B Cell Isotype Switching Is Dependent upon the Duration of B Cell Activation and Dose of Antigen

Rationale: In the T and B cells interaction, the CD40 ligand molecules of the  activated helper T cells stimulate B cells by the manner of direct physiologic contact. The activated B cells proliferate and differentiate to secrete IgA, IgM, IgG and IgE in the presence of lymphokines.

Methods: Female BALB/C mice were used between 8 to 16 weeks of age. Plasma membranes were prepared from CD40 mRNA transfected to Sf-9 cells. High and low concentration of CFSE-labeled small B cells were incubated with plasma membranes with Th2 cell culture supernatants in the round bottomed 96 well plate for various periods and analyzed by flow cytometry. B cell culture supernatants were assayed for IgM, IgG1, and IgE according to the concentrations of B cells and the duration of culture by using sandwich ELISA

Results: B cells were divided from second day of culture and up to more than eight times on fifth day. The numbers of cell division cycle were almost same in low and high B cell concentration groups. B cells secreted IgM, IgG1 and IgE serially from the third division. But it was more prominent in low B cell concentration groups than higher B cell groups.   

Conclusions: B cell isotype switching from IgM to IgG1 and IgE was correlated with number of cell divisions. Finally, the dose of antigen and duration of B cell stimulation play an important role in the B cell division cycles linked with isotype switching.