immune mechanisms by soluble tumour necrosis factor receptor type I.

Soluble tumour necrosis factor receptor type I (sTNFRI) is a potent inhibitor of TNF with the potential to suppress a variety of effector mechanisms important in tumour immunity. That sTNFRI influences tumour survival in vivo is suggested by results from human clinical trials of Ultrapheresis, an experimental extracorporeal treatment for cancer. While the considerable clinical benefit provided by Ultrapheresis is correlated with the removal of plasma sTNFRI, there is no direct evidence that sTNFRI inhibits immune mechanisms which mediate tumour cell elimination. To evaluate formally the ability of sTNFRI to inhibit these mechanisms, we have engineered sTNFRI production into the TNF-sensitive murine fibrosarcoma cell line, L929. Soluble TNFRI-secreting L929 cells display increased resistance to direct lysis by TNF, and to lysis by syngeneic lymphokine-activated killer cells and cytotoxic T cells. These findings confirm the suggestion that sTNFRI inhibits immunological mechanisms important in tumour cell eradication, and further support a role for sTNFRI in tumour survival in vivo. In addition, these observations suggest the development of methods for more specific removal and/or inactivation of sTNFRI as promising new avenues for cancer immunotherapy.

Pathogenic potential of myeloblastosis-associated virus: implication of env proteins for osteopetrosis induction.

To identify the nucleotide sequences responsible for the tumorigenic specificity of myeloblastosis-associated virus (MAV) we have established the complete nucleotide sequences of three infectious clones inducing either both osteopetrosis and nephroblastoma [MAV2(O)/2 and MAV2(O)p9] or only nephroblastoma [MAV1(N)], and compared their biological properties in the same chicken host strain. The MAV2(O)p9 originally described as a type 2 strain was found to carry a hybrid env gene containing sequences of both the types 1 and 2, and it induced milder and less rapid osteopetrosis than the original MAV2(O) clone when injected into Brown Leghorn chickens. These results, together with sequence comparisons between the MAV strains examined, suggest that subtle changes in the primary structure of the TM env protein's extracellular domain are likely to affect the tumorigenic potential of MAV.