Activation of B cells by autoreactive T cells: cloned autoreactive T cells activate B cells by two distinct pathways

Although the existence of autoreactive T cells has been widely reported, the functional capacities of these populations have been less well defined. Studies were therefore carried out to characterize the relationship of autoreactive T cells to antigen-specific major histocompatibility complex (MHC)-restricted T cells in their ability to act as helper cells for the induction of immunoglobulin synthesis by B cells. A number of autoreactive T cell lines and clones were isolated from antigen-primed spleen and lymph node cell populations. Autoreactive T cells were found to proliferate in response to direct recognition of syngeneic I-A or I-E subregion-encoded antigens in the absence of any apparent foreign antigen. It was shown that cloned autoreactive T cells were capable of activating B cell responses through two distinct pathways. After appropriate stimulation by syngeneic cells, autoreactive T cells polyclonally activated primed or unprimed B cells to synthesize IgM antibodies. These activated T cells functioned in these responses through an MHC-unrestricted pathway in which polyclonal responses were induced in both syngeneic and allogeneic B cells. These cloned autoreactive T cells were also able to activate IgG responses by primed B cells through a different activation pathway. In contrast to the polyclonal activation of IgM responses, the induction of IgG antibodies by the same cloned T cells required primed B cells and stimulation with the priming antigen. The activation of B cells to produce IgG was strongly MHC restricted and required the direct recognition by the autoreactive T cells of self MHC determinants expressed on the B cell surface, with no bystander activation of allogeneic B cells. These results indicate that cloned autoreactive T cells resemble antigen-specific MHC-restricted T cells in their ability to function as T helper cells through distinct MHC-restricted and MHC-unrestricted pathways.     

Recognition of virus infected cells by NK cells

NK cells show cytotoxicity against virus-infected cells and tumor cells and play an important role in host defense. Although mecheanism of target cell recognition by NK cells have been unclear for a long time, it has recently been elucidated that certain NK cell receptors specifically recognize virus products. Furthermore, expression pattern of NK cell receptors, which consist of activating and inhibitory receptors, determines susceptibility to virus-infection. Here, we review recent progress of mechanism of recognition of virus-infected by NK cells.     

T cell proliferation induced by autologous non-T cells is a response to apoptotic cells processed by dendritic cells

Self-reactive T cells are present in the mature immune repertoire as demonstrated by T cell proliferation induced by autologous non-T cells in the autologous mixed lymphocyte reaction. This reaction generates regulatory T cells in vitro and may reflect immune regulatory pathways in vivo, but the antigenic peptides recognized remain uncharacterized. We revisited this issue in light of the importance of apoptosis in immune regulation. We found that apoptosis among peripheral blood non-T stimulator cells is associated with augmented induction of autologous T cell proliferation. Our data show that caspase activity in the non-T stimulator population is essential for induction of autologous T cell proliferation, suggesting that cellular components in the non-T cell fraction are enzymatically modified, most likely by effector caspases, and have a direct or indirect effect on autoreactive T cell activation. Furthermore, exposure of macrophage-derived dendritic cells to apoptotic non-T cells augments autologous T cell proliferation, and blockade of alpha(v)beta(5) integrin, but not alpha(v)beta(3), inhibits the capacity of irradiated non-T cells or dendritic cells to stimulate autologous T cell proliferation. These experiments, using an entirely autologous system, suggest the interpretation that autoreactive T cells may recognize self-Ags modified through the actions of caspases and presented to T cells by dendritic cells. Induction of an in vivo autologous mixed lymphocyte reaction by caspase-modified self-Ags present in apoptotic cells may represent a mechanism to maintain peripheral immune tolerance.     

