Distinct role of surface lymphotoxin expressed by B cells in the organization of secondary lymphoid tissues.

In order to definitively ascertain the functional contribution of lymphotoxin (LT) expressed by B cells, we produced mice with the LTbeta gene deleted from B cells (B-LTbeta KO mice). In contrast to systemic LTbeta deletion, in B-LTbeta KO mice only splenic microarchitecture was affected, while lymph nodes and Peyer's patches (PP) were normal, except for PP's reduced size. Even though B-LTbeta KO spleens retained a small number of follicular dendritic cells (FDC) which appeared to be dependent on LTbeta produced by T cells, IgG responses to sheep red blood cells were markedly reduced. Thus, the organogenic function of B-LTbeta is almost entirely restricted to spleen, where it supports the correct lymphoid architecture that is critical for an effective humoral immune response.