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Biomedical subjects

S C Knight

Publications and source records attributed to S C Knight.

At least 73 records · Page 4Linked to original sources
PubMed1995

A peptide of Chlamydia trachomatis shown to be a primary T-cell epitope in vitro induces cell-mediated immunity in vivo.

Chlamydiae are a major cause of infertility and preventable blindness and there is currently no effective vaccine in humans or rodents against these organisms. We have previously shown that a peptide of 12 amino acids (termed TINKP) from a conserved region of the major outer membrane protein (MOMP) of Chlamydia trachomatis (C. trachomatis) is a primary T-cell epitope in humans. Here we showed that when dendritic cells (DC) from C3H or BALB/c mice were pulsed in vitro with the peptide they stimulated proliferation of syngeneic T cells in vitro indicating that the peptide is also a primary T-cell epitope in mice. Since the skin is a rich source of DC, we immunized mice from each strain with an intradermal injection of the peptide. Humoral and cell-mediated immunity to peptide, MOMP or whole elementary bodies (EB) of C. trachomatis (F/NI1/GU) were assessed. No antibody response to TINKP was observed. However, immunized mice showed recall responses to all three chlamydial antigens. T-cell-mediated immunity in the absence of antibody was induced by a single injection of the peptide intradermally. C. trachomatis isolated from the human genital tract causes salpingitis in mice. Preliminary studies in susceptible C3H mice indicated that intradermal injection of peptide conferred some protection against the development of salpingitis. Thus, a primary T-cell epitope identified by in vitro stimulation using DC can also initiate cell-mediated immunity in vivo and this approach may be useful in the development of vaccines.

Animals↗
PubMed1994

AIDS. A problem of antigen presentation?

Evidence is accumulating that antigen-presenting dendritic cells--both those that activate T cells and those that interact with B cells--may be involved in the development of immunodeficiency during HIV-1 infection.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Murine retrovirus induces defects in the function of dendritic cells at early stages of infection.

The infection and function of lymph node dendritic cells (DC) were analyzed at different time points of Rauscher leukemia virus infection in mice (3, 7, 14, and 21 days). Infection of DC was apparent after 3 days and significant infection (1-10% of the DC population) was documented after 7 days. DC from infected mice as early as 3 days postinfection had a reduced ability to stimulate allogeneic normal T cells in the mixed lymphocyte reaction. T cells did become infected during the coculture but block of cross-infection of T cells by zidovudine did not abolish the inhibitory effect. Other DC-dependent responses were also reduced on infection including DC-stimulated responses to influenza virus. ConA and PMA induced an increase in [Ca2+]i level in DC from control mice. A low baseline level of [Ca2+]i in DC from infected mice and reduced calcium mobilization upon ConA stimulation was found at all periods of infection. Ultraviolet-inactivated Rauscher leukemia virus failed to provoke significant changes in DC function in vivo. Six or 7 days after RLV infection DC expressed lower levels of Iad but not H2Dd molecules in parallel with lower expression of some adhesion molecules (CD18, CD54, CD44). No differences in expression of B7 surface antigen between control and infected mice were obtained. We did not find any evidence for the induction of apoptosis of naive syngeneic or allogeneic T cells by infected dendritic cells. The changes in DC function may have implications for the pathogenesis of retroviral infections including HIV infection.

Animals↗
PubMed1994

Dendritic cells from HIV-1 infected individuals show reduced capacity to stimulate autologous T-cell proliferation.

Dendritic cells (DC) exposed for a short period of time (1 day) in vitro to HIV infection caused stimulation of autologous T-cells, but those exposed for a longer period (3 days) before addition to T-cells stimulate little or no proliferation [1]. Since a proportion of DC from patients who are HIV-1 seropositive is infected with HIV-1 [2] we used the same culture system to test the level of ongoing stimulation of autologous T-cells by DC. The DC from patients with HIV-1 infection showed no enhanced stimulation of autologous T-cells; they produced significantly lower levels of proliferation than those induced by DC from normal controls or from high risk seronegative individuals. However, DC stimulated production of antibodies to gp120 and p24 in cultures containing autologous B plus T-cell in the absence of any added exogenous antigens as previously described [3]. DC in asymptomatic individuals thus appear to be fuelling antibody production but not T-cell proliferation. The results suggest that a failure by DC to stimulate T-cell proliferation either to HIV-1 or to other environmental antigens may be involved in the failure of cell-mediated responses in HIV infection.

