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B Bonavida

Publications and source records attributed to B Bonavida.

At least 91 records · Page 5Linked to original sources
PubMed1993

Sensitivity of drug-resistant human ovarian tumor cell lines to combined effects of tumor necrosis factor (TNF-alpha) and doxorubicin: failure of the combination to modulate the MDR phenotype.

We have examined four human ovarian tumor lines (A2780, AD10, OVC-8, and SKOV-3) selected for their sensitivity and/or resistance to the recombinant human tumor necrosis factor alpha (TNF-alpha) and the chemotherapeutic drug doxorubicin (DOXO). The tumor lines were either sensitive to both agents, resistant to one or the other, or resistant to both. Of the four lines examined only the DOXO-resistant line AD10 exhibited the multidrug-resistance (MDR) phenotype. Enhanced cytotoxicity was seen with the combination of TNF-alpha and DOXO in each line regardless of their sensitivity or resistance patterns and, thus, demonstrates that drug resistance due to the expression of the MDR phenotype or its absence can be overcome by TNF-alpha and DOXO. We then examined whether TNF-alpha or TNF-alpha and DOXO modulated the MDR phenotype in AD10 as a possible mechanism of overcoming drug resistance. TNF-alpha had no effect on either DOXO intake or efflux as measured by flow cytometry. Further, TNF-alpha treatment showed no effect on the level of MDR-1 mRNA. These results suggest that the enhanced cytotoxicity seen with the combination of TNF-alpha and DOXO is not the result of any modulation of drug influx or efflux levels by TNF-alpha. Overall, these findings suggest that combination treatment with TNF-alpha and DOXO can overcome resistance inflicted by different mechanisms.

Doxorubicin↗
PubMed1993

Cytotoxic properties of a new synthetic demethylpodophyllotoxin derivative, BN 58705, against human tumor cell lines.

The in vitro cytotoxic properties of a newly synthesized demethylpodophyllotoxin derivative, 4-o-butanoyl-4'-demethylpodophyllotoxin (BN 58705), were determined by using several human tumor cell lines of different histological origin and of different sensitivity to conventional chemotherapeutic drugs (Adriamycin and cis-diammine-dichloride platinum). BN 58705 is shown to be cytotoxic against various human tumor cell lines as assessed by the MTT assay. Furthermore, BN 58705 is shown to be cytotoxic against several drug-resistant tumor cell lines. BN 58705 is cytotoxic at concentrations 100- to 1000-fold lower than those of Adriamycin or cis-diammine-dichloride platinum required to achieve similar cytotoxicity. BN 58705 did not mediate DNA fragmentation of target cells, whereas the epipodophyllotoxin-like etoposide induced DNA cleavage by stabilizing the DNA-enzyme intermediate. Like vinca alkaloids, BN 58705 induced a block in the mitotic phase of the cell cycle. By comparison, BN 58705 exerted a stronger cytotoxic activity in vitro than did either etoposide, an epipodophyllotoxin, or vincristine, a vinca alkaloid. When BN 58705 was applied in vivo in mice, it resulted in low toxicity (50% lethal dose, 150 mg/kg). These results demonstrate than BN 58705 is cytotoxic to drug-resistant human tumor cell lines and is manyfold more potent than conventional drugs. The cytotoxic potency and low toxicity of BN 58705 are important criteria to establish its potential chemotherapeutic efficacy in vivo.

Animals↗
PubMed1993

Sensitivity of human renal cell carcinoma lines to TNF, adriamycin, and combination: role of TNF mRNA induction in overcoming resistance.

