Splenectomy of rats selectively reduces lymphocyte function-associated antigen 1 and intercellular adhesion molecule 1 expression on B-cell subsets in blood and lymph nodes

Splenectomy increases the number of B cells in the blood of humans and anim als. It is unknown whether this is due to changes in migration, proliferati on, or both. The numbers of naive (IgD(+)IgM(+)), memory (IgD(-)IgM(high)), newly formed (IgM(high)CD90(high)), early recirculating follicular (IgM(lo w)CD90(high)), recirculating follicular (IgM(low)CD90(-)), and marginal zon e (IgM(high)CD90(-)) phenotype B cells were determined in control and splen ectomized rats by flow cytometry. All subsets increased significantly in th e blood after splenectomy. Because surface molecules are involved in the re gulation of migration and proliferation, their expression (lymphocyte funct ion-associated antigen I [LFA-1], intercellular adhesion molecule 1 (ICAM-1 ), L-selectin, alpha (4)-integrins, CD44, major histocompatability complex class II, interleukin 2 receptor-alpha chain) was determined on B- and T-ce ll subsets of both groups. B cells, but not T cells, showed a significantly reduced LFA-1 and ICAM-1 expression in blood and lymph nodes, whereas the expression of the other surface molecules analyzed remained unchanged. The down-regulation of these molecules did not influence the adherence of B cel ls to high endothelial venules in vitro. In vivo, however, 1(low)-expressin g B cells migrated significantly faster through lymph nodes (ICAM-1(low) 41 +/- 5 hours versus ICAM-1(high) 58 +/- 3 hours), whereas proliferation of B cells in bone marrow, lymph node, and blood remained unchanged. Thus, the presence of one organ is necessary for appropriate expression of LFA-1 and ICAM-1 on B cells in other, distant organs. The more rapid transit of ICAM -1(low) B cells through lymph nodes may be responsible for the increased B- cell number in the blood after splenectomy. (C) 2001 by The American Societ y of Hematology.