Biomedical subjects

Adam F Cunningham

Publications and source records attributed to Adam F Cunningham.

10 recordsLinked to original sources

PubMed2004

Homeostatic cell-cycle control by BLyS: Induction of cell-cycle entry but not G1/S transition in opposition to p18INK4c and p27Kip1.

Cell-cycle entry is critical for homeostatic control in physiologic response of higher organisms but is not well understood. The antibody response begins with induction of naive mature B cells, which are naturally arrested in G(0)/G(1) phase of the cell cycle, to enter the cell cycle in response to antigen and cytokine. BLyS (BAFF), a cytokine essential for mature B cell development and survival, is thought to act mainly by attenuation of apoptosis. Here, we show that BLyS alone induces cell-cycle entry and early G(1) cell-cycle progression, but not S-phase entry, in opposition to the cyclin-dependent kinase inhibitors p18(INK4c). Independent of its survival function, BLyS enhances the synthesis of cyclin D2, in part through activation of NF-kappaB, as well as CDK4 and retinoblastoma protein phosphorylation. By convergent activation of the same cell-cycle regulators in opposition to p18(INK4c), B cell receptor signaling induces cell-cycle entry and G(1) progression in synergy with BLyS, but also DNA replication. The failure of BLyS to induce S-phase cell-cycle entry lies in its inability to increase cyclin E and reduce p27(Kip1) expression. Antagonistic cell-cycle regulation by BLyS and p18(INK4c) is functionally linked to apoptotic control and conserved from B cell activation in vitro to antibody response in vivo, further indicating a physiologic role in homeostasis.

Animals↗

PubMed2004

Tubercle bacilli generate a novel cell wall-associated pigment after long-term anaerobic culture.

Many cases of tuberculosis result from reactivation of previously acquired latent infections. Models to study such persister forms often involve gradual depletion of oxygen during culture as poor aeration is a characteristic of non-progressive TB granulomas. Anaerobically cultured bacilli develop a thickened outer-most cell wall layer. Here, we analyzed this layer from anaerobically cultured Mycobacterium tuberculosis and Mycobacterium bovis BCG. By six weeks of anaerobiosis a pigment was detected at levels > 60-fold higher in anaerobic than aerobic bacilli. This pigment was responsible for the electron-dense appearance of the thickened cell wall layer and gave an electrospray mass spectrometry peak at 409 Da (M+Na)+ or (M+H)+. We termed this pigment APP1, anaerobically produced pigment 1, the first pigment identified in M. tuberculosis.

Anaerobiosis↗

PubMed2004

Pinpointing IL-4-independent acquisition and IL-4-influenced maintenance of Th2 activity by CD4 T cells.

Naive CD4 T cells develop Th2 activity early in primary responses to alum-precipitated proteins by producing IL-4 mRNA and inducing B cells to produce gamma1 and epsilon switch transcripts. Both IL-4-dependent and IL-4-independent pathways for IL-4 induction are recognized, but their relative contribution to the different phases of primary Th2 responses in vivo is uncertain. We show the primary induction of IL-4 synthesis in lymph nodes responding to alum-precipitated protein is overwhelmingly in antigen-specific CD4 T cells and is unimpaired in IL-4Ralpha(-/-) mice, which can produce but do not respond to IL-4 and IL-13. Ig class-switching in extra-follicular responses, reflecting Th2 activity, is also unimpaired in these mice. By contrast, 7 days after immunization--when T cells are selecting B cells in germinal centers and T cell priming has occurred--non-responsiveness to IL-4 is associated with smaller germinal centers, increased levels of T-bet and gamma2a switch transcripts and reduced gamma1 and epsilon transcripts. These data indicate that Th2 characteristics acquired during T cell priming and the initial CD4 T cell interaction with B cells are largely IL-4-independent, whereas IL-4 production induced during priming has a significant role in maintaining the Th2 phenotype as T cells select B cells in germinal centers.

