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S C Knight

Publications and source records attributed to S C Knight.

At least 19 recordsLinked to original sources
PubMed1992

Function of dendritic cells and changes in T cell proliferation in antigen-induced nonresponsiveness.

The ability of dendritic cells (DC) to acquire and present antigen to T cells during antigen-induced nonresponsiveness (AINR) in contact sensitivity was examined by studying cells from lymph nodes draining the sites of antigen challenge. Mice were pretreated on the right flank with either vehicle (AOO), oxazolone (Ox), or fluorescein isothiocyanate (FITC) and challenged 5, 10, or 20 days later with FITC on the left flank. At 5, 10, and 20 days, compared with animals pretreated with vehicle and challenged with FITC, those pretreated and challenged with FITC showed reduced acquisition of antigen by DC and the DC showed a reduced ability to stimulate naive T cells in vitro. Proliferation of T cells immediately on isolation (reflecting in vivo activity) was also reduced. When the time between pretreatment and challenge was extended to 40 days, the proliferative responses and antigen acquisition returned to normal. Animals sensitized with Ox and challenged with FITC showed nonspecific inhibition of T cell proliferation at 5 days only and not at later times and antigen levels on the DC from these animals were normal. The results show that low T cell proliferation during specific AINR in contact sensitivity may be a consequence of reduced acquisition and presentation of antigen by DC.

Animals↗
PubMed1992

Dendritic cells from patients with tropical spastic paraparesis are infected with HTLV-1 and stimulate autologous lymphocyte proliferation.

Dendritic cells (DC), important antigen-presenting cells for recruiting T cells into immune responses, are susceptible to infection with HIV-1 and this can cause either stimulatory or suppressive effects on T cells. We examined another human retrovirus, HTLV-1, to determine whether DC were infected and caused any changes in T-cell function. Patients infected with HTLV-1 who have tropical spastic paraparesis (TSP) show high 'spontaneous' lymphocyte proliferation. We studied the basis for this by analyzing the interactions in vitro between lymphocytes and antigen-presenting cells and compared cells taken from HTLV-1-positive TSP patients with those taken from HTLV-1-positive healthy carriers and HTLV-1-negative family members. In HTLV-1-positive individuals, 0.4-5.1% of the DC were infected with HTLV-1 as determined by in situ hybridisation. In TSP patients, depletion of DC and purification of T cells abolished 'spontaneous' lymphocyte proliferation. Reinstating the DC, but not B cells or macrophages, restored proliferation, an effect that was blocked by antibodies either to class II major histocompatibility antigens or to HTLV-1 itself. Thus, presentation of HTLV-1 antigens by infected DC to autologous T cells could result in the abnormal T-cell proliferation and cause the inflammatory reaction leading to tissue damage in TSP. We also speculate that persistent infection of DC with HTLV-1 and consequent continuous stimulation of T cells might be instrumental in the development of HTLV-1-mediated T-cell leukemia.

Dendritic Cells↗
PubMed1992

Development and function of dendritic cells in health and disease.

The life history of dendritic cells (DC) is now established from their origins from bone marrow stem cells, their distribution through blood to the tissues, and their movement via afferent lymph to lymph nodes for the initiation of immune responses. Bone-marrow stem cells, and occasional stem cells in peripheral blood (about 1 per 10(5) mononuclear cells), can give rise both to DC and macrophages (MO). In addition to stem cells in blood, after short-term culture of mononuclear cells, three major morphologic types of DC can be separated (types I-III), which probably represent the maturational pathway of this cell type; type II cells resemble tissue DC such as Langerhans cells and type III have a veiled morphology similar to that seen in cells of afferent lymph and in the interdigitating cells of the paracortex of lymph nodes. Functionally, DC cultured from peripheral blood are able to acquire large antigens and process them like Langerhans cells of the skin. They can also present antigens to stimulate primary T-cell responses, a property associated with lymph node DC. In tissues, DC appear to act as outposts of the immune system, acquire antigens, and, particularly in primary responses, carry the antigens to lymph nodes where they initiate T-cell responses. In secondary responses, activation of memory T cells in the periphery and the acquisition of antigen/antibody complexes by follicular dendritic cells of the lymph node follicles, which stimulate B cell memory, may be more important pathways for immune activation. DC may play a role in the development of many immunologic diseases including cancer, autoimmunity, and acquired immunodeficiency syndrome (AIDS).

Acquired Immunodeficiency Syndrome↗
PubMed1992

Oncogene expression in primary myelodysplasia: correlation with haematological, karyotypic, and clinical progression.

