Figure 2.

Microvesicle Programing of B Cells

Model for role of TCR-enriched microvesicles in programing B cells for pMHC-linked cell division. High pMHC (affinity or quantity) leads to more TCR-enriched microvesicle transfer in the germinal center light zone. As B cells divide, they symmetrically segregate the TCR-enriched microvesicles and stop dividing when these are lost by division or consumed. This could be a basis for competition between high- and low-affinity B cells in germinal centers. The availability of microvesicles in the germinal center system would control the growth of the structures. The signals in the microvesicles may also include CD40L based on work with related exosomes and central localization of CD40 in the immunological synapse (Blanchard et al., 2002; Boisvert et al., 2004).