Liposome aggregation mediated by CEACAM1. (A) Aggregation of D(1–4) and D(2–4) proteoliposomes with protein/lipid ratios varying from 1:10 to 1:90 (wt/wt) measured as turbidity at 595 nm at various times after protein addition. (B) 2D electron microscopic images of naked liposomes, D(1–4) proteoliposomes, and D(2–4) proteoliposomes (protein/lipid ratio 1:5). The small black dots indicate 10-nm colloidal gold particles. Bars, 100 nm.