FIGURE 4.

Role of scavenger receptor B1 in CpG-mediated calcium signaling. A, CpG-induced Ca²⁺ signals are blocked by the non-selective scavenger receptor ligands poly-inosine (Poly I), fucoidan, and low density lipoprotein (LDL). B, reverse transcription-PCR analysis demonstrates expression of CD36, MARCO, and splice variants SR-B1 and SR-B2 in primary B lymphocytes. RNA isolated from macrophages served as a positive control for SREC-I, SREC-II, macrosialin, and SR-A1 primers. C, anti-SR-B1 antibody partially blocks CpG-induced Ca²⁺ signals. D, SR-B1 expression is required for CpG- but not BCR-induced Ca²⁺ signaling. BCR engagement produces similar Ca²⁺ signals in SR-B1^−/− (upper right) B cells as in SR-B1^+/+ controls (upper left); however, SR-B1^−/− B lymphocytes are nearly unresponsive to CpG stimulation (lower right). E, CpG fails to elicit a NSCC current in SR-B1^−/− lymphocytes, while anti-BCR antibody activates normal CRAC currents in SR-B1^−/− B cells, consistent with a requirement for SR-B1 in CpG-mediated TRPC3-dependent Ca²⁺ entry in primary B cells.