Simplified scheme of RBL-2H3 cells' degranulation pathways.
The DNP antigen activates multiple signal transduction pathways via the IgE anti-DNP/FcεRI receptor complex. DNP receptor binding activates the immunoreceptor tyrosine activation motifs (ITAM)-Spleen tyrosine kinase (SyK) pathway that can be inhibited by shikonin [35] and probably by naphthazarin. Activated Syk catalyses protein phosphorylation of several proteins, leading indirectly to the activation of protein kinase C (PKC) that induces degranulation and the activation of phospholipase A2 (PLA2). PLA2 increases arachidonic acid (AA) bioavailability that can be converted in leukotrienes (LT) by 5-lipoxygenase (5LO; inhibited by menadione), or in oxidized lipids by means of ROS production. 5LO converts AA into 5-hydroperoxyeicosatetraenoic acid (5-HPETE), which is metabolised to an unstable epoxide, LTA4, and finally in LTC4, in RBL-2H3 cells. The increase in intracellular calcium by SyK pathway, as well as by A23187 promotes degranulation.