Functional neuronal cells generated by human parthenogenetic stem cells

Parent of origin imprints on the genome have been implicated in the regulation of neural cell type differentiation. The ability of human parthenogenetic (PG) embryonic stem cells (hpESCs) to undergo neural lineage and cell type-specific differentiation is undefined. We determined the potential of hpESCs to differentiate into various neural subtypes. Concurrently, we examined DNA methylation and expression status of imprinted genes. Under culture conditions promoting neural differentiation, hpESC-derived neural stem cells (hpNSCs) gave rise to glia and neuron-like cells that expressed subtype-specific markers and generated action potentials. Analysis of imprinting in hpESCs and in hpNSCs revealed that maternal-specific gene expression patterns and imprinting marks were generally maintained in PG cells upon differentiation. Our results demonstrate that despite the lack of a paternal genome, hpESCs generate proliferating NSCs that are capable of differentiation into physiologically functional neuron-like cells and maintain allele-specific expression of imprinted genes. Thus, hpESCs can serve as a model to study the role of maternal and paternal genomes in neural development and to better understand imprinting-associated brain diseases.     

Targeting of human dendritic cells by autologous NK cells

NK cells have the capacity to spontaneously kill tumor cell lines, in particular cell lines of hemopoietic origin. In contrast, they do not generally kill nontransformed autologous cells. However, here we demonstrate that short-term activated polyclonal human NK cells, as well as human NK cell lines, efficiently lyse autologous dendritic cells (DC) derived from peripheral blood monocytes as well as Langerhans-like cells derived from CD34+ stem cells isolated from umbilical cord blood. Lysis of autologous DC by short-term activated NK cells and NK cell lines was dependent on granule exocytosis, since total abrogation of lysis was observed in the presence of EGTA. Induction of DC maturation by LPS, monocyte conditioned media (MCM), or stimulation through CD40 ligand (CD40L) rendered the DC less susceptible to lysis by NK cells. Infection of DC with influenza virus was likewise associated with a reduced susceptibility to lysis by NK cells. Thus, susceptibility to lysis by autologous NK cells is a particular property of immature DC. The present results are discussed in relation to the ability of DC to interact with NK cells and to the ability of NK cells to regulate development of specific immunity.     

Lysis of endothelial cells by autologous lymphokine-activated killer cells

The mechanisms of lysis of endothelial cells derived from human umbilical vein (HUVEC) by autologous lymphokine-activated killer (LAK) cells, generated from cord blood lymphocytes of the same donor, were investigated. Freshly isolated HUVEC as well as HUVEC cultured for several passages were efficiently lysed by autologous LAK cells, and their susceptibility to the LAK cells was almost the some as that of allogenic HUVEC. Complement-depletion experiments revealed that the lysis was mainly dependent on CD16-natural killer (NK) LAK cells. Pretreatment of HUVEC with recombinant interferon (rIFN) for 24 h made them resistant to lysis by autologous LAK cells, while pretreatment with either rIL-1. rTNF, or acidic or basic fibroblast growth factor did not alter the lytic sensitivity of HUVEC. The resistance of rIFN-treated HUVEC was specific to lysis by CD16⁺ NK LAK cells, and their lysis by CD3⁺ T-LAK cells was not significantly altered. Moreover, in comparison with control HUVEC or rIL-1-treated HUVEC, rIFN-treated HUVEC had a significantly less potent inhibitory effect on the lysis of untreated HUVEC, when used as an unlabeled target. This suggests that rIFN treatment may down-regulate the recognition of some molecules on HUVEC by rIL-2-activated NK cells. These data suggest that damage of the endothelium during LAK therapy is mainly dependent on LAK cells with a NK phenotype that can specifically recognize a certain molecule on autologous endothelial cells.     

