Characterisation of the porcine cytokines which activate the CD131ßc common sub-unit, for potential immune-augmentation.

Early acting cytokines and growth factors such as those of the CD131 ßc subunit, may offer an alternative method to the current use of antibiotics and chemicals such as anthelmintics in maintaining Porcine (Po) health. Thus far, the recombinant Po (rPo) Granulocyte-macrophage colony-stimulating factor (GM-CSF), rPo interleukin-3 (IL-3) and rPo interleukin-5 (IL-5) proteins have been identified and cloned and the biological activity of each cytokine has been confirmed in vitro, however, in vivo immune system regulation and hematopoietic stem cell (HSC) augmentation are regulated by numerous cytokines and cellular signals within the bone marrow (BM) niche. In order to quantify the use of recombinant cytokines in augmenting the immune response, it is necessary to determine the stages of hematopoiesis induced by each cytokine and possible areas of synergy requiring further investigation. Here we used the chemotherapeutic agent 5-fluorouracil (5-FU), to chemically induce a state of myelosuppression in young pigs. This allowed for the monitoring of both the autologous BM reconstitution and recombinant cytokine induced BM repopulation, precursor cell proliferation and cellular differentiation. The recombinant cytokines PoGM-CSF, PoIL-3 and PoIL-5 were administered by intramuscular injections (i.m.) following confirmation of 5-FU induced leukocytopenia. Blood and BM samples were collected and then analysed for cell composition. Statistically significant results were observed in several blood cell populations including eosinophils for animals treated with rPoIL-5, rPoGM-CSF and basophils for animals treated with rPoIL-3. BM analysis of CD90+ and CD172a+ cells confirmed myelosuppression in week one with significant results observed between rPoIL-3 and the 5-FU control group in week two and for the rPoGM-CSF group in week three. These results have demonstrated the effects of each of these rPo cytokines within the hematopoietic processes of the pig and may demonstrate similar outcomes in other mammalian models including human.

The Ig-like domain of human GM-CSF receptor alpha plays a critical role in cytokine binding and receptor activation.

GM-CSF (granulocyte/macrophage colony-stimulating factor) is an important mediator of inducible haemopoiesis and inflammation, and has a critical role in the function of alveolar macrophages. Its clinical applications include the mobilization of haemopoietic progenitors, and a role as an immune stimulant and vaccine adjuvant in cancer patients. GM-CSF signals via a specific alpha receptor (GM-CSFRalpha) and the shared hbetac (human common beta-subunit). The present study has investigated the role of the Ig-like domain of GM-CSFRalpha in GM-CSF binding and signalling. Deletion of the Ig-like domain abolished direct GM-CSF binding and decreased growth signalling in the presence of hbetac. To locate the specific residues in the Ig-like domain of GM-CSFRalpha involved in GM-CSF binding, a structural alignment was made with a related receptor, IL-13Ralpha1 (interleukin-13 receptor alpha1), whose structure and mode of interaction with its ligand has recently been elucidated. Mutagenesis of candidate residues in the predicted region of interaction identified Val51 and Cys60 as having critical roles in binding to the alpha receptor, with Arg54 and Leu55 also being important. High-affinity binding in the presence of hbetac was strongly affected by mutation of Cys60 and was also reduced by mutation of Val51, Arg54 and Leu55. Of the four key residues, growth signalling was most severely affected by mutation of Cys60. The results indicate a previously unrecognized role for the Ig-like domain, and in particular Cys60, of GM-CSFRalpha in the binding of GM-CSF and subsequent activation of cellular signalling.