CD27 antigen negative expression indicates poor prognosis in newly diagnosed multiple myeloma.

To investigate the role of CD27 in multiple myeloma(MM), bone marrow samples from 165 newly diagnosed MM were analysed by flow cytometry. CD27- group (n = 93) had higher level of plasma cell proportion (37.00% vs 22.50%, p < .05), ß2-MG (5.42 vs 3.20 mg/L, p < .05), calcium (2.45 vs 2.28 mmol/L, p < .05),higher percentage of ISS stage III (49.46% vs 22.22%, p < .05) and patients with ≥2 high-risk cytogenetics (24.73% vs 15.28%, p < .05) than CD27+ group (n = 72). After 4 cycles of chemotherapy, the overall response rate in CD27- group were lower than CD27+ group (56.67% vs 73.02%,p < .05). After a median follow-up of 18 months, progression-free survival was significantly shorter in CD27- group than in CD27+ group (22 vs 40 months, p < .05), so was overall survival (median OS not reached, p < .05). Gene sequencing showed more adverse mutations in CD27- group than CD27+ group.

Blockade of costimulatory CD27/CD70 pathway promotes corneal allograft survival.

PURPOSE: To determine whether the CD27/CD70 pathway plays a significant role in corneal allograft rejection by investigating the effect of blocking the CD27/CD70 pathway by anti-CD70 antibody on corneal allograft survival. METHODS: Orthotopic penetrating keratoplasty was performed using C57BL/6 donor grafts and BALB/c recipients. Expression of CD27 and CD70 on rejected cornea was examined by immunohistochemistry. Corneal transplant recipients received intraperitoneal injection of anti-CD70 antibody (FR70) or control rat IgG. Alloreactivity was measured by mixed lymphoid reaction (MLR) in recipients administered control rat IgG and those administered anti-CD70 antibody. Corneal expression of IFN-γ and IL-12 was also examined in both groups. Graft opacity was assessed over an 8-week period and graft survival was evaluated using Kaplan-Meier survival curves. Proportion of CD4+CD44+ memory T cells in lymph nodes was measured by flow cytometry. RESULTS: CD4+CD27+ cells and CD11c+CD70+ cells were present in rejected cornea. Anti-CD70 antibody administration suppressed alloreactivity in corneal allograft recipients, and inhibited IFN-γ expression in recipient cornea (p < 0.05). Anti-CD70 antibody suppressed opacity score of recipient cornea and prolonged corneal allograft survival (p < 0.05). Proportion of CD4+CD44+ memory T cells in recipient lymph nodes was reduced by anti-CD70 antibody treatment. CONCLUSION: The CD27/CD70 pathway plays a significant role in corneal allograft rejection by initiating alloreactive Th1 cells and preserving memory T cells. Anti-CD70 antibody administration prolongs corneal allograft survival indicating the potential therapeutic effect of CD27/CD70 pathway blockade on corneal allograft rejection.

The majority of human memory B cells recognizing RhD and tetanus resides in IgM+ B cells.

B cell memory to T cell-dependent (TD) Ags are considered to largely reside in class-switched CD27(+) cells. However, we previously observed that anti-RhD (D) Igs cloned from two donors, hyperimmunized with D(+) erythrocytes, were predominantly of the IgM isotype. We therefore analyzed in this study the phenotype and frequency of D- and tetanus toxoid-specific B cells by culturing B cells in limiting dilution upon irradiated CD40L-expressing EL4.B5 cells and testing the culture supernatant. Most Ag-specific B cells for both TD Ags were found to reside in the IgM-expressing B cells, including CD27(-) B cells, in both hyperimmunized donors and nonhyperimmunized volunteers. Only shortly after immunization a sharp increase in Ag-specific CD27(+)IgG(+) B cells was observed. Next, B cells were enriched with D(+) erythrocyte ghosts and sorted as single cells. Sequencing of IGHV, IGLV, IGKV, and BCL6 genes from these D-specific B cell clones demonstrated that both CD27(-)IgM(+) and CD27(+)IgM(+) B cells harbored somatic mutations, documenting their Ag-selected nature. Furthermore, sequencing revealed a clonal relationship between the CD27(-)IgM(+), CD27(+)IgM(+), and CD27(+)IgG(+) B cell subsets. These data strongly support the recently described multiple layers of memory B cells to TD Ags in mice, where IgM(+) B cells represent a memory reservoir which can re-enter the germinal center and ensure replenishment of class-switched memory CD27(+) B cells from Ag-experienced precursors.

