Biomedical subjects

D L Longo

Publications and source records attributed to D L Longo.

At least 163 records · Page 9Linked to original sources

PubMed1994

Phosphorylation of NF-KB1-p50 is involved in NF-kappa B activation and stable DNA binding.

We have previously shown that NF-kappa B/Rel family members are physically associated phosphoproteins, and p105 and p50 are hyperphosphorylated after NF-kappa B activation. In this report, we further studied the phosphorylation involved in NF-kappa B activation in Jurkat T cells responding to phorbol 12-myristate 13-acetate and phytohemagglutinin. Immediately following stimulation, p50 is hyperphosphorylated, and a phosphorylated form of p50 (pp50) is translocated from the cytoplasm to the nucleus. The kinetics of this nuclear translocation paralleled that of the appearance of an active kappa B DNA-binding complex. An at least 30-fold higher level of kappa B DNA binding was detected in pp50 than p50. The enhanced binding could be attributed to a much greater stability detected in the complex consisting of kappa B DNA and pp50, but not p50. These results suggest that phosphorylation of p50, and perhaps other family members as well, may be involved in the activation of NF-kappa B/Rel family transcription factors.

Base Sequence↗

PubMed1994

NF-kappa B/Rel family members are physically associated phosphoproteins.

We performed radioimmunoprecipitation followed by serial immunoblots to show that, in the unstimulated Jurkat T cell line, the NF-kappa B/Rel family proteins, p80-c-Rel, p105-NF-kappa B, p65-NF-kappa B, p50-NF-kappa B and p36-I kappa B alpha, can be detected as complexes using antisera against c-Rel, p105-NF-kappa B or p65-NF-kappa B. p36-I kappa B alpha and p105, both known inhibitors of NF-kappa B function, can physically associate with NF-kappa B/Rel family members, but not with each other. In vivo and in vitro phosphorylation experiments demonstrated that NF-kappa B/Rel family members, including p105, c-Rel, p50, p65 (for the first time for p50 and p65) and p36-I kappa B alpha are also phosphoproteins. Phosphoserine and phosphothreonine residues were identified in these proteins isolated from unstimulated Jurkat cells. Both unphosphorylated and hyperphosphorylated forms of p36-I kappa B alpha were found in the complexes, suggesting that hyperphosphorylated I kappa B alpha is still capable of associating with the NF-kappa B/Rel family members. After stimulation with phorbol 12-myristate 13-acetate and phytohaemagglutinin for 10 min, p105-NF-kappa B and p50-NF-kappa B, but not p36-I kappa B, were highly phosphorylated. Phosphopeptide mapping of p105 showed that phorbol ester/phytohaemagglutinin stimulation may change p105 phosphorylation qualitatively.

Animals↗

PubMed1994

Recombinant transforming growth factor beta 1 and beta 2 protect mice from acutely lethal doses of 5-fluorouracil and doxorubicin.

Transforming growth factor beta 1 (TGF-beta 1) and TGF-beta 2 can reversibly inhibit the proliferation of hematopoietic progenitor cells in vivo, leading us to hypothesize that such quiescent progenitors might be more resistant to high doses of cell cycle active chemotherapeutic drugs, thereby allowing dose intensification of such agents. Initial studies showed that whereas administration of TGF-beta 1 or TGF-beta 2 did not prevent death in normal mice treated with high doses of 5-fluorouracil (5-FU), those mice that received TGF-beta 2 did exhibit the beginning of a hematologic recovery by day 11 after administration of 5-FU, and were preferentially rescued by a suboptimal number of transplanted bone marrow cells. Subsequently, it was found that the administration of TGF-beta 2 protected recovering progenitor cells from high concentrations of 5-FU in vitro. This protection coincided with the finding that significantly more progenitors for colony-forming unit-culture (CFU-c) and CFU-granulocyte, erythroid, megakaryocyte, macrophage (GEMM) were removed from S-phase by TGF-beta in mice undergoing hematopoietic recovery than in normal mice. Further studies showed that the administration of TGF-beta protected up to 90% of these mice undergoing hematologic recovery from a rechallenge in vivo with high dose 5-FU, while survival in mice not given TGF-beta was < 40%. Pretreatment of mice with TGF-beta 1 or TGF-beta 2 also protected 70-80% of mice from lethal doses of the noncycle active chemotherapeutic drug, doxorubicin hydrochloride (DXR). These results demonstrate that TGF-beta can protect mice from both the lethal hematopoietic toxicity of 5-FU, as well as the nonhematopoietic toxicity of DXR. This report thus shows that a negative regulator of hematopoiesis can be successfully used systemically to mediate chemoprotection in vivo.

