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M Sileghem

Publications and source records attributed to M Sileghem.

32 records · Page 2Linked to original sources
PubMed1992

Detection and neutralization of bovine tumor necrosis factor by a monoclonal antibody.

Monoclonal antibodies (MAbs) have been produced which are specific for bovine tumor necrosis factor (TNF). MAb BC9 detects bovine TNF in a radioimmunoassay with a detection limit of 24 pg/ml. BC9 also neutralizes the in vitro biological function of bovine recombinant TNF. The activity of 250 ng TNF/ml was entirely neutralized by 1% ascitic fluid. When ascites was added at a saturating concentration (10% ascitic fluid), up to 25 micrograms TNF per ml was neutralized. The neutralizing effect of BC9 was seen in cytotoxic assays using L929 cells and WEHI 164 clone 13 cells. The cytotoxic activity of supernatants from in vitro activated bovine monocytes was entirely blocked by BC9.

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PubMed1992

Suppression of T-cell responsiveness during tsetse-transmitted trypanosomiasis in cattle.

In the present study, we demonstrate that lymph node cells from cattle infected with T. congolense through tsetse fly challenge were unable to proliferate in vitro following activation with the T-cell mitogen Concanavalin A. This was associated with a simultaneous suppression of interleukin 2 (IL-2) production and interleukin 2 receptor (IL-2R) expression. However, the capacity of the cells to secrete interferon gamma following the mitogenic activation was not affected by the infection.

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PubMed1992

Parasite-specific T-cell responses of trypanotolerant and trypanosusceptible cattle during infection with Trypanosoma congolense.

During primary tsetse-transmitted challenge of Boran (Bos indicus) cattle with Trypanosoma congolense ILNat 3.1, a transient parasite antigen-specific T-cell proliferative response was observed in peripheral blood mononuclear cells and splenic mononuclear cells stimulated in vitro. A response was also observed with cells of N'Dama (Bos taurus) cattle, but in this case higher stimulation indices were observed and the response was maintained until the termination of the experiment at 40 days post-infection (p.i.). The highest parasite antigen-specific proliferative responses were observed at 20 days post-infection. At this time N'Dama cattle not only responded to the antigens derived from the infecting clone (ILNat 3.1), but also to antigens from a clone of a different serodeme (ILNaR 2), whereas Boran cattle only recognized antigens from the infecting clone of parasites. To determine the molecular mass of the antigenic trypanosome proteins, whole trypanosome lysates made from T. congolense ILNat 3.1 were fractionated by SDS-PAGE and transferred onto nitrocellulose membranes. The major protein bands were isolated and used directly in T-cell proliferation assays. In this instance, no differences in the antigen recognition profiles of Boran and N'Dama cattle were observed. The variable surface glycoprotein did not induce T-cell proliferation in infected cattle despite the presence of serum antibodies to this variable antigenic type.

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PubMed1992

Mechanisms underlying trypanosome-elicited immunosuppression.

T-cell proliferative responses of lymph node cells are profoundly suppressed during experimental infections of mice with Trypanosoma brucei. The active suppression of lymph node T-cell proliferative responses is attributed to the coexistence of at least two unlinked suppressive mechanisms that block different T-cell regulatory steps and operate through different effector mechanisms. The generation of prostaglandin-producing macrophages is entirely responsible for the suppression of IL-2 production whereas the induction of a prostaglandin-independent suppressive mechanism accounts for the suppression of the expression of IL-2 receptors (IL-2R). Both mechanisms are mediated by the cells that co-purify which macrophages. Despite an impairment at the level of T-cell proliferation, lymph node cells from T. brucei infected animals produce substantial amounts of interferon-gamma (IFN-gamma) and this lymphokine participates in the down-regulation of IL-2R expression. T-brucei-pulsed macrophage cell lines acquire concomitantly the potential to suppress T-cell proliferative responses and to stimulate CD8+ T-cells to secrete IFN-gamma. The sensibilization of CD8+ T cells by T. brucei-pulsed macrophages might be mediated by TNF-alpha. Collectively, these results indicate that the uptake of T. brucei by macrophages, either in vivo or in vitro, results in the generation of suppressive cells that annihilate T-cell proliferative responses. Furthermore, at least two cytokines (i.e., TNF-alpha and IFN-gamma) are released during these interactions. Besides playing a role in the pathway of T-cell immunosuppression, TNF-alpha and IFN-gamma could also contribute to immunopathological features that occur during trypanosome infections.

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PubMed1992

Selection of BoCD25 monoclonal antibodies by screening mouse L cells transfected with the bovine p55-interleukin-2 (IL-2) receptor gene.