AIMS: To see if the relative expressions of proto-oncogenes that are increased in acute myeloid leukaemia are raised in patients with myelodysplastic syndromes (MDS), and to see if they increase with progression to leukaemia. To note if there is a correlation between morphology, karyotype, and these proto-oncogene expressions and if any one proto-oncogene can predict prognosis. METHOD: Bone marrow from 130 patients was analysed at six monthly intervals over two years for relative mRNA expression of seven oncogenes, karyotype, and morphology. The technique used slot blot hybridisation and densitometric analysis. The results were compared with 14 surgical controls and 30 people with vitamin deficiency anaemia. RESULTS: Six of seven oncogenes showed increased expression which progressed with time, but did not correlate with morphological or karyotypic changes. Expression of four of the seven oncogenes was increased in megaloblastic and iron deficiency anaemia. C-mos showed differences among the five morphological subgroups; it correlated with abnormal location (p = 0.025) and seemed to influence prognosis. CONCLUSION: Increased proto-oncogenes reflect the overall marrow perturbation in MDS. C-mos may reflect persistence of monocyte pathway which confirms marrow stability.

Aged↗
PubMed1992

Antigen-presentation by macrophages but not by dendritic cells in human immunodeficiency virus (HIV) infection.

Dendritic cells (DC) have a potent antigen-presenting capacity for recruiting resting T cells into immune responses. They also promote expansion of already activated memory T cells. By contrast, macrophages (M phi) are only effective in stimulating memory responses. Infection and depletion of DC occur in human immunodeficiency virus (HIV)-infected individuals and recruitment of T cells into primary responses is blocked. Here comparisons between DC and M phi in stimulating secondary T-cell responses in HIV infection were made. Adherent M phi, and DC isolated by a new method, were separated from peripheral blood of patients in different stages of HIV infection and from uninfected controls and added to allogeneic lymphocytes in mixed leucocyte reactions (MLR). Some were pulsed with influenza virus or tetanus toxoid and used to stimulate autologous T cells. Responses were measured from uptake of [3H]thymidine in 20 microliters hanging drop cultures. DC, but not M phi, from normal individuals stimulated MLR but both populations stimulated secondary responses to recall antigens. DC from all HIV seropositive individuals caused little or no stimulation of any lymphocyte responses. However, M phi from HIV seropositive asymptomatic individuals and those with persistent generalized lymphadenopathy stimulated responses to recall antigens. There was no stimulation using cells from acquired immune deficiency syndrome (AIDS) patients. Blocked DC but not M phi function may underlie progressive immunological non-responsiveness in HIV infection. Without recruitment of resting T cells, loss of memory T cells may be cumulative; failure of secondary activation (e.g. by M phi) would lead to lost T-cell activity. Identification and circumvention of the defect in DC could offer new therapeutic approaches.

Antigen-Presenting Cells↗
PubMed1991

Stimulatory and suppressive effects of infection of dendritic cells with HIV-1.

Two effects of HIV infection on human dendritic cells (DC) in vitro have been examined. The first was the stimulation of primary responses to HIV antigens in autologous lymphocytes from normal donors. When DC were exposed to HIV (10(4) TCID/10(5) cells) for up to 24 h before addition to autologous lymphocytes, a marked primary proliferative response to the virus was observed. No proliferative response was seen when the period of pre-exposure of DC to virus was extended. Cytotoxic T cells specific for HIV-infected target cells developed in stimulated cultures. The second effect of HIV infection of DC was to block responses to other antigens, such as alloantigens and the recall antigens tetanus toxoid and influenza virus. This inhibitory effect was only evident when the DC were exposed to HIV for longer than 24 h before being added to cultures. These in vitro studies suggest that infection of DC can produce both stimulatory and inhibitory responses in lymphocytes. Such effects operating through DC might underlie in vivo activity of HIV both in stimulating the proliferation of lymphocytes (e.g., in persistent generalised lymphadenopathy) and in the development of immunosuppression.

Dendritic Cells↗
PubMed1991

The distribution and functional properties of dendritic cells in patients with seronegative arthritis.

