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. Author manuscript; available in PMC: 2012 May 1.
Published in final edited form as: Trends Immunol. 2011 Mar 16;32(5):202–211. doi: 10.1016/j.it.2011.02.004

Figure 2.

Figure 2

Modalities of B cell activation by BAFF and APRIL. (a) Constitutive DC and stromal cell (SC) release of soluble BAFF trimers (upper half) stimulates survival in follicular (FO) and MZ B cells. BAFF trimers predominantly elicit signals through BAFF-R. Constitutive DC and SC release of APRIL (bottom half) supports plasma cell survival in the bone marrow (BM) and perhaps intestinal lamina propria (LP). APRIL trimers predominantly signal through BCMA. (b) TLR-induced DC and stromal cell (SC) release of abundant BAFF and APRIL trimers causes formation of virus-like BAFF multimers and HSPG-bound APRIL multimers, which induce IgM production, IgG IgA and IgE CSR, Ig secretion, survival and differentiation by signaling through TACI as well as BCMA and BAFF-R in B cells and plasma cells. HSPGs are in particularly expressed on SCs and plasma cells. APRIL, a proliferation-inducing ligand; BAFF, B cell-activating factor of the TNF family; BCMA, B cell maturation antigen; CSR, class switch recombination; DC, dendritic cell; HSPG, heparan sulphate proteoglycan; MZ, marginal zone; TACI, transmembrane activator and calcium-modulating ciclophilin-ligand interactor; TLR, Toll-like receptor.