A centroblast generally refers to an activated B cell that is enlarged (12-18 micrometer) and proliferating in the germinal center of a secondary lymphoid follicle. Centroblasts form following exposure to follicular dendritic cell cytokines, such as IL-6, IL-15, 8D6, and BAFF and stimulation from helper T cell interactions between their CD40 ligand and the B cell CD40 induces centroblasts to express activation-induced cytidine deaminase, leading to somatic hypermutation.
Centroblasts do not express immunoglobulins and are unable to respond to the follicular dendritic cell antigens present in the secondary lymphoid follicles.
References
Centroblasts Wikipedia(Text) CC BY-SA