Animals↗

PubMed1994

Induction of T cell differentiation and lymphomagenesis in the thymus of mice with severe combined immune deficiency (SCID).

Severe combined immune deficiency (SCID) mice have a defect in their recombinase system and cannot productively rearrange their immune receptor genes. Thus, SCID thymocytes are arrested at the immature "triple negative" phase, not expressing CD3, CD4, or CD8 surface markers. Whole body irradiation of SCID mice induced maturation of their thymocytes to the CD4+/CD8+ double positive, CD3+low stage of differentiation, and resulted in the generation of a thymic cortical region on histologic examination. No mature single positive T cells were detected in the thymus or the periphery. VDJ rearrangements of TCR-beta with restricted clonality were observed in the double positive cells from a given individual. The CD3 complex was expressed on some of these cells, but the cells failed to mobilize intracellular calcium after cross-linking with CD3 Abs. The double positive cells appeared several weeks after irradiation, persisted for many months in the thymus, and by 6 mo generally developed into metastatic lymphoma. Retroviral activation was undetectable in both the preneoplastic and transformed thymocytes. Thus, it appears that the earliest steps in T cell development can be induced in SCID mice by inducing DNA breaks with radiation. This system represents a model of early thymic development, preneoplasia, and neoplasia.

Animals↗

PubMed1994

Interleukin-1 (IL-1) directly and indirectly promotes hematopoietic cell growth through type I IL-1 receptor.

Interleukin-1 (IL-1) has been shown to stimulate hematopoietic progenitor cell growth both in vitro and in vivo. Although IL-1 alone lacks the ability to promote hematopoietic progenitor growth in vitro, it is a potent synergistic factor in combination with other colony-stimulating factors (CSFs). Because it was unknown whether type I (p80), type II (p68), or other IL-1-binding proteins mediated the synergistic effects of IL-1 on purified progenitor cells, we used the difference in immunoreactivity between type I and type II IL-1 receptor (IL-1R) to better assess the role of these receptors in hematopoietic progenitor growth. Therefore, the synergistic effects of IL-1 alpha on IL-3-, CSF-1-, and granulocyte macrophage (GM)-CSF-induced progenitor growth, both in CFU-c and single-cell assays, were determined in the presence of monoclonal antibodies (MoAbs) 35F5 and 4E2 that block the binding of IL-1 alpha to type I and type II IL-1R, respectively. The synergistic effect of IL-1 alpha on IL-3 responsive Lin- and Lin(-)-Thy-1+ progenitors was indirectly mediated and could be inhibited by MoAb 35F5. In contrast, IL-1 alpha directly synergized with CSF-1 and GM-CSF to promote progenitor cell growth. The direct synergistic effect of IL-1 alpha on CSF-1-induced progenitor growth was observed in all progenitor populations examined (Lin-, Lin-Thy-1+, and Lin-Thy-1-) and was inhibited by MoAb 35F5. However, the direct synergistic effect of IL-1 alpha on GM-CSF-responsive progenitors. Lin- and Lin-Thy-1+, was partially inhibited by MoAb 35F5. In contrast, the MoAb antitype II IL-1R (MoAb 4E2) could not inhibit the direct synergistic effects of IL-1 alpha on CSF-1- or GM-CSF-induced progenitor growth. Thus, IL-1 alpha directly and indirectly stimulates the growth and differentiation of purified progenitors through the type I IL-1R but not the type II IL-1R.

Animals↗

PubMed1994

Hck expression correlates with granulocyte-macrophage colony-stimulating factor-induced proliferation in HL-60 cells.