Triggering of NF-κB in cytokine-matured human DCs generates superior DCs for T-cell priming in cancer immunotherapy.

Understanding the signaling that governs the immunogenicity of human dendritic cells (DCs) is a prerequisite for improving DC-based therapeutic vaccination strategies, in which the ability of DCs to induce robust and lasting Ag-specific CTL responses is of critical importance. Cytokine-matured DCs are regularly used, but to induce memory-type CTLs, they require additional activation stimuli, such as CD4+ T-cell help or TLR activation. One common denominator of these stimuli is the activation of NF-κB. Here, we show that human monocyte-derived, cytokine cocktail-matured DCs transfected with constitutively active mutants of IκB kinases (caIKKs) by mRNA electroporation, further upregulated maturation markers, and secreted enhanced amounts of cytokines, including IL-12p70, which was produced for more than 48 h after transfection. Most importantly, cytotoxic T cells induced by caIKK-transfected DCs combined high CD27 expression, indicating a more memory-like phenotype, and a markedly enhanced secondary expandability with a high lytic capacity. In contrast, CTLs primed and expanded with unmodified cytokine cocktail-matured DCs did not maintain their proliferative capacity upon repetitive stimulations. We hypothesize that "designer" DCs expressing constitutively active IκB kinases will prove highly immunogenic also in vivo and possibly emerge as a new strategy to improve the clinical efficacy of therapeutic vaccinations against cancer and other chronic diseases.

Increased Syk phosphorylation leads to overexpression of TRAF6 in peripheral B cells of patients with systemic lupus erythematosus.

OBJECTIVE: Activation of B cells is a hallmark of systemic lupus erythematosus (SLE). Syk and TRAF6 are key signaling molecules in B-cell activation through BCR and CD40/TLR, respectively. Nevertheless, whether expression of Syk and TRAF6 is altered in SLE B cells remains unknown. METHODS: Phosphorylation and/or expression of Syk and TRAF6 were analyzed by flow cytometry in peripheral blood mononuclear cells isolated from SLE patients. RESULTS: Pronounced phosphorylation and expression of Syk were noted in B cells from SLE patients compared with healthy donors. Levels of Syk phosphorylation correlated with the disease activity score. TRAF6 was significantly over-expressed in B cells of SLE patients as compared with healthy donors, and significant correlation of levels of TRAF6 expression and Syk phosphorylation was observed in SLE patients. Levels of TRAF6 expression were more pronounced in CD27+ memory B cells than in CD27-naïve B cells. In vitro treatment of SLE B cells with a Syk inhibitor (BAY61-3606) reduced Syk phosphorylation as well as TRAF6 expression. CONCLUSION: Our results suggest that the activated Syk-mediated TRAF6 pathway leads to aberrant activation of B cells in SLE, and also highlight Syk as a potential target for B-cell-mediated processes in SLE.

Epstein-Barr virus infection of naïve B cells in vitro frequently selects clones with mutated immunoglobulin genotypes: implications for virus biology.

