Centroblasts

A centroblast generally refers to an activated B cell that is enlarged (12-18 micrometer) and proliferating in the germinal center of a lymphoid follicle.[1] 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.

Morphologically, centroblasts are large lymphoid cells containing a moderate amount of cytoplasm, round to oval vesicular (i.e. containing small fluid-filled sacs) nuclei, vesicular chromatin, and 2–3 small nucleoli often located adjacent to the nuclear membrane. They are derived from B cells. Immunoblasts are distinguished from centroblasts by being B cell-derived lymphoid cells that have moderate-to-abundant basophilic cytoplasm and a prominent, centrally located, trapezoid-shaped single nucleolus which often has fine strands of chromatin attached to the nuclear membrane (‘spider legs’). In some cases, immunoblasts can show some morphologic features of plasma cells.[2]

Centroblasts do not express immunoglobulins and are unable to respond to the follicular dendritic cell antigens present in the secondary lymphoid follicles.