We have examined 6 human renal cell carcinoma (RCC) cell lines for their sensitivity and resistance to the cytolytic effect of tumor necrosis factor (TNF) and adriamycin (ADR), alone or in combination. The results of cytotoxicity mediated by TNF and ADR showed no direct correlation as TNF resistant lines were sensitive to ADR while the TNF sensitive lines were resistant. The combination of TNF and ADR resulted in enhanced cytotoxicity against the tumor lines. Induction of TNF mRNA and protein has been suggested as a mechanism of resistance to TNF in certain tumors. Resistant and sensitive lines were capable of upregulating TNF mRNA after treatment with TNF or PMA+ionophore for periods as short as 1 hour, but only the resistant lines were able to secrete detectable levels of TNF protein. Therefore, a positive correlation existed between resistance to TNF and production and secretion of TNF by the cell lines. In the presence of the protein synthesis inhibitor cycloheximide (CHX), the TNF mRNA level in the TNF resistant lines was increased while the sensitive lines required an additional signal, such as exogenous TNF, to upregulate the mRNA. Due to the enhanced cytotoxicity seen with the combination of TNF and ADR, we determined the effect of this combination on the levels of TNF mRNA. As examined in a constitutively TNF expressing line, ADR alone reduced the constitutive mRNA level and, in combination with TNF, reduced the level of induction produced by TNF. This downregulation of TNF mRNA by ADR may play a role in the enhanced cytotoxicity seen with combined TNF and ADR treatment. The present study demonstrates that RCC cell lines differ in their sensitivity and/or resistance to TNF. Further, ADR and/or TNF resistant RCC lines can be rendered sensitive by combining TNF and ADR. The constitutive and/or inductive secretion of TNF by certain lines and its relationship to tumor pathogenesis as well as overcoming resistance are discussed.

Carcinoma, Renal Cell↗
PubMed1993

Regulation of B-cell lymphoma growth in syngeneic SJL/J mice. establishment of tumor dormancy following administration of anti-CD4 monoclonal antibody into tumor-bearing mice.

The spontaneously arising B-cell lymphoma (la+ reticulum cell sarcoma, RCS) in SJL/J mice has been shown to depend on host CD4 T cells for proliferation and growth. Treatment of mice with CD4 monoclonal antibody (mAb) prior to or after inoculation of a lethal dose of RCS tumor cells inhibits cell growth and the mice survive. The mechanism of tumor growth inhibition was studied by adoptively transferring cells from CD4 mAb treated tumor bearers into naive syngeneic mice. The recipient mice developed tumors and died. Tumor growth was dependent on the concentration of the adoptively transferred tumor cells. These results suggested that a state of tumor dormancy was established in the treated mice. Tumor dormancy was long lasting, as cells transferred as late as 11 weeks after the initial RCS inoculation still developed tumors in the recipient. The maintenance of dormancy was not due to failure of the recipient mice to mount an anti-tumor response or to the induction of suppressor cells. These results suggest that in the absence of CD4 cells, the RCS tumor remains dormant and this state of dormancy persists for long periods after total recovery of the CD4 cell subpopulation. Thus, it appears that RCS proliferation and growth is dependent on host CD4 cells but maintenance is under the influence of other cells or factors. Further characterization of this tumor dormant system and its regulation by the host may reveal novel mechanisms of tumor dormancy.

Animals↗
PubMed1993

[TNF and TNF receptors: structure, mechanism of action, role in disease and therapy].

In this article, the topics on TNF and TNF receptors presented in the 4th International Conference on Tumor Necrosis Factor and Related Cytokines (Netherlands, May, 1992) are briefly summarized in Japanese, based on Dr. Benjamin Bonavida's report (Cancer Update, supplement 8, 1992) with permission. Following categorized themes were discussed in the meeting: 1) regulation of TNF synthesis, especially at the transcriptional level, 2) TNF receptors, including type I (55 kd), type II (75 kd) and soluble forms, 3) TNF cytotoxicity and immunomodulation with considerations for mechanisms, 4) TNF and infectious diseases such as Plasmodium falciparum infection, 5) TNF and inflammatory diseases such as rheumatoid arthritis and 6) TNF and cancer, in attempts to overcome drug resistance and TNF toxicity.

