Antigenicity of HIV-1 CA. We immunized mice with purified CA as described in Methods. The sera from immunized mice were serially diluted and subjected to indirect ELISA. The pre-immune serum served as the negative control (A). 293T cells were transfected with the pNL4-3 plasmid and cell lysates were analyzed by SDS-PAGE and Western blotting using serum from CA-immunized mice (B). Lane M1, MagicMark XP Western Protein Standard; Lane 1, mock-transfected 293T cell lysate; Lane 2, pNL4.3-transfected 293T cell lysate; Lane 3, purified CA (10 ng); Lane 4, purified CA (100 ng).