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. Author manuscript; available in PMC: 2014 Apr 7.
Published in final edited form as: Immunol Rev. 2009 Sep;231(1):265–277. doi: 10.1111/j.1600-065X.2009.00822.x

Figure 3. Scavenger receptor mediated calcium signaling in B cells.

Figure 3

Unmethylated CpG DNA triggers a robust calcium signal in primary B cells via the Scavenger Receptor-B1. The mechanism of CpG induced calcium entry is distinct from that elicited by the BCR and by mechanical stimulation in several critical respects. First, PLCγ-1 and not PLCγ-2 is required for SR-B1 mediate calcium mobilization. Second, SR-B1 mediated calcium entry occurs via TRPC3 channels. Finally, although CpG activation SR-B1 triggers calcium release from stores, TRPC3 activation is store independent and; furthermore, PLCγ-1 appears to activate TRPC3 via a direct physical interactions between these two proteins and is not regulated by calcium release from stores. Interestingly, CpG does not activate CRAC channels in spite of its ability to trigger calcium release from ER. This suppression of CRAC channel mediated calcium entry could reflect (1) inhibition of calcium permeation of CRAC channels by TRPC3 mediated membrane depolarization, (2) insufficient IP3 production or depletion of calcium from stores to mobilize STIM1, or (3) sufficient calcium depletion and STIM1 mobilization but an inability to activate Syk, Lyn, or SLP-65 as required for positive regulation of distal coupling between stores and CRAC channels (see text).