Fructose production by immobilizedArthrobacter cells

Summary ImmobilizedArthrobacter cells (NRRL-B-3728) were used for continuous isomerization of glucose to fructose in a bioreactor system. The system utilized stationary phase (55h) cells (2.2×10⁹ CFU/ml saline) immobilized onto K-carrageenan (3% w/v) beads [cells were heated at 65°C for 10 min to inactivate endogenous proteolytic enzymes]. Immobilized-cell preparations were hardened using three different glutaraldehyde systems. Glutaraldehyde (0.2 M) treated-immobilized cells (pH 7.0, 5°C for 30 min) exhibited good gel strength and high glucose isomerase activities. Maximal bioreactor isomerization of 44% was achieved when a buffered feedstock containing 40% glucose was fed into the column (60°C) at a flow rate of 0.2 ml/min. The biological half-life of glucose isomerase activities in this system was 400 h. Scanning electron microscopy revealed large numbers of cells distributed within the beads. A thin layer surrounding the beads following glutaraldehyde treatment was mainly due to cross-linking reactions between cell proteins and glutaraldehyde. This layer prevented leaking of cells during continuous isomerization reaction.     

Immunoregulation by natural killer cells

Polyinosinic-polycytidilic acid (poly (I:C], a synthetic analog of viral double-stranded RNA (dsRNA), activates natural killer (NK) cells and inhibits induction or promotes termination of the primary IgM response in vivo. Suppression of responses was reproduced in vivo by interferons (IFN) which activate NK cells and in vitro by cells enriched for NK cells. The likelihood that NK cells may be involved in the normal regulation of IgM responses is supported by the following observations: immunization itself induces NK activity at times appropriate to account for termination, NK cells activated by immunization suppress in vitro, mice with high NK activity induced by immunization with one antigen have reduced responses to immunization with a second antigen, and mice with induced loss of NK activity fail to down-regulate IgM antibody responses normally.     

Forces exerted by locomoting cells

The movement of cells along substrata is a complex phenomenon involving cell extension and retraction, and cell-substratum adhesion. Knowledge is beginning to accumulate about the forces required for cell protrusion and retraction. Both of these processes also require traction to be exerted on the substratum, and new assays for these forces are under development. This review briefly discusses the forces that locomotory cells exert, in terms of both recent force measurements and possible mechanisms for their generation.     

Leukotriene synthesis by epithelial cells

Leukotrienes (LTs) are intercellular signaling molecules that evoke a variety of responses. They are best known as potent promoters of inflammation. Normally, LTs are produced primarily by leukocytes. As a result, current models regarding the production of LTs in the context of disease focus on the leukocytes as the site of production. Structural cells, including epithelial cells, are typically relegated to supportive roles. It is recognized that epithelial cells normally contain all the components necessary for LT synthesis except the enzyme 5-lipoxygenase (5-LO). There is accumulating evidence that some populations of epithelial cells normally express low levels of 5-LO and can synthesize LTs autonomously. Moreover, certain factors, including bacterial and viral infection, can promote the expression of 5-LO in airway, gastrointestinal and skin epithelial cells. The appearance of active 5-LO enzyme in epithelial cells at these sites may contribute to diseases like cancer, colitis and psoriasis. This paper reviews the state of our knowledge regarding the expression of 5-LO in epithelial cells, the factors that modify that expression, and the implications regarding pathogenesis.     

Vanadium uptake by yeast cells

During incubation with vanadyl, Saccharomyces cerevisiae yeast cells were able to accumulate millimolar concentrations of this divalent cation within an intracellular compartment. The intracellular vanadyl ions were bound to low molecular weight substances. This was indicated by the isotropic nature of the electron paramagnetic resonance (EPR) spectra of the respective samples. Accumulation of intracellular vanadyl was dependent on presence of glucose during incubation. It could be inhibited by various di- and trivalent metal cations. Of these cations lanthanum displayed the strongest inhibitory action. If yeast cells were exposed to more than 50 microM vanadyl sulfate at a pH higher than 4.0, a potassium loss into the medium was detected. The magnitude of this potassium loss suggests a damage of the plasma membrane caused by vanadyl. Upon addition of vanadate to yeast cells surface-bound vanadyl was detectable after several minutes by EPR. This could be the consequence of extracellular reduction of vanadate to vanadyl. The reduction was followed by a slow accumulation of intracellular vanadium, which could be inhibited by lanthanum or phosphate. Therefore, permeation of vanadyl into the cells can be assumed as one mechanism of vanadium accumulation by yeast during incubation with vanadate.