Cells, Cultured↗
PubMed1994

Dendritic cells persistently stimulate antibody responses to HIV in seropositive individuals.

OBJECTIVES: B-cell hyperactivity and hypergammaglobulinaemia with high levels of HIV-1-specific antibody occur during HIV-1 infection. We investigated the role played by antigen-presenting cells (APC) in the ongoing production of antibody. METHODS: Adherent monocytes and non-adherent low density dendritic cells were enriched from peripheral blood of patients at different stages of HIV-1 infection (Centers for Disease Control and Prevention categories II, III and IV) and from control subjects at high or low risk of HIV infection. Different concentrations of lymphocytes were cultured in 20 ml hanging drops in the presence or absence of autologous dendritic cells or monocytes. Antibodies to p24 and gp120 were assessed by enzyme-linked immunosorbent assay. RESULTS: Lymphocytes taken from asymptomatic HIV-1-seropositive subjects and depleted of APC produced low or moderate levels of antibody to gp120 or p24 in vitro. However, adding back autologous dendritic cells significantly enhanced antibody production, although fewer samples showed responses to p24 than to gp120. Less antibody production was stimulated using cells from patients with persistent generalized lymphadenopathy, or if monocytes rather than dendritic cells were added back. Little or no antibody was produced by cells from patients with AIDS and no antibody was detected in cultures of cells from seronegative individuals with low or high risk for infection. CONCLUSIONS: The evidence suggests that ongoing humoral responses to HIV-1 are fuelled by dendritic cells. Thus, the dominance of humoral over cell-mediated responses in HIV-1 infection may depend upon signalling via dendritic cells. Changes in signalling by dendritic cells could be central to the immunologic features of HIV-1 infection.

Antibody Formation↗
PubMed1994

Failure in antigen responses by T cells from patients with common variable immunodeficiency (CVID).

Antigen-driven responses by T cells from patients with CVID and normal subjects have been assessed. Low-density cells enriched for antigen-presenting dendritic cells were cultured with T cells using a 20-microliters hanging drop system. T cells from all subgroups of CVID patients showed markedly reduced responses to the recall antigens purified protein derivative (PPD) or tetanus toxoid, whereas responses by cells from patients with X-linked agammaglobulinaemia, used as a disease control, were in the normal range. However, primary allo-stimulation of CVID T cells was normal. CVID cells from two patients failed to respond to stimulation with a neoantigen, an HIV env peptide, under conditions where normal T cells did respond. These data illustrate a profound defect in antigen-stimulated T cell proliferation in vitro in all groups of CVID patients, but do not distinguish whether the defect is in the presenting cell or in the T lymphocyte. In vivo, germinal centre B cells are thought to present antigen to primed T cells to obtain essential signals (e.g. CD40 ligand and IL-2) for B cell survival and progression to immunoglobulin secretion. A failure of antigen-specific T cell function in vivo in CVID would thus not provide the primed T cells needed for B cell rescue, and could be the primary defect leading to the low immunoglobulin production in this condition.

Antigen-Presenting Cells↗
PubMed1994

Differential function of dendritic cells isolated from blood and lymph nodes.

