C1q dephosphorylates RAGE and recruits SHP-1 to LAIR-1. Human monocytes were treated with C1q (25 μg/mL) and/or HMGB1 (3 μg/mL) for 15 minutes at 37°C. (A) Total cell lysates were subjected to immunoprecipitation with antibodies to RAGE followed by immunoblotting with antibodies specific for phosphoserine (top) or RAGE (bottom). Numbers indicate the relative signal intensity. N = 3. (B) Total cell lysates were subjected to immunophosphorylation array to observe the phosphorylation of LAIR-1 ITIM motifs. Relative quantification of phosphorylation of LAIR-1 was normalized to control spots (relative fold induction) from 4 independent experiments. (C) Human monocytes were treated with C1 complex (25 μg/mL) and/or HMGB1 (3 μg/mL) for 15 minutes at 37°C. Immunophosphorylation array was performed to observe the phosphorylation of LAIR-1 ITIM motifs. N = 3. *P < .05; **P < .01; ***P < .001 (one-way ANOVA). (D) Total cell lysates were immunoprecipitated with antibodies to LAIR-1 followed by immunoblotting with antibodies for SHP-1 (top) or LAIR-1 (bottom). N = 4. (E) Human monocytes were treated with HMGB1 and/or C1q for 3 hours, and cell lysates were subjected to immunoblotting with antibodies for activated IKKα (P-IKKα, top), p65 (P-p65, middle), or β-actin. N = 3.