The bovine interleukin-2 receptor-alpha (IL-2R alpha) gene has been isolated and a rabbit antiserum against a fusion protein of the gene has been produced. However, the antiserum does not inhibit IL-2-dependent proliferation. Since a panel of monoclonal antibodies (mAb) to bovine activation antigens was available, we transfected the gene into mouse L fibroblasts, selected stable transfectants with the rabbit antiserum, and screened for antibodies that bound the transfected cells but not the untransfected cells. Three mAb were selected and all three precipitated a molecule of M(r) 55,000 (under reducing conditions) from activated cells, as expected from homology with mouse and human IL-2R alpha (CD25, Tac). One of the three mAb was a strong inhibitor of IL-2-dependent proliferation of bovine lymphocytes. Thus, the availability of transfected cells allowed us to establish quickly and unequivocally the antigenic specificity of a number of antibodies.

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PubMed1991

The role of the macrophage in induction of immunosuppression in Trypanosoma congolense-infected cattle.

Impairment of T-cell function in Boran (Bos indicus) cattle during primary infection with Trypanosoma congolense ILNat 3.1 was found to occur in peripheral blood, spleen and, in particular, the lymph nodes. Lymph node cells from infected cattle failed to proliferate in response to mitogenic stimulus and suppressed proliferation of both normal peripheral blood mononuclear cells and lymph node cells in co-culture assays. The addition of indomethacin, to inhibit prostaglandin synthesis, had no effect on the ability of lymph node cells from infected cattle to suppress the proliferative response of responder cells from uninfected cattle. The supplementation of the culture media with catalase, which degrades hydrogen peroxide, either alone or in combination with indomethacin, also did not result in restoration of proliferation. This suggested the presence of suppressor cells in lymph nodes of infected cattle which exert their effects via a prostaglandin-independent mechanism. By depleting lymph node cells from infected cattle of the monocyte-macrophage population using a cell sorter it was possible to abrogate the previously observed immunosuppression, thus indicating a key role for these macrophages in the induction of trypanosome-associated immunosuppression.

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PubMed1991

In vitro simulation of immunosuppression caused by Trypanosoma brucei.

Macrophage populations derived from Trypanosoma brucei-infected mice suppress both interleukin-2 (IL-2) production and IL-2 receptor (IL-2R) expression. A prostaglandin-independent mechanism accounts for the suppression of IL-2R expression, while the suppression of IL-2 is prostaglandin-dependent. A macrophage hybridoma cell line (i.e. 2C11-12) was used to mimic the parasite-induced immunosuppression in vitro. It was found that 2C11-12 cells acquired a suppressive potential in vitro following interaction with opsonized living parasites. T. brucei-pulsed 2C11-12 cells failed to block IL-2 secretion in the presence of indomethacin but still suppressed the IL-2R expression. In contrast, addition of living T. brucei parasites to the cultures caused a complete suppression of IL-2 secretion and IL-2R expression, even in the presence of indomethacin. Hence, the addition of excess living parasites to the cultures could cause a depression which was different from the suppression associated with infection, whereas the addition of parasite-pulsed 2C11-12 cells mimicked the situation occurring during infection. This model system can be adopted as a suitable tool to unravel the mechanisms underlying the suppression of IL-2R expression during T. brucei infections.

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PubMed1989

Different mechanisms account for the suppression of interleukin 2 production and the suppression of interleukin 2 receptor expression in Trypanosoma brucei-infected mice.

Lymph node cell populations derived from Trypanosoma brucei-infected mice failed to produce interleukin 2 (IL 2) in response to a potent mitogenic trigger and suppress the potential of normal lymph node cells to secrete IL 2 in co-culture assays. This suppression is promptly restored by the addition of indomethacin, which blocks prostaglandin synthesis, but is not markedly affected by the addition of catalase, which degrades H2O2. The suppression of the IL 2 receptor expression, on the other hand, is not restored by the addition of indomethacin, nor by the simultaneous supply of both indomethacin and catalase. This discrepancy is not caused by an extreme susceptibility of the receptor expression to low prostaglandin (PG) concentrations, but rather by the presence of suppressive cells that operate through a PG-independent mechanism. This suppressive mechanism accounts for the loss of the IL 2 receptors on both the Ly-2+ and the L3T4+ T cell compartment. The indomethacin-treated co-cultures, which manifest a normal IL 2 production but lack the IL 2 receptors, manifest an impaired DNA synthesis and contain a decreased number of T cell blasts.

Animals↗
PubMed1989

Dual role of macrophages in the suppression of interleukin 2 production and interleukin 2 receptor expression in trypanosome-infected mice.

