Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19 ؉ / CD27 high /intracellular immunoglobulin G high (IgG high )/HLA-DR high /CD38 high /CD20 ؊ / CD95 ؉ tetanus toxin-specific antibodysecreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19 ؉ /CD27 high /intracellular IgG high /HLA-DR low /CD38 ؉ /CD20 ؊ /CD95 ؉ cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity. IntroductionProtective humoral memory is conferred by stable titers of specific antibodies (Abs) and can last for years. 1 Although primary contact with an antigen (Ag) leads to the formation of Ab-secreting plasma blasts (PBs) with a lifespan of less than 1 week in extrafollicular foci and results in short Ab responses, 2 most Ab-secreting cells (ASCs) generated during secondary (memory) immune response leave the follicles of the secondary lymphoid tissues as PBs. Specific ASCs are later found in the bone marrow (BM), [3][4][5] mucosa-associated tissues, chronically inflamed tissues, 6 or, to a lesser extent, the red pulp of spleens, 7 with the phenotype of mature plasma cells (PCs) and a potential lifespan of more than 18 months. 3,8,9 Indeed, specific Ab titers, mostly of immunoglobulin G (IgG) and IgA subclasses, can be stable for years 10 and are produced mainly by resident PCs of the BM. 10,11 The survival of PCs within the bone marrow (BM) is not an intrinsic capability of these cells but, rather, is regulated by the local microenvironment, 7 which provides a limited number of survival niches for PCs. [12][13][14] Because Abs of the IgG subclass have only a half-life of 3 weeks, 12-14 the survival of PCs in the BM is prerequisite for the maintenance of Ab titers over long time periods (ie, protective immunity and memory). Release from secondary lymphoid organs, migration of PBs to the BM, and competition for the apparently limited number of survival niches with resident PCs generated earlier control the establishment and persistence of protective humoral memory.Chemokines and their receptors are crucial for the control of lymphocyte trafficking. In mouse, CX-chemokine-re...

Recent studies have shown that persistent specific antibody titer is provided by long-lived plasma cells (PC) which constitute a new kind of 'memory-providing cells'. In the present study, we examine the role of antigen for the long-term survival of PC and the maintenance of specific serum antibody titers. Using a novel cytometric technology, to identify and isolate antigen-specific PC, we analyzed long-lived PC of BALB/c mice, during their development (between day 1 and 10) after secondary immunization with ovalbumin (OVA) and in the phase of the established immune reaction. Most if not all OVA-specific PC were generated within a few days after immunization. Within approximately 3 weeks, they matured, as indicated by down-regulation of expression of MHC class II. These PC are long lived and located in spleen and bone marrow. Upon adoptive transfer, OVA-specific PC from bone marrow, but not memory B cells, conferred specific and long-lasting antibody titers to antigen-free IgH syngeneic recipients. In response to antigenic challenge, new OVA-specific antibody-secreting cells were generated from transferred memory B cells. Antibody secretion by long-lived PC was not affected. Our results confirm that persistent antibody titers are provided by long-lived PC, independent of memory B cells and demonstrate that this humoral memory is inert to antigen.

No abstract

In multiple myeloma, the overexpression of receptor activator of nuclear factor kappa B (NF-jB) ligand (RANKL) leads to the induction of NF-jB and activator protein-1 (AP-1)-related osteoclast activation and enhanced bone resorption. The purpose of this study was to examine the molecular and functional effects of proteasome inhibition in RANKL-induced osteoclastogenesis. Furthermore, we aimed to compare the outcome of proteasome versus selective NF-jB inhibition using bortezomib (PS-341) and I-jB kinase inhibitor PS-1145. Primary human osteoclasts were derived from CD14 þ precursors in presence of RANKL and macrophage colony-stimulating factor (M-CSF). Both bortezomib and PS-1145 inhibited osteoclast differentiation in a dose-and time-dependent manner and furthermore, the bone resorption activity of osteoclasts. The mechanisms of action involved in early osteoclast differentiation were found to be related to the inhibition of p38 mitogenactivated protein kinase pathways, whereas the later phase of differentiation and activation occurred due to inhibition of p38, AP-1 and NF-jB activation. The AP-1 blockade contributed to significant reduction of osteoclastic vascular endothelial growth factor production. In conclusion, our data demonstrate that proteasomal inhibition should be considered as a novel therapeutic option of cancer-induced lytic bone disease.