Arthritis, Rheumatoid↗
PubMed1992

Sensitivity of resistant human tumor cell lines to tumor necrosis factor and adriamycin used in combination: correlation between down-regulation of tumor necrosis factor-messenger RNA induction and overcoming resistance.

A number of human tumor cell lines of various histological origin were examined for their sensitivity and resistance to tumor necrosis factor-alpha (TNF) and Adriamycin (ADR). Six ovarian lines, and one each of a renal, lung, and B-cell line, were tested for putative mechanisms of resistance to these agents. Cytotoxicity resulting from TNF or ADR showed no overall correlation in these lines. The combination of TNF and ADR produced enhanced cytotoxicity against these tumor lines and furthermore resulted in overcoming the resistance of TNF or ADR alone or in combination. A proposed mechanism of TNF resistance in tumor cells is the endogenous production of TNF mRNA and protein. There was a positive correlation between resistance to TNF and the constitutive production of TNF mRNA and protein. The TNF-resistant lines that did not constitutively produce TNF mRNA and protein and the three TNF-sensitive tumor lines exhibited up-regulation of their TNF mRNA in the presence of TNF or phorbol myristate acetate/ionophore, but did not secrete any detectable protein. Due to the enhanced cytotoxicity seen with the combination of TNF and ADR, the effect of this combination on the level of TNF mRNA was examined. ADR alone reduced the constitutive level of TNF mRNA and in combination with TNF reduced the level of induction produced by TNF. This down-regulation of TNF mRNA by ADR may play a role in the enhanced cytotoxicity seen with the combination of these 2 agents.

Down-Regulation↗
PubMed1992

Diphtheria toxin- and Pseudomonas A toxin-mediated apoptosis. ADP ribosylation of elongation factor-2 is required for DNA fragmentation and cell lysis and synergy with tumor necrosis factor-alpha.

We have reported that diphtheria toxin (DTX) mediates target cell lysis and intranucleosomal DNA fragmentation (apoptosis) and also synergizes with TNF-alpha. In this paper, we examined which step in the pathway of DTX-mediated inhibition of protein synthesis was important for induction of cytolytic activity and for synergy. Using a DTX-sensitive tumor cell line, we first examined the activity of the mutant CRM 197, which does not catalyze the ADP ribosylation of elongation factor-2 (EF-2). CRM 197 was not cytolytic for target cells and did not mediate intranucleosomal DNA fragmentation of viable cells. The failure of CRM 197 to mediate target cell lysis suggested that the catalytic activity of DTX is prerequisite for target cell lysis. This was corroborated by demonstrating that MeSAdo, which blocks the biosynthesis of diphthamide, inhibited DTX-mediated protein synthesis inhibition and also blocked target cell lysis. Furthermore, the addition of nicotinamide, which competes with NAD+ on the DTX action site of EF-2, also blocked DTX-mediated lysis. These findings suggest that ADP-ribosylation of EF-2 may be a necessary step in the pathway leading to target cell lysis. In contrast to the sensitive line, the SKOV-3 tumor cell line is sensitive to protein synthesis inhibition by DTX but is not susceptible to cytolysis and apoptosis by DTX. Thus, protein synthesis inhibition by DTX is not sufficient to mediate target cell lysis. The synergy in cytotoxicity obtained with the combination of DTX and TNF-alpha was examined in order to determine the pathway mediated by DTX in synergy. Like the direct lysis by DTX, synergy was significantly reduced by MeSAdo and by nicotinamide. Furthermore, synergy was not observed with combination of CRM 197 and TNF-alpha. These results demonstrate that, in synergy, DTX may utilize the same pathway required for its cytolytic activity. Pseudomonas aeruginosa exotoxin shared most the properties shown for DTX. Altogether, these findings demonstrate that DTX-mediated apoptosis is initiated at a step beyond the ADP ribosylation of EF-2.