Dendritic cells (DC), potent antigen-presenting cells, are known to be increased in numbers in inflammatory lesions in rheumatoid arthritis and juvenile chronic arthritis. In this study, patients with seronegative arthritis were studied; the distribution and functional properties of DC enriched low density cells (LDC) from peripheral blood (PB) and synovial fluid (SF) were compared. The composition of LDC from both sources was similar, comprising approximately 30% DC, 60% monocytes with few T lymphocytes. SF was significantly enriched for LDC compared with paired peripheral blood (P less than 0.0001) or peripheral blood from healthy controls (P less than 0.001). In contrast, patient PB contained fewer LDC (P less than 0.05) overall than healthy controls. LDC from both sources were potent simulators of allogeneic PB T cells in a mixed leucocyte reaction (MLR), but in four out of 10 patients SF LDC were significantly more stimulatory. In autologous MLRs (AMLRs) SF T cells were not stimulated by either LDC population. This anergy of T cells was confined to the joint as patient PB T cells showed an AMLR response to PB LDC which was similar to that seen in cells from healthy controls. PB T cells also responded to SF LDC; in a minority of patients SF LDC caused significantly greater stimulation in AMLR than PB LDC and the possibility is discussed that this may represent presentation of antigen acquired in vivo.

Arthritis↗
PubMed1991

Peripheral blood and synovial fluid T cells differ in their response to alloantigens and recall antigens presented by dendritic cells.

Properties of T cells from inflammatory lesions were analysed by comparing the response of peripheral blood (PB) and synovial fluid (SF) T cells from 19 patients with a range of arthropathies to enriched allogeneic dendritic cells (DC) in a primary mixed leucocyte reaction (MLR). In 17 patients the proliferative response of SF T cells was significantly (P less than 0.05) less than that of PB lymphocytes. The reduced response of SF T cells was observed in all disease categories studied and could not be attributed to differences in cell number requirements or response kinetics. Addition of recombinant interleukin-2 enhanced the response of SF T cells in a dose-dependent manner. Cell mixing experiments suggested that active suppression was not the underlying mechanism of the poor MLR response of SF T cells. In contrast to the MLR response. SF T cells were able to mount vigorous proliferative responses to recall antigen presented by autologous antigen-presenting cells. The possibility is discussed that T cells compartmentalized at inflammatory lesions are a unique population with a diminished ability to interact with DC and respond to primary stimuli but an ability to respond to secondary antigenic challenge.

Arthritis↗
PubMed1991

Morphology and phenotype of dendritic cells from peripheral blood and their productive and non-productive infection with human immunodeficiency virus type 1.

Immununoelectron microscopy of human peripheral blood mononuclear cells enriched for the presence of antigen-presenting dendritic cells (DC) has revealed two morphologically distinct cell types both expressing DR and DQ major histocompatibility complex (MHC) class II antigens but lacking T, B, natural killer (NK) and monocyte/macrophage markers. The first (type 1) has an irregular surface with numerous projections and shows cytoplasmic vacuoles. The second (type 2) has a paler nucleus showing only a thin rim of dense heterochromatin, large expanses of cytoplasm devoid of organelles, fewer vacuoles and a smooth cell boundary with few processes. In addition a few cells with a morphology similar to veiled cells of the afferent lymphatics (type 3 DC) were observed. Cells with a morphology intermediate between these three types were observed, suggesting that they may represent stages of the veiled cell differentiation pathway. Type 2 and 3 DC were shown by electron microscopy to be susceptible to productive infection with human immunodeficiency virus (HIV), whilst type 1 DC did not support virus growth. Examination of infected DC preparations by in situ hybridization revealed a higher number of DC positive for viral DNA and RNA than for RNA alone. Thus, in addition to productively infected DC, there may be some that are latently infected, contain defective virus genome or replicate virus at a very low level.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Primary proliferative and cytotoxic T-cell responses to HIV induced in vitro by human dendritic cells.

In earlier studies, primary proliferative and cytotoxic T-cell (CTL) responses to influenza virus were produced in vitro by using mouse dendritic cells (DC) pulsed with virus or viral peptide as the stimulus for syngeneic T cells in 20-microliters hanging-drop cultures. We have now adapted this system for producing primary responses with cells from non-immune donors to produce primary proliferative and CTL responses to human immunodeficiency virus I (HIV) and to HIV peptides in vitro using cells from normal human peripheral blood. All donors in this study were laboratory personnel with no history of HIV infection. DC enriched from peripheral blood were exposed to HIV in vitro and small numbers were added to T lymphocytes in 20-microliters hanging drops. Proliferative responses to virus-infected DC were obtained after 3 days in culture. After 6 days, CTL were obtained that killed virus-infected autologous--but not allogeneic--phytohaemagglutinin (PHA)-stimulated blast cells. Proliferative and CTL responses were obtained using cells from 14 random donors expressing a spectrum of major histocompatibility complex (MHC) types but the CTL, once produced, showed killing restricted by the MHC class I type. Treatment of cultures with monoclonal antibody (mAb) to CD4-positive cells at the beginning of culture blocked the development of both proliferative and CTL responses, but treatment after 5 days had no effect on the CTL activity. Treatment with MCA to CD8-positive cells at the beginning of culture did not block proliferation significantly, but treatment either before or after the 5-day culture period blocked CTL responses. Collaboration between proliferating CD4-positive cells and CD8-positive cells may thus be required to produce CTL of the CD8 phenotype. DC exposed to HIV also produced CTL that killed autologous blast cells pulsed with gp120 envelope glycoprotein. However, DC infected with whole virus did not produce CTL that lysed target cells pulsed with a synthetic peptide, which included a known T-cell epitope of gp120 (representing amino acids 111-126). DC pulsed with gp120 were a poor stimulus for the development of CTL. In contrast, DC pulsed with the peptide (111-126) stimulated both proliferative and CTL responses. The latter killed not only target cells pulsed with the peptide itself or with gp120 but also killed virus-infected autologous blast cells. CTL were again obtained reproducibly with this peptide using donors expressing a spectrum of MHC types.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Division↗
PubMed1990