Epstein-Barr virus (EBV), a lymphomagenic human herpesvirus, colonises the host through polyclonal B cell-growth-transforming infections yet establishes persistence only in IgD⁺ CD27⁺ non-switched memory (NSM) and IgD⁻ CD27⁺ switched memory (SM) B cells, not in IgD⁺ CD27⁻ naïve (N) cells. How this selectivity is achieved remains poorly understood. Here we show that purified N, NSM and SM cell preparations are equally transformable in vitro to lymphoblastoid cells lines (LCLs) that, despite upregulating the activation-induced cytidine deaminase (AID) enzyme necessary for Ig isotype switching and Ig gene hypermutation, still retain the surface Ig phenotype of their parental cells. However, both N- and NSM-derived lines remain inducible to Ig isotype switching by surrogate T cell signals. More importantly, IgH gene analysis of N cell infections revealed two features quite distinct from parallel mitogen-activated cultures. Firstly, following 4 weeks of EBV-driven polyclonal proliferation, individual clonotypes then become increasingly dominant; secondly, in around 35% cases these clonotypes carry Ig gene mutations which both resemble AID products and, when analysed in prospectively-harvested cultures, appear to have arisen by sequence diversification in vitro. Thus EBV infection per se can drive at least some naïve B cells to acquire Ig memory genotypes; furthermore, such cells are often favoured during an LCL's evolution to monoclonality. Extrapolating to viral infections in vivo, these findings could help to explain how EBV-infected cells become restricted to memory B cell subsets and why EBV-driven lymphoproliferative lesions, in primary infection and/or immunocompromised settings, so frequently involve clones with memory genotypes.

CD45RA-Foxp3(low) non-regulatory T cells in the CCR7-CD45RA-CD27+CD28+ effector memory subset are increased in synovial fluid from patients with rheumatoid arthritis.

Increased numbers of regulatory T (Treg) cells are found in synovial fluid from patients with rheumatoid arthritis (RASF) compared with peripheral blood. However, Treg cells in RASF have been shown to have a decreased capacity to suppress T cells. Here we phenotypically classified CD4+ T cells in RASF into six subsets based on the expression of CD45RA, CCR7, CD27 and CD28, and demonstrated that the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in synovial fluid compared with peripheral blood. In addition, the proportion of Foxp3+ Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Furthermore, most of the Foxp3+ Treg cells in RASF were non-suppressive CD45RA-Foxp3(low) non-Treg cells, and the frequency of the non-Treg cells in the CCR7-CD45RA-CD27+CD28+ TEM subset was significantly increased in RASF. Our findings suggest that the pro-inflammatory environment in RA joints may induce the increase of CD45RA-Foxp3(low) non-Treg cells in synovial fluid.

Unlike αß T cells, γδ T cells, LTi cells and NKT cells do not require IRF4 for the production of IL-17A and IL-22.

Apart from conventional CD4(+) Th17 cells, the cytokines IL-17A and IL-22 can also be produced by γδ T cells, NK cells and lymphoid tissue inducer (LTi) cells. Th17 cells develop from precursor cells after T-cell receptor stimulation in the presence of TGF-ß, IL-6 and IL-23. In contrast, a subset of γδ T cells ("γδT17") is committed for fast IL-17 production already in the thymus; however, γδ T cells can also produce IL-17 after prolonged in vitro stimulation via their γδ T-cell receptor plus IL-23. Here, we show that γδ T-, LTi- and NKT cells differ extensively from Th17 cells in their signalling requirements for the generation of IL-17A and IL-22. While production of these cytokines by Th17 cells totally depends on the transcription factor interferon regulatory factor 4 (IRF4), IRF4 is irrelevant in the other cell types. As for γδ T cells, this finding pertains to both thymic commitment and prolonged in vitro culture. Furthermore, IL-17A-producing γδ T cells accumulate in the central nervous system of IRF4 deficient (Irf4(-/-)) mice during experimental autoimmune encephalomyelitis. IL-17A-producing WT and Irf4(-/-) γδ T cells equally express CCR6 and lack CD27. The underlying IRF4-independent pathway partially involves STAT3 during in vitro stimulation.

CD27+ B cells from a subgroup of common variable immunodeficiency patients are less sensitive to apoptosis rescue regardless of interleukin-21 signalling.