ADP Ribose Transferases↗
PubMed1992

Hierarchy of in vitro sensitivity and resistance of tumor cells to cytotoxic effector cells, cytokines, drugs and toxins.

Drug resistance of tumor cells has led to the development of other therapeutic modalities including biological response modifiers, lymphokine-activated killer cells (LAK), and cytokines alone and in combination. The premise of these alternative modalities is that drug resistance can be overcome by other cytotoxic agents or cytotoxic effector cells. However, the relationship between tumor cell sensitivity to these different agents and the cytotoxicity caused by drugs is not known or well understood. Thus, understanding the relationship between these different systems of tumor cell cytotoxicity is essential for optimal therapeutic intervention. To this end, we compared the tumor cell cytotoxicity mediated by recombinant tumor necrosis factor (rTNF), cytotoxic effector cells (natural killer cells, monocytes, LAK cells), chemotherapeutic drugs, and microbial toxins. Human tumor cell lines sensitive and resistant to rTNF or drugs were used to evaluate the effectiveness of the other cytotoxic modalities. Sensitivity was considered as tumor cell cytotoxicity above 15% while resistance refers to that below 10%. Cell lines tested consisted of several histological types such as brain, lung, colon and ovarian tumors. In our experiments, cell lines made resistant to rTNF by coculture were also relatively resistant to unactivated monocytes and their supernatants. These lines were sensitive to all other methods tested including activated monocytes, natural killer and LAK cells, drugs, and toxins. The tumor lines naturally resistant to rTNF were found to have various degrees of sensitivity and resistance to these other systems. Upon the analysis of our data, a pattern emerged that suggested a hierarchy of sensitivity and resistance of the tumor cells to the cytotoxic mechanisms explored. From a majority of cell lines resistant to rTNF to a minority of lines resistant to LAK, we found an interesting gradation of sensitivity and/or resistance to the other cytotoxic modalities employed. The hypothesis of an underlying common mechanism of action within these systems is discussed.

Bacterial Toxins↗
PubMed1991

Synergistic effect of tumor necrosis factor-alpha- and diphtheria toxin-mediated cytotoxicity in sensitive and resistant human ovarian tumor cell lines.

Recent studies have demonstrated that diphtheria toxin (DTX) also mediates target cell lysis, and the mechanism of cytotoxicity has many features similar to those of cytotoxicity mediated by TNF-alpha. Thus, we hypothesized that DTX and TNF-alpha, used in combination, may result in either additive or synergistic cytotoxic activity. This was examined on three human ovarian carcinoma cell lines chosen for their differing sensitivities to TNF-alpha and DTX, i.e., 222, which is sensitive to both TNF-alpha and DTX, 222TR, a TNF-alpha-resistant DTX-sensitive variant of 222, and SKOV-3, which is resistant to both DTX and TNF-alpha. The simultaneous use of DTX and TNF-alpha at suboptimal concentrations resulted in synergistic cytotoxic activity against all three lines tested, thus overcoming the TNF-alpha resistance of 222TR and the double resistance of SKOV-3. DNA fragmentation was observed in all three lines treated with DTX and TNF-alpha and occurred as early as 4 h after treatment. Cycloheximide, actinomycin D, or emetine, at concentrations causing greater than 90% protein synthesis inhibition, did not result in cytotoxicity alone or synergy with TNF-alpha, suggesting that synergy by DTX was not due to its ability to inhibit protein synthesis. The use of energy poisons and pH conditions that inhibit DTX-mediated cytotoxicity resulted in the abrogation of synergy. These findings show that the two cytotoxic agents TNF-alpha and DTX, when used at suboptimal concentrations, synergize in their cytotoxic activity against sensitive and resistant cell lines. Because the SKOV-3 cell line used here is also resistant to chemotherapeutic drugs, combination treatment with DTX and TNF-alpha may be beneficial in overcoming drug resistance.

