Cellular Basis of Antibody Maintenance: Heterogeneity of the Bone Marrow Plasma Cell Pool

Plasma cells are the immune system cells responsible for producing antibodies, the key mediators of protective humoral immunity. Long-lived plasma cells (PC) are thought to be responsible for maintaining antibody titers and are believed to populate unique survival niches in the bone marrow (BM). Current models predict that bone marrow plasma cells (BM PC) consist chiefly of long-lived, slowly renewing cells. In chapter 2, we show the turnover rate of the BM PC pool to be much higher than predicted by these models; in fact, more than 50% of BM PC exhibit characteristics of recently formed PC. Intriguingly, these B220+ PC do not appear to be cycling and are depleted upon ablation of peripheral B cell pools. In chapter 3, we extend our studies to antigen-induced responses. We find that very long-term maintenance of the antigen-specific BM PC pool is dependent on a CD40-independent B cell precursor. Despite the rapid turnover rate exhibited by B220+ BM PC, antigen-induced antibody secreting cells are found within this population for more than 100 days post-immunization. These cells secrete exclusively low affinity, unswitched, κ type antibodies in sharp contrast to the high affinity, isotype switched cells found within the slowly renewing BM PC pool. Finally, we identify a population of rapidly renewing memory B cells that appear to be the precursors of the B220+ BM PC. Together these data suggest that BM niches are continuously repopulated by newly generated plasma cells long after antigenic exposure and identify the memory B cell precursors of BM PC

The ion transporter Na⁺-K⁺-ATPase enables pathological B cell survival in the kidney microenvironment of lupus nephritis

The kidney is a comparatively hostile microenvironment characterized by highsodium concentrations; however, lymphocytes infiltrate and survive therein in autoimmune diseases such as lupus. The effects of sodium-lymphocyte interactions on tissue injury in autoimmune diseases and the mechanisms used by infiltrating lymphocytes to survive the highsodium environment of the kidney are not known. Here, we show that kidneyinfiltrating B cells in lupus adapt to elevated sodium concentrations and that expression of sodium potassium adenosine triphosphatase (Na+-K+-ATPase) correlates with the ability of infiltrating cells to survive. Pharmacological inhibition of Na+-K+-ATPase and genetic knockout of Na+-K+-ATPase γ subunit resulted in reduced B cell infiltration into kidneys and amelioration of proteinuria. B cells in human lupus nephritis biopsies also had high expression of Na+-K+-ATPase. Our study reveals that kidney-infiltrating B cells in lupus initiate a tissue adaption program in response to sodium stress and identifies Na+-K+-ATPase as an organ-specific therapeutic target

TIM-1 and TIM-4 Glycoproteins Bind Phosphatidylserine and Mediate Uptake of Apoptotic Cells

SummaryThe T cell immunoglobulin mucin (TIM) proteins regulate T cell activation and tolerance. Here we showed that TIM-4 is expressed on human and mouse macrophages and dendritic cells, and both TIM-4 and TIM-1 specifically bound phosphatidylserine (PS) on the surface of apoptotic cells but not any other phospholipid tested. TIM-4+ peritoneal macrophages, TIM-1+ kidney cells, and TIM-4- or TIM-1-transfected cells efficiently phagocytosed apoptotic cells, and phagocytosis could be blocked by TIM-4 or TIM-1 monoclonal antibodies. Mutations in the unique cavity of TIM-4 eliminated PS binding and phagocytosis. TIM-4 mAbs that blocked PS binding and phagocytosis mapped to epitopes in this binding cavity. These results show that TIM-4 and TIM-1 are immunologically restricted members of the group of receptors whose recognition of PS is critical for the efficient clearance of apoptotic cells and prevention of autoimmunity

Lasting Antibody Responses Are Mediated by a Combination of Newly Formed and Established Bone Marrow Plasma Cells Drawn from Clonally Distinct Precursors