Identification of hematopoietic progenitors of macrophages and dendritic Langerhans cells (DL-CFU) in human bone marrow and peripheral blood.

Colonies of cells with distinctive dendritic appearance were observed in methylcellulose cultures of human bone marrow and peripheral blood mononuclear cells (PBMC). Such cells appeared alone in colonies of less than 50 cells, together with macrophages in mixed colonies and also within clusters of T lymphocytes at high culture cell numbers. The morphologic resemblance to lymphoid dendritic cells was confirmed by electron microscopy and the cells were distinguished from macrophages by immunoenzymatic and immunogold labeling with monoclonal antibodies (MoAbs). Like macrophages they were HLA-DR+ and CD4+. However, they lacked nonspecific esterase and the macrophage cytoplasmic marker Y1/82A. Most strikingly, cells were strongly HLA-DQ+ and expressed CD1a (T6), which is characteristic of skin Langerhans cells. Their functional similarity to lymphoid dendritic cells was demonstrated by their ability to stimulate allogeneic mixed leukocyte reactions. Dendritic cell colony numbers were estimated in both bone marrow and peripheral blood of controls and in leukemia and lymphoma patients before and after chemotherapy. Colony numbers were low in control blood and in patients before treatment (less than 1.0 to 3.7/10(5) cells). However, during hematopoietic recovery the mean value increased to 37.5/10(5) cells and this increase correlated closely with the observed increase in circulating colony forming unit-granulocyte macrophage (CFU-GM) in individual patients. Autoradiographic studies demonstrated mitotic activity within CD1a+ colonies and a linear relationship between cultured cells and both pure and mixed colonies was consistent with their derivation from a single precursor. These data indicate that a novel hematopoietic progenitor of dendritic/Langerhans cells (DL-CFU) may now be identified in a clonal assay system and suggest a probable common progenitor for these cells and macrophages.

Antibodies, Monoclonal↗
PubMed1990

The detection of human immunodeficiency virus DNA in dendritic cells from the joints of patients with aseptic arthritis.

Three patients with inflammatory arthritis were found to be seropositive for human immunodeficiency virus (HIV). Two of these individuals developed synovitis following an episode of yersinia bowel infection. We have studied joint material from all three in an attempt to define the role that HIV may be playing in the aetiology or maintenance of arthritis. Cell-associated HIV DNA was detected within joint fluid by in situ hybridization and the phenotypes of infected cells were established using a double-labelling immunocytochemical technique. Viral DNA was detected in dendritic cells (4-25%) isolated from both the peripheral blood and synovial fluid and in occasional lymphocytes from peripheral blood (less than 0.1%). No infected macrophages were seen. Functional studies using the mixed leucocyte reaction showed that the dendritic cells from synovial fluid were poor stimulators of allogenic peripheral blood lymphocytes whilst being effective at stimulating autologous lymphocytes. In addition, synovial fluid lymphocytes responded poorly to normal control dendritic cells. Infection of these cells with HIV could be contributing to this low stimulatory activity of antigen-presenting cells and to the unresponsiveness of lymphocytes.

Adult↗
PubMed1990

Low-dose immunosuppression by cyclosporine operating via antigen-presenting dendritic cells.

