The host immune response to parasitic helminths is usually characterized by a Th2 phenotype. As the Jagged/Notch pathway has been implicated in driving Th2 development, it was hypothesized that host macrophages and dendritic cells (DCs) could detect helminth products and mount an appropriate response via this pathway. Schistosoma mansoni soluble egg antigen (SEA) rapidly up-regulated expression of the Notch ligand, Jagged 1, in both mouse and human macrophages, as well as in conventional mouse DCs. Other factors associated with Th cell development, including the Th1-promoting factor IL-12 p40, as well as another potential Th2-promoting factor, interleukin (IL)-33, were not transcriptionally responsive to SEA in these same cell types, thus indicating the selectivity of the response. Inducible gene expression was modified by the presence of the macrophage growth factor colony-stimulating factor (CSF)-1, which inhibited Jagged 1 induction by SEA and lipopolysaccharide (LPS), but enhanced LPS-induced IL-12p40 expression. Despite the observation that SEA upregulated Jagged 1 in both macrophages and DCs, only SEA-pulsed DCs promoted IL-4 production upon T-cell activation, suggesting that Jagged 1 induction alone is insufficient for instructing Th2 development. A recombinant form of the extracellular region of Jagged 1 did, however, enhance IFN-γ production in splenocytes, thus implying that the rapid induction of Jagged 1 in macrophages and DCs can regulate T cell responses. A potential role for SEA-induced Jagged 1 in autocrine responses in macrophages was also investigated through studies with recombinant extracellular Jagged 1, as well as ectopic expression of Jagged 1 in macrophages. A comparison of the responses initiated in macrophages by SEA and the bacterial endotoxin lipopolysaccharide (LPS) revealed common activation of extracellular signal regulated kinase-1/2 (ERK-1/2) and p38 phosphorylation. However, only LPS triggered IκB degradation, phosphorylation of c-Jun N-terminal kinase (JNK) and phosphorylation of Tyr701 of signal transducer and activator of transcription 1 (STAT1). SEA robustly activated signalling in HEK293 cells expressing either Toll-like receptor 2 (TLR2) or TLR4/MD2, as well as variably in cells expressing TLR3. Jagged 1 upregulation by SEA was not abrogated in TLR4 knockout macrophages, in contrast to the LPS response. Pharmacological inhibition of the ERK-1/2 pathway impaired both SEA- and LPS-inducible Jagged 1 expression in macrophages. In conclusion, the data within this thesis suggests that Jagged 1 is an ERK-dependent target of TLR signalling that has a macrophage-specific function in the response to SEA.

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