Continuous B Cell Stimulation with CD40 Ligand Induce IgE Isotype Switching

Background: In the T and B cells interaction, activated helper T(Th) cell can stimulate small B cells by the manner of direct physiologic contact each other. The CD40 ligand(CD40L) molecules expressed on the surface membrane of activated Th cells stimulate B cells after binding with bind with B cells. The activated B cells proliferate and differentiate to secrete immunoglobulin IgM, IgG1 and IgE in the presence of lymphokines.

Methods: Female BALB/C and CBA/J mice were used between 8 to 16 weeks of age, Plasma membranes were prepared from CD40 mRNA transfected to Baculovirus Sf-9 cells. B cells were incubated with plasma membranes and various cytokines in the round bottomed 96 well plate for various periods of time and B cells were pulsed and harvested to check the DNA synthesis of B cells. The B cell culture supernatants were assayed for IgM, IgG1, and IgE by using isotype specific sandwich ELISA.

Results: In the kinetics of B cell proliferation, B cell proliferation was peak at day 4 in the presence of interleukin(IL)-4. In the immunoglobuline synthesis, plasma membrane activated B cells secreted IgM, IgG1, and IgE serially in the presence of Th2 type lymphokines. IgM was produced from second day, IgG1 was third day, and IgE was fifth day of culture.

Conclusions: The molecule of CD40L play a major role to activate B cells in the T and B cell interaction. The IL-4 and IL-5 are required to proliferate B cells and induce IgM, and isotype switching to secrete IgG1 and IgE. The dose and duration of reactions with antigen and cytokines play an important role in the B cell proliferation and differentiation.