Question

You cultured a population of mature B cells in the presence of antigen alone or antigen plus IL-2, IL-4, and IL-5 & neither population of B cells proliferated. What are the missing components?

Answer 1

The culture of the mature B cells in presence of antigen with IL-2,IL-4 and IL-5 , didn't show the proliferation of the B cells due to absence of T-cell effector molecules such as CD40,CD30 ligands (TNF -receptor family member ). In the above condition the activation and expnasion of B cell population were inhibited.

So, the question is how B cells get activated and proliferate ?

The B cell activation occurs by the armed T helper cells ,when they identifies the peptide complex MHC II complex on the surface of Bcells. The armed T helper cells act on the macrophages,recognize the MHCII on B cells initiate the armed T helper cells to secrete the effector molecules that helps in activating B cells and proliferation. T cells effector molecule is nothing but membrane bound molecule of the Tumor necrosis factor family e.g CD40 ligands. CD40 lignad bounds to the CD40 on the surface of the B cells enforces the resting B cells to go through the cell cycle and produces the B -cell response. B-cells get stimulated and proliferated in presence of CD40 and cytokine IL -4. IL-4 are produced by  armed T helper cells and recognize the ligand CD40 on the surface of B cells causes clonal expansion to produce antibody in vivo.