Common variable immunodeficiency (CVID) is a primary immunodeficiency characterized by hypogammaglobulinaemia and recurrent infections. Although the underlying cause is unknown, B cells from most CVID patients fail to differentiate to memory or plasma cells. We investigated if increased apoptosis could influence the fate of B cells. For this purpose we activated purified B lymphocytes of CVID patients with a surrogate T-dependent (anti-CD40) or T-independent [cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODN) or anti-immunoglobulin (Ig)M)] stimulus with or without interleukin (IL)-21. We found that CD27(+) B cells were more sensitive than CD27(-) B cells to spontaneous apoptosis and less sensitive to rescue from apoptosis. The addition of IL-21 down-modulated the protective effect of all the stimuli on CD27(-) B cells and the protective effect of CpG-ODN and anti-IgM on CD27(+) B cells. In contrast, IL-21 rescued unstimulated CD27(-) B cells and improved the rescue of anti-CD40-stimulated CD27(+) B cells. When we compared patients and controls, mainly CD27(+) B cells from MB0 patients were less sensitive to rescue from apoptosis than those from MB1 patients and controls after activation, irrespective of the IL-21 effect. Increased apoptosis during an immune response could result in lower levels of immunoglobulin production in these patients.

Reversible senescence in human CD4+CD45RA+CD27- memory T cells.

Persistent viral infections and inflammatory syndromes induce the accumulation of T cells with characteristics of terminal differentiation or senescence. However, the mechanism that regulates the end-stage differentiation of these cells is unclear. Human CD4(+) effector memory (EM) T cells (CD27(-)CD45RA(-)) and also EM T cells that re-express CD45RA (CD27(-)CD45RA(+); EMRA) have many characteristics of end-stage differentiation. These include the expression of surface KLRG1 and CD57, reduced replicative capacity, decreased survival, and high expression of nuclear γH2AX after TCR activation. A paradoxical observation was that although CD4(+) EMRA T cells exhibit defective telomerase activity after activation, they have significantly longer telomeres than central memory (CM)-like (CD27(+)CD45RA(-)) and EM (CD27(-)CD45RA(-)) CD4(+) T cells. This suggested that telomerase activity was actively inhibited in this population. Because proinflammatory cytokines such as TNF-α inhibited telomerase activity in T cells via a p38 MAPK pathway, we investigated the involvement of p38 signaling in CD4(+) EMRA T cells. We found that the expression of both total and phosphorylated p38 was highest in the EM and EMRA compared with that of other CD4(+) T cell subsets. Furthermore, the inhibition of p38 signaling, especially in CD4(+) EMRA T cells, significantly enhanced their telomerase activity and survival after TCR activation. Thus, activation of the p38 MAPK pathway is directly involved in certain senescence characteristics of highly differentiated CD4(+) T cells. In particular, CD4(+) EMRA T cells have features of telomere-independent senescence that are regulated by active cell signaling pathways that are reversible.

Enhanced and sustained CD8+ T cell responses with an adenoviral vector-based hepatitis C virus vaccine encoding NS3 linked to the MHC class II chaperone protein invariant chain.

Potent and broad cellular immune responses against the nonstructural (NS) proteins of hepatitis C virus (HCV) are associated with spontaneous viral clearance. In this study, we have improved the immunogenicity of an adenovirus (Ad)-based HCV vaccine by fusing NS3 from HCV (Strain J4; Genotype 1b) to the MHC class II chaperone protein invariant chain (Ii). We found that, after a single vaccination of C57BL/6 or BALB/c mice with Ad-IiNS3, the HCV NS3-specific CD8(+) T cell responses were significantly enhanced, accelerated, and prolonged compared with the vaccine encoding NS3 alone. The AdIiNS3 vaccination induced polyfunctional CD8(+) T cells characterized by coproduction of IFN-γ, TNF-α and IL-2, and this cell phenotype is associated with good viral control. The memory CD8(+) T cells also expressed high levels of CD27 and CD127, which are markers of long-term survival and maintenance of T cell memory. Functionally, the AdIiNS3-vaccinated mice had a significantly increased cytotoxic capacity compared with the AdNS3 group. The AdIiNS3-induced CD8(+) T cells protected mice from infection with recombinant vaccinia virus expressing HCV NS3 of heterologous 1b strains, and studies in knockout mice demonstrated that this protection was mediated primarily through IFN-γ production. On the basis of these promising results, we suggest that this vaccination technology should be evaluated further in the chimpanzee HCV challenge model.

