Impaired binding of CD300a-Ig Q94, a SNP linked to psoriasis susceptibility. (A) Binding of CD300a-Ig Q94 to dead PBLs. Purified CD300a-Ig proteins were incubated with starved PBLs and their binding to 7-AAD⁺ cells after adding anti–human Ig FITC was determined by flow cytometry. LAIR1-Ig was used as a negative control protein. Numbers in the dot plots are the percentage of 7-AAD⁺ PBLs that bind the fusion proteins. A representative experiment is shown. Bar graph represents the average ± SEM. Results shown are from 5 independent experiments. (B) Binding of CD300a-Ig proteins to liposomes. Liposomes of specified compositions (x-axis) were prepared and coupled to a L1 biosensor. See the supplemental Methods for specifics of liposome composition. The binding of CD300a-Ig R94 (wild-type), CD300a-Ig Q94 (SNP), CD300a-Ig D98A (not binding mutant) and LAIR-1-Ig (negative control) was analyzed by allowing the proteins to pass through the L1 sensor. The binding (RU) for plateau values is shown. The RU were plotted after subtracting from the buffer control. Bar graph represents the average ± SEM. Results shown are from 2 independent experiments. (C) Binding of CD300a-Ig Q94 to purified lipids. Aminophospholipids PE and PS were coupled to 96-well plates as described in supplemental Methods. A sandwich ELISA was performed with the Ig-fusion proteins at different concentrations. The optical density at 450 nm was determined. Data shown are representative of 2 independent experiments.