Dendritic cells (DC) isolated from the lymph nodes or spleens of mice and pulsed with contact sensitizers or protein antigens stimulate primary proliferative responses by syngeneic T cells and responses to alloantigens in the mixed leucocyte reaction (MLR). Using enriched human peripheral blood DC, we attempted to stimulate primary immune responses to contact sensitizers by autologous lymphocytes in vitro. No significant proliferation above background levels or CD69 expression (an early activation antigen on lymphocytes) was detected despite using a wide range of donors, chemicals, antigens and cell concentrations. Culture of DC for up to 5 days in vitro in the presence of phytohaemagglutinin (PHA)-conditioned culture supernatants, or recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) also failed to induce primary proliferative responses to contact sensitizers. Comparisons were made between blood and lymph node DC from mice to explore whether the lack of stimulation was the result of differences between mouse and human DC or between DC isolated from different tissues. DC from lymph nodes stimulated primary responses to contact sensitizers in both blood and lymph node lymphocytes whereas blood DC did not stimulate responses. Both lymph node and blood DC stimulated an allogeneic MLR, although blood DC were less efficient than those from lymph node. The data show that DC from different tissues exhibit variable functional activity. DC from blood and lymph nodes were examined to determine whether surface antigen expression is related to functional activity. Murine blood DC expressed similar levels of LFA-1, LECAM-1 and CD44 compared with lymph node DC but lower levels of MHC class II, B7 and ICAM-1. These results may therefore have important implications for antigen processing and presentation in cells from different tissue compartments.

Allergens↗
PubMed1994

Dendritic cells are potent antigen-presenting cells for in vitro induction of primary human CD4+ T-cell lines specific for HIV gp120.

Activation of T helper cells specific for viral antigens is critical for antibody production and for generation of cytotoxic cells during the immune response to HIV. Since T-cell activation depends on antigen-presenting cells (APCs), it is important to define the cells that have a role in presentation of HIV antigens in general and of gp120 in particular. Peripheral blood mononuclear cells (PBMCs), adherent monocytes (AMs), dendritic cells (DCs) and Epstein Barr virus-transformed B-cell lines (LCLs) were tested for the capacity to present gp120 to a specific T-cell clone. DCs proved to be the most effective APC. Primary T-cell lines were generated from uninfected and unprimed individuals by using different APCs in the presence of gp120 or an immunodominant peptide. T-cell lines specific for gp120 were obtained with PBMCs or DCs as APCs, but not with AMs or LCLs. The data showed that (a) DCs are the most effective APCs for presentation of gp120 to specific T cells and (b) DCs are necessary for in vitro induction of primary T-cell lines specific for gp120.

Antigen Presentation↗
PubMed1994

Retrovirus-induced immunosuppression via blocking of dendritic cell migration and down-regulation of adhesion molecules.

Dendritic cells (DC) within tissues may acquire and process antigens, carry them into lymph nodes and cluster and activate T cells. The ability of DC to acquire antigen and to migrate to lymph nodes was estimated during murine retroviral infection caused by Rauscher leukaemia virus (RLV). A novel mechanism of inducing immunodeficiency has now been identified. In mice infected with RLV, DC failed to migrate into lymph nodes following exposure of the skin to the contact sensitizer, fluorescein isothiocyanate. RLV infection of a proportion of DC both in skin and lymph nodes, shown by semi-quantitative polymerase chain reaction (PCR) and down-regulation of expression of adhesion molecules (CD54 and CD44) on the surface of Langerhans' cells, may contribute to the described phenomenon. A failure of DC migration could be an important immunosuppressive mechanism of RLV infection in mice and we speculate on a similar role for DC in human immunodeficiency virus-1 (HIV-1) infection in humans.

Animals↗
PubMed1993

Differential effect of IL-10 on dendritic cell-induced T cell proliferation and IFN-gamma production.

IL-10 has previously been shown to inhibit cytokine production by Th1 cells by blocking macrophage accessory cell function. In this study we demonstrate that dendritic cell-induced Th1 proliferation was unaffected by IL-10, whereas macrophage-stimulated proliferation was inhibited in the same system. In contrast dendritic cell induced IFN-gamma production by the Th1 clones was down-regulated by IL-10. Inasmuch as dendritic cells have been shown to be potent APC for T cells in primary responses we determined the effect of IL-10 on dendritic cell-induced proliferation and IFN-gamma production by CD4+ and CD8+ T cells. Dendritic cells were effective at stimulating both proliferation and IFN-gamma secretion of CD4+ or CD8+ T cells in a primary allogeneic mixed leukocyte response. In contrast, IL-10 markedly inhibited dendritic cell driven IFN-gamma production by purified CD4+ and CD8+ T cells. Down-regulation of dendritic cell-induced IFN-gamma production suggests a role for IL-10 in inhibiting the initiation of cell-mediated immune responses.

