Complexity within the plasma cell compartment of mice deficient in both E- and P-selectin: implications for plasma cell differentiation.

Antibody-secreting plasma cells represent the critical end-stage effector cells of the humoral immune response. Here, we show that several distinct plasma cell subsets are concurrently present in the lymph nodes, spleen, and bone marrow of mice deficient in both E- and P-selectin. One of these subsets was a B220-negative immunoglobulin g (IgG) plasma cell population expressing low to negative surface levels of syndecan-1. Examination of the chemotactic responsiveness of IgG plasma cell subsets revealed that migration toward stromal cell-derived factor 1/CXC ligand 12 (SDF-1/CXCL12) was primarily limited to the B220-lo subset regardless of tissue source. Although B220-negative plasma cells did not migrate efficiently in response to CXCL12 or to other chemokines for which receptor mRNA was expressed, these cells expressed substantial surface CXC chemokine receptor-4 (CXCR4), and CXCL12 stimulation rapidly induced extracellular signal regulated kinase 1 (ERK1)/ERK2 phosphorylation, demonstrating that CXCR4 retained signaling capacity. Therefore, B220-negative plasma cells exhibit a selective uncoupling of chemokine receptor expression and signaling from migration. Taken together, our findings document the presence of significant heterogeneity within the plasma cell compartment, which suggests a complex step-wise scheme of plasma cell differentiation in which the degree of differentiation and tissue location can influence the chemotactic responsiveness of IgG plasma cells.