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Biomedical subjects

A Zlotnik

Publications and source records attributed to A Zlotnik.

135 records · Page 8Linked to original sources
PubMed1985

Enhancing effects of gamma interferon on phagocytic cell association with and killing of Trypanosoma cruzi.

The effects of gamma interferon (IFN-gamma) on P388D1 cell or mouse resident peritoneal macrophage association (i.e., binding and internalization) with the protozoan Trypanosoma cruzi were studied, as well as the effects of this lymphokine on intracellular parasite killing. Incubation of either type of cell with a conditioned medium containing IFN-gamma and traces of interleukin 2 markedly increased the capacities of the cells to associate with virulent blood forms of T. cruzi, as evidenced by significant increases in both the proportion of parasite-associated cells and the number of parasites associated with the cells. Three lines of evidence pointed to IFN-gamma, and not interleukin 2, as the lymphokine responsible for the noted effect. First, a conditioned medium containing interleukin 2 but not IFN-gamma failed to enhance P338D1 cell-parasite association. Second, treatment of the IFN-gamma preparation at pH 2 to selectively inactivate IFN-gamma reduced its enhancing effect. Third, recombinant IFN-gamma, devoid of other lymphokines, also enhanced parasite association with P388D1 cells. Incubation of P388D1 cells with IFN-gamma for 24, 48, or 72 h increased cell association with T. cruzi, whereas a 12-h incubation period was insufficient, suggesting that IFN-gamma triggered time-dependent cellular events leading to the enhancement. Treatment of mouse resident peritoneal macrophages with the IFN-gamma-containing conditioned medium also increased the capacity of these cells to kill internalized trypanosomes. P388D1 cells, which showed minimal or no cytotoxicity after mock treatment with medium, displayed cytotoxicity after incubation with the IFN-gamma-containing conditioned medium; similar results were obtained with recombinant IFN-gamma. Catalase prevented parasite killing by P388D1 cells, indicating that H2O2 mediated the cytotoxicity. These results, underscoring the regulatory effects of IFN-gamma on macrophage-parasite interactions, suggest a possible role for this lymphokine in the mechanisms of host defense active against T. cruzi infection.

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PubMed1984

Interleukin-induced increase in Ia expression by normal mouse B cells.

The constitutive culture supernatant (SN) of the macrophage tumor line P388D1 (P388 SN) and the concanavalin A (Con A)-induced culture supernatant of the T cell hybridoma FS6-14.13 (FS6 Con A SN) were shown to contain nonspecific factors capable of inducing increased Ia expression by normal resting B cells in a dose-dependent manner. In six consecutive experiments the relative increase in Ia expression induced by P388 SN was 4.9 +/- 0.9, with FS6 Con A SN 10.7 +/- 1.5, and with a combination of both preparations 13.0 +/- 1.7. This increase in Ia expression was observed to occur in virtually all the B cells, reaching maximum levels within 24 h of culture. The interleukin-induced increase in B cell Ia expression occurred in the absence of ancillary signals provided by ligand-receptor Ig cross-linking and despite the fact that virtually all the control B cells, cultured in the absence of factors, remained in G0. These results suggest that functional receptors for at least some interleukins are expressed on normal resting B cells and their effects can be manifest in the absence of additional activating signals. The increased Ia expression induced by the nonspecific factor preparations was shown to be correlated with enhanced antigen-presenting capacity by the B cells to T cell hybridomas. The nature of the interleukins responsible for these effects remains to be definitively determined, however, the activity of FS6 Con A SN was shown to correlate with B cell growth factor activity and increased B cell Ia expression was not observed using interleukin 2 (IL-2) or interferon-gamma, prepared by recombinant DNA technology.

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PubMed1984

T-cell hybridoma-produced lymphokine that activates macrophages to suppress intracellular growth of Histoplasma capsulatum.

Supernatants from concanavalin A-stimulated T-cell hybridomas activated macrophages to suppress the intracellular growth of Histoplasma capsulatum and to kill tumor cells. The supernatants had high interferon activity and were pH 2 sensitive and heat resistant. Gamma interferon is suggested to be among the active substances in the supernatants. Neither alpha interferon nor beta interferon activated macrophages for the Histoplasma growth inhibitory activity.

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PubMed1983

The major histocompatibility complex-restricted antigen receptor on T cells. II. Role of the L3T4 product.

We have examined the role of the murine homologue of Leu-3 T4, L3T4, in recognition of antigen in association with products of the major histocompatibility complex (Ag/MHC) by murine T cell hybridomas. A series of ovalbumin (OVA)/I-Ad-specific T cell hybridomas were ranked in their sensitivity to Ag/I by measuring their ability to respond to low doses of OVA, or their sensitivity to inhibition by anti-I-Ad antibodies. T cell hybridomas with low apparent avidity for OVA/I-Ad, i.e. that did not respond well to low concentrations of OVA and were easily inhibited by anti-I-Ad, were also easily inhibited by anti-L3T4 antibodies. The reverse was true for T cell hybridomas with apparent high avidity for Ag/MHC. We found that the presence of low doses of anti-L3T4 antibodies caused T cell hybridomas to respond less well to low doses of Ag, and to be more easily inhibited by anti-I-Ad antibodies. These results suggested that the role of the L3T4 molecule is to increase the overall avidity of the reaction between T cells and Ag-presenting cells. In support of this idea was the discovery of several L3T4- subclones of one of our L3T4+ T cell hybridomas, D0.11.10. The L3T4- subclones had the same amount of receptor for OVA/I-Ad as their L3T4+ parent, as detected by an anti-receptor monoclonal antibody. The L3T4- subclones, however, responded less well to low doses of OVA, and were more easily inhibited by anti-I-Ad antibodies than their L3T4/ parent. These results showed that the L3T4 molecule was not required for surface expression of, or functional activity of, the T cell receptor for Ag/MHC. The L3T4 molecule did, however, increase the sensitivity with which the T cell reacted with Ag/MHC on Ag-presenting cells.