Animals↗
PubMed1993

Effects of murine leukemia viruses on the function of dendritic cells.

In asymptomatic human immunodeficiency virus-1 infection T cells respond normally to allogeneic dendritic cells (DC), but DC show reduced stimulatory capacity. By contrast in HTLV-1 infection no significant changes in allogeneic stimulation were seen but DC-stimulated activity of autologous T cells. In seeking animal models relevant to these diseases the effects of two murine leukemia retroviruses, Rauscher leukemia virus (RLV) and Moloney leukemia virus (MLV) on the function of dendritic cells and T cells in a primary mixed leucocyte reaction have been tested. Treatment by RLV in vitro suppressed the ability of DC to stimulate allogeneic T cells from healthy animals. MLV at the same concentration did not significantly affect the ability of DC to stimulate allogeneic T cells, but provoked considerable enhancement of the low level stimulation by DC in the syngeneic system. Similar results were obtained following in vivo exposure to viruses. Two pieces of evidence suggested that these effects were due to impairment of DC function and were not operating through infection of T cells. Firstly, exposure of T cells directly to virus in vitro and in vivo before stimulation with untreated allogeneic DC caused no significant alteration in T cell activity. Secondly, the impact of murine leukemia virus on DC function was not abrogated when infected DC were added to normal T cells and cultured in the presence of zidovudine. Treatment of DC by RLV caused a decrease of cluster formation with allogeneic T cells. No statistically significant influence of MLV was observed on cluster formation after 3-h of incubation in the allogeneic system. However, after 18-h incubation MLV-treated DC formed fewer clusters with T cells than untreated DC. At the same time a stimulatory effect of MLV on DC cluster formation with syngeneic T cells was found. Considerable decrease was found in major histocompatibility complex class II antigen and LFA-1 receptor expression on the DC surface in mice infected by RLV. MLV induced no significant changes. These mouse retroviruses can therefore cause changes in DC function similar to those already reported using human retroviruses and may provide models for studying their effects.

Animals↗
PubMed1993

Dendritic cells in HIV-1 and HTLV-1 infection.

Individuals with HIV-1 infection show two major immunological effects--the early persistent stimulation of immune responses (e.g. of CD8 cells and antibody production) and later catastrophic immunodeficiency. Peripheral blood dendritic cells (DC) become infected with HIV-1 and infected cells can stimulate responses to virus. By contrast infected DC show a reduced capacity to stimulate either primary or secondary responses to other antigens. We have proposed that the block, particularly in primary responses, may be instrumental in the development of immunodeficiency. In HTLV-1 infected patients with tropical spastic paraparesis (TSP) a major feature of disease is 'spontaneous' T cell proliferation thought to underlie development of inflammatory neurological disease. We have now shown that some DC in addition to T cells are infected in TSP and that DC stimulate the persistent T cell activity. Here we demonstrate this using cells from an informative family where the daughter was normal, the father an HTLV-1 seronegative carrier and the mother had TSP. DC from all individuals stimulated normal allogeneic T cells in a mixed leukocyte reaction (MLR) and T cells responded well to normal allogeneic DC. T cells from the daughter showed little stimulation with autologous DC, those from the father showed significant but low stimulation, and T cells from the TSP patient gave a response to autologous DC which exceeded that to allogeneic DC. Taken together, the studies of DC and both HIV-1 and HTLV-1 indicate that infection of DC may play a central role in development of T cell abnormalities in human retrovirus-induced diseases.

Carrier State↗
PubMed1993

Antigen-presenting cell types.

Different antigen-presenting cells elicit responses in different T-cell populations for primary activation, secondary stimulation and cytotoxic effector functions. Maturing bone marrow derived dendritic cells may acquire and process antigens, transport them to lymph nodes and activate naive T cells located there. By contrast, follicular dendritic cells, acquiring antigen-antibody complexes, maintain 'memory' via B-cell activation. Effector memory T cells recognize various tissue cells bearing antigen and we speculate that they may also target specialized antigen-presenting dendritic populations.

Animals↗