Recognition of SOSIP.R6-IZ-CD40L by antibodies, CD4 and CD40. The SOSIP.R6-IZ-CD40L protein was immunoprecipitated by CD4-IgG2, CD40-Fc, HIVIg, and by antibodies to CD40L, gp120 (b12) or gp41 (2F5), followed by reducing SDS-PAGE and western blot analysis. The left lane contains 50 ng JR-FL gp120 as a loading control. The second sample contains an immunoprecipiation reaction without primary Ab. The lower band visible in lanes 3-7 represents gp120 from residual (< 10%) cleaved protein.