Ammonium Chloride↗
PubMed1990

Antibody-dependent cellular cytotoxicity against HIV-coated target cells by peripheral blood monocytes from HIV seropositive asymptomatic patients.

Cytotoxic effector cells like cytotoxic T cells, NK cells, monocytes/macrophages, and neutrophils can lyse directly HIV-infected or HIV-coated cells in the absence or presence of anti-HIV antibodies. Therefore, these cytotoxic mechanisms can be invoked either in the control of HIV infection at early stages of the disease or in the generalized immunosuppression observed at later stages of the disease. The relationship between anti-HIV effector mechanisms and disease, however, remains elusive. The present study investigates in HIV+ seropositive asymptomatic patients peripheral blood monocytes (PBM)-mediated antibody dependent cellular cytotoxicity (ADCC) against HIV-coated target cells in the presence of heterologous or autologous anti-HIV serum. To test for specific ADCC against HIV Ag, a T4+ CEM.TR line resistant to TNF and macrophage-mediated cytotoxicity was selected in vitro. ADCC was performed in an 18-h 51Cr-release assay using CEM.TR cells coated with inactivated HIV. Unlike PBM from normal controls, significant ADCC was observed by PBM from HIV+ seropositive patients in the presence of pooled HIV+ antiserum. The ADCC activity was specific for HIV and was dependent on the E:T ratio and the antiserum dilution used. Upon activation of PBM with rIFN-gamma, both normal and HIV+ PBM-mediated ADCC against HIV-coated CEM.TR. Furthermore, ADCC activity by PBM from HIV+ seropositive patients in the presence of their autologous serum was examined. Significant ADCC activity was observed and was dependent on the E:T ratio and serum dilution used. The findings demonstrating anti-HIV ADCC activity by PBM from HIV+ seropositive individuals and their autologous sera support the notion that monocyte-mediated ADCC may be operative in vivo.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1990

Cycloheximide-induced modulation of TNF-mediated cytotoxicity in sensitive and resistant ovarian tumor cells.

The mechanism of sensitivity and resistance of various ovarian carcinoma lines to recombinant tumor necrosis factor (rTNF)-mediated cytotoxicity has been investigated using a 24-h 51Cr-release assay. The cell line PA-1 is sensitive to TNF in a dose-dependent manner, whereas the cell line SKOV-3 is resistant to TNF even at high concentrations. The simultaneous addition of TNF and cycloheximide (CHX) in the assay converted the resistant SKOV-3 line into a sensitive line, but no detectable change was observed with PA-1. rTNF inhibited DNA, RNA, and protein synthesis of the sensitive PA-1 line, whereas it had no effect on SKOV-3. This finding was not due to differences in the expression of TNF receptors, as both cell lines expressed equivalent numbers of receptors. The addition of CHX to TNF resulted in suppression of DNA, RNA, and protein synthesis in both the sensitive and the resistant cell lines. Pretreatment of the cell line with TNF for 3 h and subsequent washing resulted in significant cytotoxicity of the sensitive PA-1 line and some cytotoxicity against SKOV-3. However, if the cells were pretreated with CHX for 3 h followed by rTNF for 24 h, a significant decrease in cytotoxicity was observed in both cell lines. Under these conditions, there was no significant inhibition of DNA, RNA, or protein synthesis. Pretreatment of cells for 24 h with TNF and 24 h with CHX resulted in augmentation of the cytotoxicity of PA-1 and SKOV-3, whereas pretreatment for 24 h with CHX followed by 24 h with TNF resulted in no cytotoxicity. Cells pretreated with CHX for 24 h showed poor binding of [125]I-TNF and poor internalization, whereas cells pretreated for 24 h with TNF showed marked enhancement of internalization. The sensitivity of freshly derived ovarian carcinoma lines to TNF and CHX demonstrated that TNF-resistant cells became more sensitive if treated with CHX. These results demonstrate the potential use of metabolic inhibitors in increasing the sensitivity of fresh ovarian tumor cells to TNF.