Plasmodium falciparum malaria in the Peruvian Amazon, a region of low transmission, is associated with immunologic memory.

The development of clinical immunity to Plasmodium falciparum malaria is thought to require years of parasite exposure, a delay often attributed to difficulties in developing protective antibody levels. In this study, we evaluated several P. falciparum vaccine candidate antigens, including apical membrane antigen 1 (AMA-1), circumsporozoite protein (CSP), erythrocyte binding antigen 175 (EBA-175), and the 19-kDa region of merozoite surface protein 1 (MSP1(19)). After observing a more robust antibody response to MSP1(19), we evaluated the magnitude and longevity of IgG responses specific to this antigen in Peruvian adults and children before, during, and after P. falciparum infection. In this low-transmission region, even one reported prior infection was sufficient to produce a positive anti-MSP1(19) IgG response for >5 months in the absence of reinfection. We also observed an expansion of the total plasmablast (CD19(+) CD27(+) CD38(high)) population in the majority of individuals shortly after infection and detected MSP1-specific memory B cells in a subset of individuals at various postinfection time points. This evidence supports our hypothesis that effective antimalaria humoral immunity can develop in low-transmission regions.

Reduced naive CD4 T cell numbers and impaired induction of CD27 in response to T cell receptor stimulation reflect a state of immune activation in chronic hepatitis C virus infection.

BACKGROUND: Chronic hepatitis C virus (HCV) infection is characterized by reduced numbers of functional HCV-specific T cells. In addition, chronically HCV-infected individuals have reduced response to vaccine. Alterations in naive CD4 T cell phenotype or function may contribute to these immune impairments. METHODS: Using flow cytometric analysis and enzyme-linked immunospot assay, we examined peripheral naive CD4 T cell phenotype and function in chronically HCV-infected patients and control subjects. RESULTS: We observed significantly lower absolute cell numbers of naive CD4 T cells in HCV-infected patients, localized to the CD127(+)CD25(low/-) and CD31(+) (RTE) subsets. Moreover, we found greater percentages of naive cells expressing CD25 and KI67 in HCV-infected patients, consistent with immune activation, further supported by higher plasma sCD27 levels. Functional analysis revealed an intact interferon-γ response to allogeneic B cell stimulus. However, after direct TCR stimulation, naive CD4 T cells from HCV-infected patients had altered up-regulation of KI67 and CD25 and less CD27 expression. The latter was associated with elevated baseline activation state. In addition, naive CD4 T cells from HCV-infected patients were more susceptible to cell death. CONCLUSIONS: These numerical and functional defects may contribute to inadequate formation of virus and neoantigen-specific T cell responses during chronic HCV infection.

Cytomegalovirus infection induces the accumulation of short-lived, multifunctional CD4+CD45RA+CD27+ T cells: the potential involvement of interleukin-7 in this process.