Animals↗

PubMed2004

Responses to the soluble flagellar protein FliC are Th2, while those to FliC on Salmonella are Th1.

Features of the Th1 or Th2 phenotype start to develop during CD4 T cell priming. This study of the response to the bacterial flagellar protein FliC shows that either Th1 or Th2 responses can be induced in mice depending upon how FliC is presented. This is shown by assessing the cytokine mRNA and class of FliC-specific plasma cells induced in situ. Soluble recombinant (r)FliC and polymerized FliC are strongly Th2 polarizing, inducing IL-4, NIP45 and c-Maf mRNA as well as epsilon and gamma1 switch transcripts and switching to IgG1. CD28-requirement for this switching shows its T cell dependence. rFliC was unable to induce markers of Th1 activity including IL-12, T-bet and IFN-gamma. Conversely, when FliC is presented in its native context surface-bound on live, flagellated Salmonella, switching is predominantly to IgG2a (IgG2c in C57BL/6 mice), reflecting Th1 activity. The development of divergent FliC-specific polarization to either Th1 or Th2 indicates that the context in which this antigen is encountered rather than its intrinsic immunostimulatory properties determines the direction of Th polarization.

Adjuvants, Immunologic↗

PubMed2004

Loss of CD154 impairs the Th2 extrafollicular plasma cell response but not early T cell proliferation and interleukin-4 induction.

Ligation of CD40 by CD4 T cells through CD154 is key both to germinal centre induction and follicular T-dependent Ig class switching, but its requirement for aspects of T cell priming and extrafollicular antibody responses is less clear. Here comparison of the T helper (Th) type 2 response in lymph nodes from wild-type mice and CD154-deficient mice after immunization with alum-precipitated antigen reveals selective effects of this immunodeficiency. The timing and magnitude of the early interleukin (IL)-4 induction and proliferation in T cells of the T zone were unaltered by CD154 deficiency. As expected, germinal centres were not induced. Additionally the T-dependent extrafollicular antibody response, which initially requires T cell help but expands without further T cell involvement, was severely curtailed. The median number of extrafollicular antigen-specific plasma cells was 370-fold lower in CD154-deficient mice. Of these plasma cells the median proportion that had switched to IgG1 was <5%, while in wild-type mice the proportion was 89%. Surprisingly, some CD154-deficient lymph nodes showed substantial switching to IgG1. Commensurately, increases in gamma1 germline transcripts and Blimp-1 mRNA were observed, albeit significantly lower than in controls, but activation-induced cytidine deaminase mRNA was undetectable in CD154-deficient mice. These experiments demonstrate that the acquisition of some T cell priming characteristics can be CD154-independent; in contrast, T-dependent extrafollicular responses require CD154. Thus functional CD154 ligation during the first encounter of T cells and B cells in the T zone is critical for follicular and extrafollicular antibody responses.

Animals↗

PubMed2003

Characterization of human humoral responses to the major outer membrane protein and OMP2 of Chlamydophila pneumoniae.

Chlamydophila pneumoniae infection is associated with a range of diseases including pneumonia, asthma and heart disease. Although an obligate intracellular pathogen, high levels of antigen-specific antibody are induced and serology is frequently used to diagnose these infections. Proteins targeted by the humoral response include the major outer membrane protein (MOMP) and outer membrane protein 2 (OMP2). Using human anti-chlamydial sera we have defined the B cell epitopes recognized on MOMP and OMP2. Peptides from MOMP, unlike OMP2, were not strongly recognized. Two of these epitopes when linked to an inert carrier reacted strongly with high-titer anti-C. pneumoniae sera.

Antibodies, Bacterial↗

PubMed2003

Extrafollicular antibody responses.