Cell Survival↗
PubMed1990

Peripheral blood monocytes derived from HIV+ individuals mediate antibody-dependent cellular cytotoxicity (ADCC).

Monocytes/macrophages serve a number of immunologic functions and play a major role in the host defense against infection. Abnormal functions of monocytes have been reported in AIDS and HIV+ individuals. A recent report from our laboratory demonstrated that peripheral blood monocytes (PBM) derived from AIDS patients were de novo "activated" as assessed by direct cell-mediated cytotoxicity (CMC) and secretion of cytotoxic factors and tumor necrosis factor-alpha (TNF alpha). Thus, both the direct cytotoxicity as well as the antibody-dependent cellular cytotoxicity (ADCC) exerted by the monocytes may contribute to the destruction of HIV-infected/coated cells and the immunopathogenesis of AIDS. The present study investigated the ability of HIV+ PBM to mediate ADCC against antibody-coated target cells in an 18-hr 51Cr release assay. Initial studies examined ADCC using a macrophage resistant target Raji and rabbit anti-Raji serum. The results show that the majority of PBM from HIV+ individuals mediate ADCC activity while the majority of PBM from normal healthy controls was not cytotoxic. While activation of PBM with recombinant interferon-gamma (rIFN-gamma) enhances the ADCC activity of normal PBM, treatment of HIV+ PBM with IFN-gamma resulted in significant enhancement of ADCC. Both untreated and treated PBM from HIV+ individuals had significantly higher ADCC than PBM from normal individuals. Of interest, a significant ADCC activity was found by PBM derived from two HIV- high risk individuals whether untreated or treated with rIFN-gamma. The ADCC results with RAJI target cells prompted us to investigate whether ADCC can also be obtained using HIV-infected T4+ cells. We selected a macrophage and TNF resistant T4+ CEM cell line as target for ADCC. The target was coated with inactivated HIV and pooled human anti-HIV serum was used. Studies with a few HIV+ individuals demonstrate that significant ADCC is obtained with PBM from HIV+ individuals but little or no ADCC by normal PBM and the ADCC was specific for HIV. The ADCC was also significantly enhanced by treatment of PBM with rIFN-gamma. The results of this study clearly indicate that PBM from HIV+ individuals are endowed with the capacity to mediate ADCC against HIV-infected/coated cells and thus, we postulate that PBM may play a direct role in vivo in lysis or suppression of HIV-coated/infected cells and in the pathogenesis of AIDS.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1990

Synergy is documented in vitro with low-dose recombinant tumor necrosis factor, cisplatin, and doxorubicin in ovarian cancer cells.

Ovarian carcinomas have been shown to be sensitive or insensitive to the in vitro exposure of several cytotoxic drugs and cytokines. Because of the potential for cytokines to enhance the efficacy of chemotherapeutic agents and to improve their therapeutic index, the optimal dose and schedule of the combination of these agents have been studied. We examined the cytotoxic effect of a combined modality using a variety of concentrations of recombinant tumor necrosis factor (rTNF) (a cytotoxic cytokine) with Adriamycin (ADR) and cisplatin (CDDP) on human ovarian carcinoma cell lines. Cytotoxicity was determined in a 24-hr 51Cr-release assay and confirmed in a 5-day viability culture assay. Five cell lines were used: PA-1, 222, OVCAR-3, SKOV-3, and OVCAR-8. Doses of rTNF that were minimally cytotoxic resulted in significant cytotoxicity and synergy when used with optimal or suboptimal concentrations of ADR or CDDP. This synergy was observed in four cell lines. Interestingly, the rTNF- and drug resistant SKOV-3 cell line was sensitive to the synergistic effect of Adriamycin and rTNF. The synergistic effect that was obtained was specific to rTNF, while the combined use of ADR and CDDP or recombinant interleukin-2 and cytotoxic drugs had no synergistic effect on tumor cell lysis. Further, the addition of anti-TNF antibody abrogated the synergistic effect seen with rTNF and the cytotoxic drugs. These studies demonstrate clearly that significant synergistic antitumor cytotoxic activity against human ovarian carcinoma cell lines can be achieved with combinations of low doses of rTNF and ADR or CDDP, suggesting their possible adaptation in vivo for cancer therapy. Further, the studies suggest that rTNF and the cytotoxic drugs tested may share a common lytic pathway. Since rTNF used alone has been relatively inactive in clinical trials, its potential activity may be apparent only when combined with conventional cytotoxic chemotherapeutic agents and when administered in relatively low concentration.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1990