The relative roles that ageing and lifelong cytomegalovirus (CMV) infection have in shaping naive and memory CD4+ T-cell repertoires in healthy older people is unclear. Using multiple linear regression analysis we found that age itself is a stronger predictor than CMV seropositivity for the decrease in CD45RA+ CD27+ CD4+ T cells over time. In contrast, the increase in CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells is almost exclusively the result of CMV seropositivity, with age alone having no significant effect. Furthermore, the majority of the CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells in CMV-seropositive donors are specific for this virus. CD45RA+ CD27⁻ CD4+ T cells have significantly reduced CD28, interleukin-7 receptor α (IL-7Rα) and Bcl-2 expression, Akt (ser473) phosphorylation and reduced ability to survive after T-cell receptor activation compared with the other T-cell subsets in the same donors. Despite this, the CD45RA+ CD27⁻ subset is as multifunctional as the CD45RA⁻ D27+ and CD45RA⁻ CD27⁻ CD4+ T-cell subsets, indicating that they are not an exhausted population. In addition, CD45RA+ CD27⁻ CD4+ T cells have cytotoxic potential as they express high levels of granzyme B and perforin. CD4+ memory T cells re-expressing CD45RA can be generated from the CD45RA⁻ CD27+ population by the addition of IL-7 and during this process these cells down-regulated expression of IL-7R and Bcl-2 and so resemble their counterparts in vivo. Finally we showed that the proportion of CD45RA+ CD27⁻ CD4+ T cells of multiple specificities was significantly higher in the bone marrow than the blood of the same individuals, suggesting that this may be a site where these cells are generated.

Continuous CD27 triggering in vivo strongly reduces NK cell numbers.

NK cells are important mediators of the early defense. In mice, immature and mature NK (mNK) cells constitutively express the TNF receptor family member CD27; however, mNK cells eventually lose CD27 expression and become resting NK cells. Interaction of CD27 with its ligand, CD70, enhances proliferation and effector functions of NK cells. We used mice that constitutively express CD70 on B cells (CD70-Tg) to study the in vivo effects of continuous triggering of CD27 on NK cells. Continuous CD70-CD27 interaction resulted in strongly down-modulated CD27 expression on NK cells and gradually reduced absolute NK cell numbers. This reduction was most prominent in the mNK cell subpopulation and was at least partially due to increased apoptosis. Residual NK cells showed lower expression of activating Ly49 receptors and normal (liver) or decreased (spleen) IFN-gamma production. Nevertheless, NK cells from CD70-Tg mice displayed higher YAC-1 killing capacities. CD70-Tg NK cells exhibited up-regulated expression of NKG2D, which is in accordance with the increased YAC-1 lysis, as this is mainly NKG2D-dependent. Taken together, this study is the first to demonstrate that continuous CD70 triggering of CD27 on NK cells in vivo results in a severe reduction of NK cells. On a single cell basis, however, residual NK cells display enhanced cytotoxicity.

Chronic lymphocytic leukaemia cells drive the global CD4+ T cell repertoire towards a regulatory phenotype and leads to the accumulation of CD4+ forkhead box P3+ T cells.

Advanced chronic lymphocytic leukaemia (CLL) is associated with profound immunodeficiency, including changes in T regulatory cells (T(regs)). We determined the pattern of expression of forkhead box P3 (FoxP3), CD25, CD27 and CD127 and showed that the frequency of CD4+ FoxP3+ T cells was increased in CLL patients (12% versus 8% in controls). This increase was seen only in advanced disease, with selective expansion of FoxP3-expressing cells in the CD4+ CD25(low) population, whereas the number of CD4+ CD25(high) FoxP3+ cells was unchanged. CD4+ CD25(low) cells showed reduced expression of CD127 and increased CD27, and this regulatory phenotype was also seen on all CD4 T cells subsets in CLL patients, irrespective of CD25 or FoxP3 expression. Incubation of CD4+ T cells with primary CLL tumours led to a sixfold increase in the expression of FoxP3 in CD4+ CD25- T cells. Patients undergoing treatment with fludarabine demonstrated a transient increase in the percentage of CD4+ FoxP3+ T cells, but this reduced to normal levels post-treatment. This work demonstrates that patients with CLL exhibit a systemic T cell dysregulation leading to the accumulation of CD4+ FoxP3+ T cells. This appears to be driven by interaction with malignant cells, and increased understanding of the mechanisms that are involved could provide novel avenues for treatment.

