|M.Sc Thesis||Department of Medicine|
|Supervisor:||Assoc. Prof. Pollack Shimon|
|Full Thesis text - in Hebrew|
Circulating monocytes and tissue macrophages have an essential role in the innate and adaptive immune responses. When stimulated, they release a whole array of cytokines like IL-1, IL-6, IL-8, IL-10, IL-12, IL-15, and can also be induced by IL-16 to secrete various chemokines.
IL-15 is a pro-inflammatory cytokine which mimics IL-2 functions. Two of its receptor subunits (β and γC) are in common with the IL-2 receptor .The α subunit is unique for IL-15R or IL-2R and binds IL-15 or IL-2, respectively, with high affinity.
IL-16 is a pro-inflammatory chemoattractant cytokine. IL-16 induces the expression of IL-2Rα in T-cells and monocytic cells.
Our working hypothesis was that because of the functional similarities between IL-2 and IL-15 on the one hand and the structural similarities between IL-2R and IL-15R on the other hand, IL-16 may induce, in addition to IL-2Rα, also IL-15Rα expression on monocytic cells. This, in turn, may enable an interaction between IL-15 and IL-16 that will result in the activation of various signaling pathways that mediate this interaction and culminate in cytokine/chemokine secretion.
As a source of human monocytes we used the human monocytic cell line THP-1 cells, either differentiated (PMA-Mac) or naïve and also Human (peripheral blood) Monocyte-Derived Macrophages (HMDM). IL-15 was extracted from cDNA of THP-1 cells. The expression of IL-15Rα was detected by Western Immunoblotting and signal transduction pathways in monocytic cells were analyzed by the same method. Secretion of cytokines and chemokines was screened by Cytokine Array and quantitated by ELISA.
Our main findings are that IL-16 had no effect on IL-15Rα expression .Co-stimulation with IL-15 and IL-16 caused an increase in ERK1/2 phosphorylation in PMA-Mac. We could not show any phosphorylation changes in the Src- tyrosine kinases and JAK-STAT pathways. By using Cytokine Array we could demonstrate a significant increase in monocyte secretion of IL-8, in addition to RANTES and MCP-1, after co-stimulation with IL-15 and IL-16.
In conclusion, our findings suggest an interaction between IL-15 and IL-16 in stimulation of differentiated monocytes (PMA-Mac) which leads to increased ERK1/2 tyrosine phosphorylaion. The synergistic effect of co-stimulation with IL-15 and IL-16 on the increase in ERK enzymes phosphorylation may be responsible for the significant increased secretion of IL-8 in addition to RANTES and MCP-1 in the co-stimulated cells. The demonstrated interaction between IL-15 and IL-16 may be relevant for the pathological consequences of an inflammatory response which accompanies infection.