In adaptive antibody responses, B cells are induced to grow either in follicles where they form germinal centers or in extrafollicular foci as plasmablasts. Extrafollicular growth typically occurs in the medullary cords of lymph nodes and in foci in the red pulp of the spleen. It is not a feature of secondary lymphoid tissue associated with the internal epithelia of the body. All types of naïve and memory B cells can be recruited into extrafollicular responses. These responses are associated with immunoglobulin class switching but, at the most, only low-level hypermutation.

Animals↗

PubMed2003

Rapid development of Th2 activity during T cell priming.

The paradigm of T helper-1 (Th-1) and Th-2 cells developing from non-committed naive precursors is firmly established. Th1 cells are characterized by IFNgamma production and, in mice, the selective switching to IgG2a. Conversely IL-4 production and selective switching to IgG1 and IgE characterize Th2 cells. Analysis of Th2 induction in vitro indicates that this polarization develops gradually in T cells activated by anti-CD3 in the presence of IL-4; conversely anti-CD3 and IFNgamma induce Th1 cells. In this report, we explore evidence that indicates that the T helper cell polarization in vivo cannot solely be explained by the cytokine environment. This is provided by studying the early acquisition of Th1 and Th2 activities during responses to a mixture of Th1 and Th2-inducing antigens. It is shown that these divergent forms of T cell help can rapidly develop in cells within a single lymph node. It is argued that early polarization to show Th-1 or Th-2 behavior can be induced by signals delivered during cognate interaction between virgin T cells and dendritic cells, in the absence of type 1 or type 2 cytokines. This contrasts with the critical role of the cytokines in reinforcing the Th-phenotype and selectively expanding T helper clones.

Adjuvants, Immunologic↗

PubMed2002

Th2 activities induced during virgin T cell priming in the absence of IL-4, IL-13, and B cells.

Virgin T cells being primed to Th2-inducing or Th1-inducing Ags, respectively, start to synthesize IL-4 or IFN-gamma as they begin to proliferate. Parallel respective induction of B cells to produce gamma1 or gamma2a switch transcripts provides additional evidence of early divergent Th activity. This report concerns the roles of IL-4, IL-13, and B cells in these early events in vivo. Th2 responses were induced in lymph nodes against hapten-protein given s.c. with killed Bordetella pertussis adjuvant. In T cell proliferation in wild-type mice, IL-4 message up-regulation and gamma1 and epsilon switch transcript production were underway 48-72 h after immunization. The absence of IL-4, IL-13, or B cells did not alter the early T cell proliferative response. The gamma1 and epsilon switch transcript production was still induced in the absence of IL-4, IL-13, or both, but at a reduced level, while the dominance of switching to IgG1 in the extrafollicular hapten-specific plasma cell response was retained. The up-regulation of IL-4 message was not reduced or delayed in the absence of B cells and was only marginally reduced by the absence of IL-13. It is concluded that signals delivered by dendritic cells, which are not dependent on the presence of IL-4, IL-13, or B cells, can prime virgin T cells and induce the early Th2 activities studied. These early events that direct virgin T cells toward Th2 differentiation contrast with the critical later role of Th2 cytokines in selectively expanding Th2 clones and driving further IL-4 synthesis.

Animals↗

PubMed2002

CDK inhibitor p18(INK4c) is required for the generation of functional plasma cells.

B cell terminal differentiation is associated with the onset of high-level antibody secretion and cell cycle arrest. Here the cyclin-dependent kinase (CDK) inhibitor p18(INK4c) is shown to be required within B cells for both terminating cell proliferation and differentiation of functional plasma cells. In its absence, B cells hyperproliferate in germinal centers and extrafollicular foci in response to T-dependent antigens but serum antibody titers are severely reduced, despite unimpaired germinal center formation, class switch recombination, variable region-directed hypermutation, and differentiation to antibody-containing plasmacytoid cells. The novel link between cell cycle control and plasma cell differentiation may, at least in part, relate to p18(INK4c) inhibition of CDK6. Cell cycle arrest mediated by p18(INK4C) is therefore requisite for the generation of functional plasma cells.

Animals↗