Accumulation and activation of natural killer cells in local intraperitoneal HIV-1/MuLV infection results in early control of virus infected cells.

Natural killer (NK) cells are important effectors in resistance to viral infections. The role of NK cells in the acute response to human immunodeficiency virus 1 (HIV-1) infected cells was investigated in a mouse model based on a HIV-1/murine leukemia virus (MuLV) pseudovirus. Splenocytes infected with HIV-1/MuLV were injected intraperitoneally and local immunologic responses and persistence of infected cells were investigated. In vivo depletion with an anti-NK1.1 antibody showed that NK cells are important in resistance to virus infected cells. Moreover, NK cell frequency in the peritoneal cavity increased in response to infected cells and these NK cells had a more mature phenotype, as determined by CD27 and Mac-1 expression. Interestingly, after injection of HIV-1/MuLV infected cells, but not MuLV infected cells, peritoneal NK cells had an increased cytotoxic activity. In conclusion, NK cells play a role in the early control of HIV-1/MuLV infected cells in vivo.

Polymeric IgA-secreting and mucosal homing pre-plasma cells in normal human peripheral blood.

Clear identification of recently activated mucosal B cells in human blood would greatly facilitate study of mucosal vaccines, immune response to infection and the ongoing mucosal IgA response. We examined blood lymphocytes from normal, healthy individuals to identify IgA-secreting pre-plasma cells' (PPC) functional and phenotypic relevance to mucosal antibody production, in the absence of infection, disease or recent vaccination. PPC are the most recently activated B lymphocytes in blood and are considered in transit between lymphoid tissue and effector tissues, where they terminally differentiate into plasma cells. We observed that all IgA-secreting PPC expressed surface IgA (sIgA) and intracellular IgA (icIgA) and secreted primarily polymeric IgA (pIgA), as determined by flow cytometry, ELISPOT and size exclusion chromatography. A large sub-population of PPC in blood expresses the mucosal chemokine receptor CCR10 and contains the largest fraction of sIgA and icIgA PPC that secrete pIgA. The majority of CCR10(+) PPC expresses high levels of Ki67, indicative of recently activated blasts. In contrast, most CCR10(-) PPC secrete IgG, but a small population secretes pIgA and stains for icIgA. The mucosal integrin alpha(4)beta(7) was detected on a subset of PPC, but this subset did not account for all CCR10(+) PPC or all PPC with sIgA expression. Our data clearly demonstrate that PPC defined by surface expression of CD19, CD27(hi), IgA and CCR10 secrete only pIgA and are the dominant mucosal PPC subset in human blood. These mucosal PPC can now be investigated routinely as indicators of recent human mucosal IgA responses.

Resting human memory B cells are intrinsically programmed for enhanced survival and responsiveness to diverse stimuli compared to naive B cells.

Enhanced secondary Ab responses are a vital component of adaptive immunity, yet little is understood about the intrinsic and extrinsic regulators of naive and memory B cells that result in differences in their responses to Ag. Microarray analysis, together with surface and intracellular phenotyping, revealed that memory B cells have increased expression of members of the TNF receptor, SLAM (signaling lymphocytic activation molecule), B7, and Bcl2 families, as well as the TLR-related molecule CD180 (RP105). Accordingly, memory B cells exhibited enhanced survival, proliferation, and Ig secretion, and they entered division more rapidly than did naive B cells in response to both T cell-dependent and T cell-independent stimuli. Furthermore, both IgM and isotype-switched memory B cells, but not naive B cells, costimulated CD4+ T cells in vitro through a mechanism dependent on their constitutive expression of CD80 and CD86. This study demonstrates that up-regulation of genes involved in activation, costimulation, and survival provides memory B cells with a unique ability to produce enhanced immune responses and contributes to the maintenance of the memory B cell pool.