The human myeloid cell line HL-60 expresses approximately 300 high-affinity granulocyte-macrophage colony-stimulating factor receptors (GM-CSFRs), yet treatment of these cells with GM-CSF does not result in enhanced cellular proliferation or increases in protein tyrosine phosphorylation. In contrast, GM-CSF induces rapid increases in protein tyrosine phosphorylation and proliferative responses in HL-60 cells pretreated for 3 days in dimethyl sulfoxide (DMSO). Similarly, HL-60 cells pretreated with retinoic acid or 1,25 dihydroxyvitamin D3 were also capable of responding to GM-CSF. Interestingly, each of these treatments resulted in increased expression of the src-like tyrosine kinase hck. Stimulation with GM-CSF increased hck autophosphorylation in DMSO-treated HL-60 cells, suggesting that hck is a component of the GM-CSF signal transduction pathway. To determine if hck has a role in the DMSO-induced recoupling of the GM-CSFR, we overexpressed hck in HL-60 cells. The resulting cell line (HL-60/hck) expresses hck mRNA and protein at levels comparable with DMSO-treated HL-60 cells. Stimulation of HL-60/hck cells with GM-CSF results in activation of hck, increases in protein tyrosine phosphorylation, and increased proliferation. These results show that cytokine receptors can exist in an uncoupled form and suggest that in HL-60 cells, appropriate levels of the src-like tyrosine kinase hck are critical for functional coupling of the GM-CSFR to biologic responses.

Cell Division↗

PubMed1994

The gamma subunit of the interleukin-2 receptor is expressed in human monocytes and modulated by interleukin-2, interferon gamma, and transforming growth factor beta 1.

The interleukin-2 receptor gamma (IL-2R gamma) chain is a newly recognized component of the IL-2R of lymphoid cells that is required for their response to IL-2. We investigated the expression of IL-2R gamma protein in human monocytes by Western blot analysis using an antiserum specific for IL-2R gamma. We found that IL-2R gamma subunit is constitutively expressed in human monocytes and upregulated by the monocyte-activating factors IL-2 and interferon gamma (IFN gamma). Furthermore, we show that transforming growth factor beta 1 (TGF beta 1) downmodulates, in a dose-dependent manner, basal and IL-2-induced, but not IFN gamma-induced, IL-2R gamma chain expression, and this effect may be responsible for TGF beta 1 suppressive activity on IL-2-activated monocytes. Overall, these results show that the expression of the IL-2R gamma subunit in human monocytes is tightly regulated by the cytokine network, suggesting a critical role played by this protein on monocyte activation.

Dose-Response Relationship, Drug↗

PubMed1994

Alterations in NF kappa B/Rel family proteins in splenic T-cells from tumor-bearing mice and reversal following therapy.

It has recently been shown that T-cell signal transduction molecules are altered in tumor-bearing mice. We have examined the expression of NF kappa B/Rel family proteins in T-cells from mice bearing Renca, a murine renal carcinoma. T-cells from Renca-bearing mice expressed undetectable levels of nuclear c-Rel, NF kappa B p65, and p50; however, two shorter forms of p50 (p48 and p46), truncated at the NH2-terminus, were present exclusively in the nucleus and were able to bind DNA. These T-cells have reduced expression of gamma-interferon mRNA. In mice successfully treated with flavone 8-acetic acid and recombinant human interleukin 2, the T-cells expressed normal levels of all three nuclear NF kappa B/Rel proteins. These results suggest that alterations in transcription factors may accompany changes in signal transduction molecules in T-cells from tumor-bearing animals; however, the changes are reversed with successful biological therapy.

Animals↗

PubMed1994

Inhibitory cytokine circuits involving transforming growth factor-beta, interferon-gamma, and interleukin-2 in human monocyte activation.

We have previously reported that transforming growth factor-beta 1 (TGF-beta 1) inhibits interleukin-6 (IL-6) induction by IL-2 and IL-1 in fresh human monocytes. We investigated the effects of TGF-beta 1 on the expression of tumoricidal activity induced by IL-2 or interferon-gamma (IFN-gamma) in human monocytes. We showed that TGF-beta 1 specifically inhibited, in a dose-dependent manner, IL-2-induced but not IFN-gamma-induced monocyte tumoricidal activity. The inhibitory effects of TGF-beta 1 on IL-2-activated monocytes were not caused by down-modulation of the IL-2 receptor beta (IL-2R beta) because the treatment of monocytes with IL-2 and TGF-beta 1 increased IL-2R beta mRNA expression. However, we found that TGF-beta 1 down-modulated IL-2-induced IL-2R gamma mRNA, which may be responsible for the TGF-beta 1 inhibition of monocyte activation by IL-2. The resistance of the IFN-gamma-induced activation to the inhibitory effects of TGF-beta 1 could be caused by the ability of IFN-gamma to decrease TGF-beta 1 receptor expression, as shown by cross-linking experiments. Overall, these results showed that TGF-beta 1 is a powerful inhibitor of IL-2- but not of IFN-gamma-induced activation of monocytes to a cytotoxic stage. This differential effect may be attributed to modulation of cytokine receptor expression.

