Coimmunoprecipitation of LRP and β2-integrins. (A) U937 cells were lysed for 1 hour on ice and incubated with Protein A-Sepharose and anti-LRP clone α2-M-R-II2C7 (lane 1) or an isotype control (lane 2) at 4°C overnight. Beads were washed extensively and boiled to release bound proteins. Samples were analyzed by SDS-PAGE and Western blotting using anti-β2 (clone R2E7B) and peroxidase-conjugated rat antimouse. Unstimulated (lane 3) or stimulated (lane 4) cells were lysed and incubated with protein G-Sepharose and an anti-α_M antibody (clone M1/70) (lanes 3 and 4) or an isotype control (lane 5). Precipitated proteins were analyzed by SDS-PAGE and Western blotting using anti-LRP antibody (clone α2-M-R-II4/8). (B) Lipid rafts were isolated from unstimulated or stimulated cells, as described elsewhere.⁴¹  Immunoprecipitations were performed as described in the legend of Figure 3A.