WOS: 000345023400026PubMed ID: 25326027Current models hold that serum Ab titers are maintained chiefly by long-lived bone marrow (BM) plasma cells (PCs). In this study, we characterize the role of subpopulations of BM PCs in long-term humoral responses to T cell-dependent Ag. Surprisingly, our results indicate that 40-50% of BM PCs are recently formed cells, defined, in part, by rapid steady-state turnover kinetics and secretion of low-affinity IgM Abs. Further, for months after immunization with a hapten-protein conjugate, newly formed Ag-induced, IgM-secreting BM PCs were detected in parallel with longer-lived IgG-secreting cells, suggesting ongoing and parallel input to the BM PC pool from two distinct pools of activated B cells. Consistent with this interpretation, IgM and IgG Abs secreted by cells within distinct PC subsets exhibited distinct L chain usage. We conclude that long-term Ab responses are maintained by a dynamic BM PC pool composed of both recently formed and long-lived PCs drawn from clonally disparate precursors.National Institutes of HealthUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [R01AI097590, F30HL112628, T32CA009140, T32 AI070099]This work was supported by National Institutes of Health Grants R01AI097590 (to DA.), F30HL112628 (to I.C.), T32CA009140 (to D.D.J.), and T32 AI070099 (to A.B.)

Substance P (SP) enhances CCL5-induced chemotaxis and intracellular signaling in human monocytes, which express the truncated neurokinin-1 receptor (NK1R)

Substance P (SP) is a potent modulator of monocyte/macrophage function. The SP-preferring receptor neurokinin-1 receptor (NK1R) has two forms: a full-length NK1R (NK1R-F) isoform and a truncated NK1R (NK1R-T) isoform, which lacks the terminal cytoplasmic 96-aa residues. The distribution of these receptor isoforms in human monocytes is not known. We previously identified an interaction among SP, NK1R, and HIV viral strains that use the chemokine receptor CCR5 as a coreceptor, suggesting crosstalk between NK1R and CCR5. The purpose of this study was to determine which form(s) of NK1R are expressed in human peripheral blood monocytes and to determine whether SP affects proinflammatory cellular responses mediated through the CCR5 receptor. Human peripheral blood monocytes were found to express NK1R-T but not NK1R-F. SP interactions with NK1R-T did not mobilize calcium (Ca2+), but SP mobilized Ca2+ when the NK1R-F was transfected into monocytes. However, the NK1R-T was functional in monocytes, as SP enhanced the CCR5 ligand CCL5-elicited Ca2+ mobilization, a response inhibited by the NK1R antagonist aprepitant. SP interactions with the NK1R-T also enhanced CCL5-mediated chemotaxis, which was ERK1/2-dependent. NK1R-T selectively activated ERK2 but increased ERK1 and ERK2 activation by CCL5. Activation of NK1R-T elicited serine phosphorylation of CCR5, indicating that crosstalk between CCL5 and SP may occur at the level of the receptor. Thus, NK1R-T is functional in human monocytes and activates select signaling pathways, and the NK1R-T-mediated enhancement of CCL5 responses does not require the NK1R terminal cytoplasmic domain

WDR11, a WD Protein that Interacts with Transcription Factor EMX1, Is Mutated in Idiopathic Hypogonadotropic Hypogonadism and Kallmann Syndrome

By defining the chromosomal breakpoint of a balanced t(10;12) translocation from a subject with Kallmann syndrome and scanning genes in its vicinity in unrelated hypogonadal subjects, we have identified WDR11 as a gene involved in human puberty. We found six patients with a total of five different heterozygous WDR11 missense mutations, including three alterations (A435T, R448Q, and H690Q) in WD domains important for β propeller formation and protein-protein interaction. In addition, we discovered that WDR11 interacts with EMX1, a homeodomain transcription factor involved in the development of olfactory neurons, and that missense alterations reduce or abolish this interaction. Our findings suggest that impaired pubertal development in these patients results from a deficiency of productive WDR11 protein interaction