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PubMed1983

Characterization of the gamma-interferon-mediated induction of antigen-presenting ability in P388D1 cells.

We characterized an assay system to study the lymphokine-mediated induction of antigen-presenting ability in P388D1 cells. The ability of lymphokine-induced P388D1 macrophages to present antigen plus Id was measured by their ability to induce interleukin 2 production by antigen-specific, Id-restricted T cell hybridomas in the presence of the appropriate antigen. The production of IL 2 by the T cell hybridomas is known to be dependent on the expression of Ia antigens by the antigen-presenting cells. The results obtained suggest that a factor present in the supernatant of the T cell hybridoma FS7-20.6.18 is responsible for inducing the appearance of I-Ad and I-Ed on P388D1, measured by immunofluorescence, and the ability of the cell to present antigen in association with I-Ad or I-Ed. The factor mediating the induction of antigen-presenting ability is thought to be gamma-interferon, because the hybridoma FS7-20.6.18 is known to produce this lymphokine and the factor is sensitive to pH 2 incubation. gamma-Interferon produced by recombinant DNA technology was found to induce antigen-presenting ability in this assay; however, alpha- and beta-interferon were inactive. This observation suggests a unique immunoregulatory role for gamma-interferon. Using many T cell hybridomas in the assay, we were able to distinguish three groups: a) high avidity hybridomas that respond to antigen presented by uninduced P388D1 but show an enhanced response to antigen plus induced P388D1; b) medium avidity hybridomas that do not respond to antigen presented by uninduced P388D1; and c) low avidity hybridomas that show a limited response to antigen presented by induced P388D1, but the response of which increases if the P388D1 cells are induced for longer periods of time. These different patterns of response are believed to be dependent on the Ia antigen density expressed by the gamma-interferon-induced presenting cells, and suggest that the T cell receptors for Ag/Id display marked heterogeneity in their avidities for Ag/Id.

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PubMed1983

Coordinate production by a T cell hybridoma of gamma interferon and three other lymphokine activities: multiple activities of a single lymphokine?

The T cell hybridoma FS7-20, produced by the fusion of normal B10.BR T cells to the AKR thymoma BW5147, was found when stimulated with concanavalin A (Con A) to produce the lymphokines: interleukin 2 (IL 2), interferon-gamma (IFN gamma), macrophage-activating factor (MAF), Ia induction factor IaIF), and the B cell helper factor interleukin X (IL X). The clones and subclones of FS7-20 varied dramatically in their ability to produce these lymphokines, presumably because of karyotypic variations. The ability to produce IL 2 segregated independently from the ability to produce the four other lymphokine activities; however, production of the latter activities showed a strong correlation. This coordinate production of IFN gamma, MAF, IaIF, and IL X was also observed with a cloned normal cytotoxic T cell line, cr15. These results suggest either that IFN gamma, MAF, IaIF, and IL X are all manifestations of a single molecular species or that, although these activities are different structurally, their production is controlled by a common genetic mechanism. In support of the first possibility, the IFN gamma, MAF, IaIF, and IL X activity produced by FS7-20 were all found to be equally sensitive to inactivation at pH 2. These results illustrate the usefulness of using T cell hybridomas for the study of lymphokines.

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PubMed1982

Lymphokine-induced mycobacteriostatic activity in mouse pleural macrophages.

We have developed an in vitro assay to study the intramacrophage replication of Mycobacterium tuberculosis or Mycobacterium bovis BCG. In this assay, extracellular mycobacterial replication was avoided by using a small infecting inoculum and a new method for efficiently removing nonphagocytocytized bacilli. The ability of different mycobacterial strains to replicate in mouse pleural macrophages correlated with their virulence. The effect of lymphokines prepared by incubating spleen cells from BCG-immunized mice with mycobacterial antigens was tested with this assay. In the presence of lymphokines, mouse pleural macrophages were able to inhibit the intramacrophage replication of both BCG and M. tuberculosis. This assay is a useful in vitro model for studying antibacterial cellular immunity expressed by macrophages.

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PubMedDate not supplied

Role of gamma-interferon in antibody-producing responses.

Interferon preparations, especially those containing gamma-interferon (IFN-gamma), have long been known to modulate immune responses. However, because many studies used only partially purified interferons, it has been difficult to separate the immunoregulatory effects of the interferons from those of other biologically active molecules contaminating the preparations. Recently, with the cloning of the interferon genes in mouse and man, it has become possible to use these cloned interferons directly to test their effects in assays other than those involving the protection of cells from viruses. For example, cloned IFN-gamma has been shown to be a potent inducer of Ia antigen expression on macrophages. Similarly, cloned IFN-gamma has been reported to act as a macrophage activation factors, as judged by the ability of activated macrophages to kill tumour cells in vitro. We demonstrate here that cloned murine IFN-gamma can also substitute for a late-acting helper factor which acts synergistically with other helper factors in the stimulation of B-cell antibody responses in vitro.

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