Résumé
The tumour necrosis factor (TNF) family member a proliferation‐inducing ligand (APRIL) is implicated in various B‐cell processes, such as class switch recombination, plasma cell differentiation and plasma cell survival. This was suggested from initial studies analysing B‐cell responses in APRIL‐deficient and transgenic mice, and mice deficient for the TNF receptors of APRIL, transmembrane activator and CAML interactor (TACI) and B‐cell maturation antigen. Here, we present additional evidence for the importance of APRIL in thymus‐independent (TI) B‐cell responses, using APRIL‐deficient and transgenic mice. APRIL‐deficient mice show an impaired immunoglobulin A (IgA) response towards TI B‐cell antigens, whereas APRIL transgenic mice show exaggerated TI B‐cell responses. Moreover, antibody titres to TI antigens were sustained in APRIL transgenic mice for a long time and even increased up to 75 days in the case of IgA against 4‐hydroxy‐nitrophenacetyl‐lipopolysaccharide.