Cells, Cultured↗

PubMed1994

Inhibition of human B-cell lymphoma growth by CD40 stimulation.

CD40 is a molecule present on B lymphocyte lineage cells that is important in B-cell differentiation and activation. Signaling through CD40 has been shown to exert costimulatory signals on normal B cells resulting in proliferative and differentiation responses. Examination of several B-cell lymphomas showed cell-surface expression of the CD40 molecule. Incubation of these lymphomas with anti-CD40 antibodies resulted in significant growth inhibition in vitro. Cross-linking of the CD40 antibodies resulted in even greater inhibition of proliferation. A recombinant soluble human CD40 ligand was also shown to inhibit lymphoma proliferation. When various human B-cell lymphomas were transferred into mice with severe combined immune deficiency, the treatment of the mice with anti-CD40 antibodies resulted in significant increases in survival showing that anti-CD40 is efficacious after in vivo administration. Thus, CD40 stimulation by either the antibody or soluble ligand directly inhibits human B-cell lymphoma growth and therefore, may be of significant clinical use in their treatment.

Animals↗

PubMed1994

B cells from M167 mu kappa transgenic mice fail to proliferate after stimulation with soluble anti-Ig antibodies. A model for antigen-induced B cell anergy.

The transgenic (TG) mouse strain 207-4, carries mu a + kappa transgenes ligated to the anti-phosphocholine (PC) VH1 and V kappa 24 V region genes from the MOPC-167 myeloma. Although B cells from mice carrying these transgenes respond both in vivo and in vitro to thymus-dependent Ags, they failed to proliferate in response to soluble goat anti-mu Ab or other soluble anti-Ig reagents. On the other hand, B cells from the Sp6 mu kappa anti-trinitrophenyl TG mouse line proliferated normally after stimulation with soluble anti-mu. However, the 207-4 anti-PC transgene positive (TG+) splenic B cells proliferated when stimulated with anti-mu, anti-idiotype, anti-allotype, or PC-conjugated to Sepharose beads. TG+ B cells were also induced to proliferate when stimulated with anti-Lyb-2; thus, their defect may be restricted to signaling through sigM. The lack of response to soluble anti-mu could not be reversed by addition of IL-4, by removal of T cells, by addition of anti-FcR Ab, or by stimulation with F(ab')2 anti-mu. Thus, the failure to proliferate was not caused by active T cell suppression or FcR-mediated inhibition. In mixed cultures of TG+ and transgene negative (TG-) spleen cells, the TG- cells were able to proliferate normally to soluble anti-mu, indicating that suppressive factors were not involved in the unresponsiveness of the TG+ anti-PC-specific B cells. These studies suggest that B cells in the 207-4 anti-PC TG mice exhibit a defect in activation through their sIgM receptors, and this unresponsiveness may reflect a form of Ag-induced tolerance.

Animals↗

PubMed1994

Regulation by interleukin-2 (IL-2) and interferon gamma of IL-2 receptor gamma chain gene expression in human monocytes.

The interleukin-2 receptor gamma chain (IL-2R gamma) gene codes for a subunit of the IL-2R and is expressed in human lymphoid cells. The present study was undertaken to determine whether human monocytes expressed the IL-2R gamma gene constitutively or after activation by IL-2 or interferon gamma (IFN gamma). Fresh human monocytes constitutively expressed low but significant levels of IL-2R gamma mRNA, and nuclear run-on experiments showed that IL-2R gamma gene was transcriptionally active. Stimulation with IL-2 or IFN gamma induced a major increase of IL-2R gamma mRNA in a time- and a dose-dependent manner. However, neither cytokine increased the transcriptional activity of the gene. The enhancement of IL-2R gamma mRNA expression by either IL-2 or IFN gamma was concomitant with the stabilization of the mRNA, suggesting a postranscriptional level of control. Finally, the augmented expression of IL-2R gamma in IL-2- and IFN gamma-treated monocytes was associated with an increased IL-2-binding activity, compared with that of unstimulated cells. These results provide the first evidence of the expression of the IL-2R gamma gene in nonlymphoid cells and of its modulation by IL-2 and IFN gamma through posttranscriptional mechanisms.