Purification and characterization of cytolytic and noncytolytic human natural killer cell subsets.

Natural killer (NK) cells form three functionally distinct populations of effectors: competent cytolytic effectors able to bind and kill target cells and two subsets of nonlytic effectors, one able and the other unable to bind target cells. A flow cytometric method was developed, based on size and two-color fluorescence of NK cell-target conjugates, for the characterization and sorting of highly purified subpopulations--killer cells, nonkiller binder cells, and free cells. Ultrastructural examination revealed that granule content was reduced in the killer cells and absent in most of the binder cells. Quantitative differences in the expression level of HLA class I, CD11b (C3bi receptor), and CD16 (receptor for the Fc portion of IgG) antigens could differentiate the subsets. The killer phenotype was HLAlo, CD11bvery hi, and CD16very lo; the binder phenotype was CD11bhi and CD16lo; and the free-cell phenotype was CD11blo and CD16hi. Cell activation was not requisite for lytic function because no difference in either expression of activation markers or cell cycle could be established among the sorted subpopulations. Although recycling function was inhibited, retention of lytic activity was enriched 4-fold in the sorted killer cell population. These results represent characterization of a successful bulk isolation of competent killer, nonkiller binder, and free cells in human NK-cell populations and should aid our understanding of NK-cell development, lineage, and function.

Antibodies, Monoclonal↗
PubMed1990

Effects of platelet-activating factor on peripheral blood monocytes: induction and priming for TNF secretion.

Inflammatory-type responses are complex events involving several cellular interactions and several cytokines. Both the monocytes/macrophages and platelet-activating factor (PAF) play an important and central role in inflammatory responses. Accordingly, we investigated the effects of PAF on function and priming of human peripheral blood monocytes (PBM). Several observations were made that demonstrated that PBM respond to PAF stimulation. The addition of PAF to freshly isolated PBM triggered the release of tumor necrosis factor (TNF) in the supernatant in the absence of induction of macrophage-mediated cytotoxicity, unlike interferon-gamma (IFN-gamma) or lipopolysaccharide (LPS). Secretion of TNF was detected shortly after addition of PAF and was dependent on the PAF concentration used. By 4-6 h, the level of TNF, as detected by radioimmunoassay, reached a plateau and remained the same for 24 h. While biologically active and cytotoxic TNF was detected early after addition of PAF, the cytotoxic activity declined thereafter though the antigenic activity remained constant. Supernatants derived from PAF-treated PBM contained an inhibitor of TNF biological activity. We then examined whether PBM can be primed with PAF and respond to a secondary challenge. PBM primed with PAF respond by secreting TNF to both phorbol myristate acetate and concanavalin A but respond poorly to PAF, LPS, or IFN-gamma. These results suggest that following priming, PBM remain refractory to specific secondary stimuli but can still respond to non-specific stimuli. Overall, the present findings demonstrate that PAF can directly interact with PBM and regulate their functional activity. We suggest that PAF may mediate part of its biological activity via the macrophage and further, monocyte secretion of PAF can in turn regulate monocyte function. Further, cytokine secretion by PAF-activated PBM may contribute to the inflammatory process.

Calcium↗