OBJECTIVE: IBD is characterised by dysregulated intestinal immune homeostasis 
and cytokine secretion. In the intestine, properly regulating pattern 
recognition receptor (PRR)-mediated signalling and cytokines is crucial given 
the ongoing host-microbial interactions. TPL2 (MAP3K8, COT) contributes to 
PRR-initiated pathways, yet the mechanisms for TPL2 signalling contributions in 
primary human myeloid cells are incompletely understood and its role in 
intestinal myeloid cells is poorly defined. Furthermore, functional consequences 
for the IBD-risk locus rs1042058 in TPL2 are unknown.
METHODS: We analysed protein, cytokine and RNA expression, and signalling in 
human monocyte-derived macrophages (MDMs) through western blot, ELISA, real-time 
PCR and flow cytometry.
RESULTS: PRR-induced cytokine secretion was increased in MDMs from rs1042058 
TPL2 GG risk individuals. TPL2 activation by the Crohn's disease-associated PRR 
nucleotide-oligomerisation domain (NOD)2 required PKC, and IKKβ, IKKα and IKKγ 
signalling. TPL2, in turn, significantly enhanced NOD2-induced ERK, JNK and NFκB 
signalling. We found that another major mechanism for the TPL2 contribution to 
NOD2 signalling was through ERK-dependent and JNK-dependent caspase-1 and 
caspase-8 activation, which in turn, led to early autocrine interleukin (IL)-1β 
and IL-18 secretion and amplification of long-term cytokines. Importantly, 
Salmonella typhimurium-induced cytokines from human intestinal myeloid-derived 
cells required TPL2 as well as autocrine IL-1β and IL-18. Finally, rs1042058 GG 
risk carrier MDMs from healthy individuals and patients with Crohn's disease had 
increased TPL2 expression and NOD2-initiated TPL2 phosphorylation, ERK, JNK and 
NFκB activation, and early autocrine IL-1β and IL-18 secretion.
CONCLUSIONS: Taken together, the rs1042058 GG IBD-risk polymorphism in TPL2 
results in a gain-of-function by increasing TPL2 expression and signalling, 
thereby amplifying PRR-initiated outcomes.