Vaccine adjuvants containing analogs of microbial products activate
pattern recognition receptors (
PRRs) on antigen-presenting cells, including monocytes and macrophages, which can cause
prostaglandin E2 (
PGE2) release and consequently undesired inflammatory responses and
fever in
vaccine recipients. Here, we studied the mechanism of
PGE2 production by human monocytes activated with
muramyl dipeptide (MDP) adjuvant, which activates cytosolic
nucleotide-binding oligomerization domain 2 (NOD2). In rabbits, administration of MDP elicited an early increase in
PGE2 followed by
fever. In human monocytes, MDP alone did not induce
PGE2 production. However, high amounts of
PGE2 and the proinflammatory
cytokines IL-1β and
IL-6 were secreted by monocytes activated with MDP in the presence of
conditioned medium obtained from CD3 bead-isolated T cells (Tc CM) but not from those isolated without CD3 beads. Mass spectrometry and immunoblotting revealed that the costimulatory factor in Tc CM was
glycoprotein Ib α (GPIbα). Antibody-mediated blockade of GPIbα or of its receptor, Mac-1
integrin, inhibited the secretion of
PGE2, IL-1β, and
IL-6 in MDP + Tc CM-activated monocytes, whereas recombinant GPIbα
protein increased
PGE2 production by MDP-treated monocytes. In vivo, COX2
mRNA abundance was reduced in the liver and spleen of Mac-1 KO mice after administration of MDP compared with that of treated wild-type mice. Our findings suggest that the production of
PGE2 and proinflammatory
cytokines by MDP-activated monocytes is mediated by cooperation between two signaling pathways: one delivered by MDP through NOD2 and a second through activation of Mac-1 by T cell-derived GPIbα.