Flow Cytometry↗

PubMed1994

c-erbB-2 promoter-specific DNA-binding protein isolated from human breast cancer tissues displays mitogenic activity.

Amplification and overexpression of the c-erbB-2 gene appears to play a role in the pathogenesis of human breast and other cancers. Frequent amplification (20-30%) of the c-erbB-2 gene was observed in human adenocarcinomas of kidney, pancreas, lung, ovarian, and breast cancer. The gene product is a 185-kDa glycoprotein that has intrinsic tyrosine kinase activity and is believed to be a receptor. Several candidate ligands have been described. In the present study we have identified and purified a novel DNA-binding protein from malignant human breast tissues. The protein binds to a core element (-22 to +9, +1 being the transcription start site) of the c-erbB-2 promoter region in a sequence-specific manner. The affinity-purified protein has the ability to induce DNA synthesis in quiescent NIH/3T3 cells, suggesting that the factor has mitogenic activity. The purified protein induces c-erbB-2 expression on the surface of microinjected NIH/3T3 cells. This DNA-binding protein is a sequence-specific cellular factor that is associated with high level expression of the c-erbB-2 gene and appears to play a role in cell transformation. Understanding the control and expression of this DNA-binding protein may shed light on the mechanism(s) of c-erbB-2 gene regulation and its potential role in the pathogenesis of human adenocarcinomas.

3T3 Cells↗

PubMed1994

Interleukin-4 inhibits indoleamine 2,3-dioxygenase expression in human monocytes.

Indoleamine 2,3-dioxygenase (IDO), a flavin-dependent enzyme that catalyzes the conversion of tryptophan to kynurenine, is induced in peripheral blood mononuclear cells by interferon-gamma (IFN gamma). Interleukin-4 (IL-4) is a cytokine that modulates the functional properties of monocytes/macrophages, and we investigated the effects of IL-4 on IDO. We showed that IL-4 inhibited the induction of IDO mRNA and IDO activity by IFN gamma in human monocytes. The inhibitory effect was evident with as little as 2 U/mL of IL-4. These results provide the first evidence that a cytokine can provide a negative signal for IDO expression and that IL-4 can influence the catabolism of tryptophan.

Base Sequence↗

PubMed1994

Increased proliferation, cytotoxicity, and gene expression after stimulation of human peripheral blood T lymphocytes through a surface ganglioside (GD3)

Previous studies have suggested that gangliosides have an important role in cell signaling and recognition. However, their specific function in these processes has not been clearly defined. A mAb, R24, that reacts specifically with a cell surface ganglioside (GD3) has been demonstrated to stimulate proliferation of T cells derived from human peripheral blood. In this study, we have investigated the mechanisms by which the R24 mAb affects T cell functions. We have observed that the R24 mAb stimulates GD3+ T cell proliferation, cytotoxicity, and surface marker expression of IL-2R alpha-chain, IL-2R beta-chain, HLA-DR, CD11a, and CD11c. Additionally, IFN-gamma activity but not IL-1, IL-2, or IL-4 activity was present in culture supernatants 72 h after R24 stimulation. In some donors, increased IL-6 and TNF-alpha activity also was detected after R24 treatment. Furthermore, R24 treatment resulted in translocation of c-rel, but little or no NF kappa B p50 or p65, from the cytoplasm to the nucleus and an increase of NF kappa B binding complexes containing c-rel and p50. This treatment also caused increased tyrosine phosphorylation of specific protein substrates. R24-stimulated increases in proliferation, cytotoxicity, and cell surface protein expression could be blocked by cyclosporin and staurosporin, indicating that cyclophilin/calcineurin and protein kinase C may be involved in the R24 signaling pathway. Additionally, herbimycin A, a tyrosine kinase inhibitor, blocked the R24-stimulated increase in proliferation but not cytotoxicity at concentrations consistent with specificity for tyrosine kinases. These results suggest that multiple biochemical pathways are involved in the activation of human T cells by R24.

Amino Acid Isomerases↗

PubMed1994

Interferon-gamma upregulates interleukin-8 gene expression in human monocytic cells by a posttranscriptional mechanism.