Lymph node cells derived from T. brucei-infected mice fail to produce interleukin 2-(IL2) subsequent to a potent mitogenic trigger and actively suppress the capacity of normal cells to produce IL2 in co-culture experiments. The depletion of Thy-1+ cells does not decrease but rather increases the suppressive potential of the LNC derived from infected mice. A T cell-enriched nylon wool-nonadherent fraction, on the other hand, is not suppressive. The suppression of IL2 production is promptly restored by the addition of prostaglandin synthesis inhibitors suggesting a key role of the prostaglandin-producing macrophages. Our data indicate that such macrophages do not act indirectly through the induction of suppressor T cells, but rather directly interfere with the normal lymph node cells. In contrast to the essential role of prostaglandins in the impairment of IL2 production, these mediators are not involved in the suppression of IL2 receptor expression. Lymph node cells derived from Trypanosoma brucei-infected mice fail to produce interleukin 2 (IL2) subsequent to a potent mitogenic trigger and actively suppress the capacity of normal cells to produce IL2 in co-culture experiments. The depletion of Thy-1+ cells does not decrease but rather increases the suppressive potential of the LNC derived from infected mice. A T cell-enriched nylon wool-nonadherent fraction, on the other hand, is not suppressive. The suppression of IL2 production is promptly restored by the addition of prostaglandin synthesis inhibitors suggesting a key role of the prostaglandin-producing macrophages. Our data indicate that such macrophages do not act indirectly through the induction of suppressor T cells, but rather interfere directly with the normal lymph node cells.

Animals↗
PubMed1989

Modulation of IL-1 production and IL-1 release during experimental trypanosome infections.

Macrophage populations derived from Trypanosoma brucei-infected mice suppress both interleukin-2 (IL-2) production and IL-2 receptor expression. To try to identify the regulatory level by which the T-cell activation is switched off, we have analysed the potential of the suppressive macrophage-like cells to block the secretion of the accessory cell-derived T cell co-stimulator interleukin-1 (IL-1). The IL-1 secretion, however, was found to be greatly increased rather than decreased. The increased secretion was in part caused by an increased release rather than by an increased synthesis. In the presence of an in vitro trigger (lipopolysaccharide), the IL-1 secretion was increased 20-30-fold by the infection whereas the total IL-1 production increased only 1.5-2-fold. Macrophages from infected mice thus manifested a marginally increased IL-1 synthesis but released a markedly larger proportion of the synthesized monokine than normal macrophages. In the absence of an in vitro trigger, the infection caused a 10-15-fold increase in IL-1 synthesis as a consequence of an in vivo preactivation. This increase was only observed when the synthesis of prostaglandins was blocked by addition of indomethacin.

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PubMed1987

Experimental Trypanosoma brucei infections selectively suppress both interleukin 2 production and interleukin 2 receptor expression.

Experimental infections with Trypanosoma brucei AnTat 1.1.E not only account for a suppression of interleukin 2 (IL 2) production, but also induce an impairment of IL 2 receptor expression. Indeed, lymph node cells derived from infected mice failed to express IL 2 receptors following mitogenic stimulation as compared to normal controls. This impairment was not attributed to a modulation of the number of T cells and was not caused by the presence of living parasites. Furthermore, the basal level of IL 2 receptor expression could not be re-established through the exogenous supply of recombinant IL 2. This impairment of receptor expression was found to be mediated by suppressive cells that affect the relative number of receptor-positive cells as well as the mean receptor density. On the other hand, the mitogen-induced secretion of other T cell-derived lymphokines was not inhibited during infection, indicating that the severe suppression of IL 2 regulation was not attributed to a total paralysis of the T cell responsiveness.

Animals↗
PubMed1986

Active suppression of interleukin 2 secretion in mice infected with Trypanosoma brucei AnTat 1.1.E.

Impairment of T cell proliferation in mice infected with the pleomorphic Trypanosoma brucei AnTat 1.1 E clone was found not to be related to a depletion of T cells or to an absence of functional accessory cells, but rather to an active suppression of interleukin 2 (IL-2) production. Lymph node cells derived from infected mice failed to produce IL-2 following Con A stimulation, whereas an exogenous supply of recombinant IL-2 could restore the impairment of the mitogen (Con A)-induced proliferative responses. Furthermore, lymph node cells derived from infected mice suppressed both secondary T-cell proliferative responses and IL-2 secretion, indicating that the trypanosome-induced suppression is mediated by a suppressive cell which interferes at the level of IL-2 secretion.

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PubMedDate not supplied

[Lymphocyte system and relative resistance of inbred mice to Trypanosoma brucei brucei].

The distribution of B-(Ig+) and T-(Thy1.2+, Lyt1+, Lyt2+) lymphocyte subsets in murine lymphoid organs was analysed by immunofluorescence (FACS) on cell suspensions throughout a primary infection of C3H/He (susceptible) and CBA/Ca (subtolerant) inbred mice with metacyclic Trypanosoma brucei brucei EATRO 1125. A direct correlation was observed between (1) the level of first-peak parasitaemia, (2) its subsequent control by the host and (3) survival time. In the course of the infection, the overall population of spleen and lymph node lymphocytes was subject to polyclonal activation whilst the proportion of differentiated B and T subsets decreased accordingly. No correlation was found between modulation of the lymphocyte system and susceptibility to trypanosomiasis.

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