The inhibitory effect of cyclosporine on the stimulation of lymphocytes was tested in 20 microliters hanging drop cultures. Cells were stimulated by concanavalin A, or by allogeneic dendritic cells in a mixed leukocyte culture (MLC). Significant inhibition of lymphocyte proliferation was obtained with low concentrations of CsA (10(-9)-10(-7) micrograms/ml) in addition to the well-documented, dose-dependent inhibition at concentrations greater than or equal to 10(-1) micrograms/ml. Intermediate doses (10(-6)-10(-2) micrograms/ml) caused little inhibition. To establish whether the CsA was acting on the antigen-presenting cells or on the responding T cells, each population was pulsed with CsA before adding to the MLC. Higher doses of CsA were required to cause inhibition using this short-term pretreatment rather than continuous presence of CsA; however, when DC were pulsed with CsA, biphasic effects of the drug were seen. The time of DC pretreatment with 1 microgram/ml CsA was varied, and inhibition was seen after 1-3 hr and 16-24 hr pretreatment but not at intermediate time points. Similarly, a biphasic dose-response developed when DC-pretreatment time was fixed (2 hr) and drug concentration was varied. By contrast, on pulsing responder lymphocytes with CsA there was a biphasic effect in some experiments, but more often a single dose-dependent inhibition occurred, particularly when DC were removed from the responder cells. Major dose-dependent inhibitory effects of CsA may therefore act on both antigen-presenting DC and on lymphocytes, but this work reveals an additional low-dose inhibition that can operate via DC.

Animals↗
PubMed1990

HIV I infection of dendritic cells.

Dendritic cells (DC) from human peripheral blood are susceptible to productive and probably to latent infection with HIV-I. Infection of DC also occurs in vivo since in HIV-seropositive individuals Langerhans' cells of the skin and DC from peripheral blood, (in preparation) are infected. In peripheral blood 3-25% of DC, identified as large, low-density cells lacking monocyte markers, are infected as judged by in situ hybridization with an HIV probe. This contrasts with the lower proportion (< 0.2%) of other cells infected. DC exposed to HIV in vitro or in vivo fail to present other antigens or mitogens to stimulate T cells. This functional defect in infected DC is not blocked by the presence of soluble CD4 antigen and occurs in the absence of T cell infection suggesting a block at the level of the antigen-presenting cell itself. Infection, depletion and dysfunction of DC in HIV seropositive patients is already present in asymptomatic individuals and this precedes the appearance of T cell defects. We speculate that loss of functional DC may be a fundamental defect leading to a block in recruitment of resting T cells into immune responses. In contrast to the HIV-induced impairment of antigen presentation by DC, these cells were potent stimulators of responses to the HIV antigens themselves. Normal DC infected with HIV in vitro stimulated primary proliferative and cytotoxic T cell responses (in preparation). These were produced in cells from individuals expressing a range of different MHC types but the cytotoxic cells, once produced, killed autologous but not allogeneic, infected T cell blasts. Primary response to viral peptides can also be produced suggesting that this system may be useful for identifying immunogenic epitopes of HIV using cells from sero-negative, non-immunocompromised individuals.

CD4 Antigens↗
PubMed1990

Antigenic competition in contact sensitivity. Evidence for changes in dendritic cell migration and antigen handling.

The frequency and antigen-bearing characteristics of dendritic cells (DC) within draining lymph nodes have been examined during antigenic competition in contact sensitivity. Pre-exposure of mice to oxazolone on the flank resulted in a marked depression of subsequent fluorescein isothiocyanate (FITC)-induced lymph node cell (LNC) proliferation. Antigenic competition was associated with an increased frequency of DC in the draining lymph nodes, but also with a reduced amount of antigen per cell. Thus, at 24 hr the draining nodes of FITC-challenged mice previously exposed to oxazolone exhibited an increased number of DC compared with control animals. Flow cytometric analysis revealed, however, that the percentage of antigen-bearing DC was reduced and that the median amount of antigen borne by DC was lower. Since exposure to oxazolone caused a significant increase in the frequency of DC in distant nodes, the changes observed in antigenic competition may, at least in part, be attributable to systemic effects on DC migration following application of the first antigen. These data indicate that the reduced primary proliferative response which characterizes antigenic competition in contact sensitivity is associated with, and may result from, induced changes in dendritic cell behaviour.

Animals↗
PubMed1990

Systemic migration of dendritic cells during contact sensitization.

Twenty-four hours after skin painting mice on the flank with the contact sensitizer fluorescein isothiocyanate (FITC), the number of dendritic cells (DC) increased sharply, not only in draining but also in contralateral (CLN) and distant lymph nodes. High levels of antigen were detected on up to 50% of DC isolated from draining lymph nodes (DLN), and these cells were potent stimulators of naive T cells in vitro. Less than 3% of DC from contralateral and distant lymph nodes carried detectable antigen and did not induce significant T-cell proliferation. A significant number of DC had migrated to draining, contralateral and distant lymph nodes without acquiring detectable antigen. This indicates that there is a systemic signal causing the movement of DC to lymph nodes. This appears to be independent of mature T cells, as the systemic migration of DC also occurred in nude mice.

Animals↗