Interleukin-8 (IL-8) is a neutrophil chemotactic and activating cytokine that is produced in response to several stimuli. Because monocytic cells are important producers of IL-8, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of activation and differentiation of mononuclear phagocytes, affected IL-8 expression in this cell lineage. We found a low constitutive level of IL-8 mRNA expression that was upregulated by IFN-gamma in a dose- and time-dependent manner and via a protein-synthesis-dependent process in the human monocytic cell line U937. IL-8 protein secretion was also stimulated by IFN-gamma. Nuclear run-on experiments showed that the IL-8 gene was transcriptionally active in control cells and that IFN-gamma did not enhance the transcriptional activity. The increase in IL-8 mRNA by IFN-gamma was concomitant with the stabilization of the mRNA and, therefore, controlled primarily at a posttranscriptional level. These results represent the first evidence that IFN-gamma upregulates IL-8 gene expression in cells of the monocytic lineage, and show the involvement of posttranscriptional mechanisms in the induction of IL-8 mRNA.

Cell Line↗

PubMed1994

Human RANTES induces the migration of human T lymphocytes into the peripheral tissues of mice with severe combined immune deficiency.

The human cytokine, Recombinant Human Regulated on Activation, Normal T Expressed and Secreted (rhRANTES), is a small glycoprotein secreted by activated T cells and platelets and is structurally related to a family of chemotactic cytokines called chemokines. Evaluation of the effects of chemokines on human cells has largely been limited to in vitro binding assays. In an effort to study the in vivo effects of chemokines on human leukocyte migration, we examined the ability of rhRANTES to induce human T cell infiltration using a human/severe combined immune deficient (SCID) mouse model. SCID mice received human peripheral blood lymphocytes, followed by sequential subcutaneous injections of rhRANTES in the hind flank for 3 days. The skin and underlying tissue from the rhRANTES injection site were then biopsied and examined for the extent of human mononuclear cell infiltration. rhRANTES induced significant mononuclear cell accumulation 72 h after injection. Immunohistological evaluation determined that the majority of the cells recruited in response to rhRANTES injections were human CD3+ T cells with equal numbers of CD4+ and CD8+ cells. In contrast, subcutaneous injections of recombinant human macrophage colony-stimulating factors resulted in little human cellular infiltration. Murine mononuclear cell infiltration in response to rhRANTES was also present suggesting that the in vivo effects of rhRANTES may be both direct and indirect. These results demonstrate that rhRANTES induces significant human T cell migration in vivo and suggests that the human/SCID mouse model may provide an important tool in studying the in vivo effects of chemokines on human leukocytes and leukocyte subsets.

Animals↗

PubMed1994

Staurosporine restores signaling and inhibits interleukin-8-induced chemotactic desensitization.

Interleukin 8 (IL-8) is a chemotactic cytokine (chemokine) that plays a key role in the accumulation and activation of neutrophils at inflammatory sites. In this report we demonstrate that homologous chemotactic desensitization occurs upon pretreatment of neutrophils with IL-8 or N-formyl-methionyl-leucyl-phenylalanine (FMLP) and results in the inhibition of neutrophil chemotaxis upon subsequent challenge with the same ligand. This homologous chemotactic desensitization could be prevented by pretreating the neutrophils with the protein kinase inhibitor staurosporine, indicating that protein kinases may play an essential role. The attenuation of homologous desensitization by staurosporine restored chemotaxis but was not associated with a change in IL-8 receptor expression, affinity or the rate of ligand internalization, indicating that homologous desensitization does not alter ligand-receptor interaction. Using two-dimensional analysis we have shown that IL-8 induced a rapid serine/threonine phosphorylation of a number of neutrophil substrates the most prominent being phosphoprotein 39 (pp39), extracellular signal-related kinase-1, pp55 and pp66. Prior desensitization of neutrophils with IL-8 blocked all subsequent phosphorylation upon rechallenge with IL-8. However, the desensitization was specific for IL-8 since normal phosphorylation of identical substrates was observed in response to FMLP. When neutrophils were pretreated with staurosporine, prior to desensitization, phosphorylation of pp39 was observed upon restimulation with IL-8. Further study revealed that pp55 and pp66 were not phosphorylated in the presence of staurosporine. Thus, homologous desensitization of neutrophils in response to IL-8 does not result from changes in receptor expression, but rather from a staurosporine-sensitive inactivation of subsequent signal transduction. This desensitization is selective since the cells are able to respond to other ligands.

Alkaloids↗