Thrombin induces endothelial type II activation in vitro: IL-1 and TNF-alpha-independent IL-8 secretion and E-selectin expression

In addition to its role in coagulation, thrombin is involved in the inflammatory process by inducing vessel neutrophilic infiltration. Thrombin induces endothelial P-selectin expression and platelet activating factor release, which participate to induce early neutrophil adhesion and activation. We employed HUVEC and now show that thrombin induces the production of the chemokine IL-8 in a time- and dose-dependent fashion. Similarly, thrombin induced E-selectin expression on HUVEC. Both IL-8 secretion and E-selectin expression were preceded by an increase in steady state levels of the respective mRNAs. Thrombin action on HUVEC was inhibited by the specific thrombin inhibitor, hirudin. In addition, these effects of thrombin on HUVEC were mimicked by the 14-amino acid thrombin receptor agonist peptide, which triggers the native thrombin receptor in a similar fashion to thrombin itself. Although IL-1 and TNF-alpha also induce IL-8 and E-selectin, the thrombin effects in these experiments were not mediated by those cytokines, since neither IL-1 receptor antagonist nor anti-TNF-alpha Ab inhibited the effects of thrombin. Furthermore, IL-1alpha, IL-1beta, and TNF-alpha were not detected in the supernatants of thrombin-activated HUVEC. Although intracellular IL-1alpha was found in thrombin-activated HUVEC, antisense IL-1alpha had no inhibitory effect on IL-8 secretion. These results demonstrate that in addition to short term endothelial activation, thrombin also functions as a long acting proinflammatory agent by inducing endothelial synthesis of the mediators required for neutrophils activation and extravazation during inflammation.

Thrombin induces endothelial type II activation in vitro: IL-1 and TNF-alpha-independent IL-8 secretion and E-selectin expression

In addition to its role in coagulation, thrombin is involved in the inflammatory process by inducing vessel neutrophilic infiltration. Thrombin induces endothelial P-selectin expression and platelet activating factor release, which participate to induce early neutrophil adhesion and activation. We employed HUVEC and now show that thrombin induces the production of the chemokine IL-8 in a time- and dose-dependent fashion. Similarly, thrombin induced E-selectin expression on HUVEC. Both IL-8 secretion and E-selectin expression were preceded by an increase in steady state levels of the respective mRNAs. Thrombin action on HUVEC was inhibited by the specific thrombin inhibitor, hirudin. In addition, these effects of thrombin on HUVEC were mimicked by the 14-amino acid thrombin receptor agonist peptide, which triggers the native thrombin receptor in a similar fashion to thrombin itself. Although IL-1 and TNF-alpha also induce IL-8 and E-selectin, the thrombin effects in these experiments were not mediated by those cytokines, since neither IL-1 receptor antagonist nor anti-TNF-alpha Ab inhibited the effects of thrombin. Furthermore, IL-1alpha, IL-1beta, and TNF-alpha were not detected in the supernatants of thrombin-activated HUVEC. Although intracellular IL-1alpha was found in thrombin-activated HUVEC, antisense IL-1alpha had no inhibitory effect on IL-8 secretion. These results demonstrate that in addition to short term endothelial activation, thrombin also functions as a long acting proinflammatory agent by inducing endothelial synthesis of the mediators required for neutrophils activation and extravazation during inflammation.

Leukosialin (CD43) behavior during adhesion of human monocytic THP-1 cells to red blood cells

To understand the modulation and the behavior of glycocalyx elements during adhesion, we explored one of its components, the CD43 molecule, on human monocytic THP-1 cells exposed to cytokine stimulation and its redistribution during heterotypic adhesion to opsonized erythrocytes. First we demonstrated by immunofluorescence and immunoprecipitation that CD43 is dys-sialylated in monocytic THP-1 cells stimulated by interferon-gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) and stimulation increased correlated to heterotypic adhesion. CD43 anti-adhesive effect seemed to be related to sialic acid moeties because an increase in adhesion was also induced by sialidase treatment and by monoclonal antibodies recognizing sialic acid-dependent epitopes on CD43. Second, a redistribution of CD43 molecules was observed after adhesion, resulting in the exclusion of CD43 molecules from contact areas as demonstrated by immunofluorescence and by ultrastructural immunogold localization. We therefore demonstrated in monocytic THP-1 cells that some glycocalyx molecules can be modulated by cytokines and redistributed during adhesion. These results support the concept that CD43 can regulate cell interactions.

The dependence of the association rate of surface-attached adhesion molecules CD2 and CD48 on separation distance

The kinetics of bond formation between spherical beads coated with CD48 and CD2-derivatized surfaces was studied with a flow chamber. For a given shear rate, the binding frequency was exquisitively sensitive to the particle velocity. Flow equations were used to derive the particle-to-surface distance from the velocity, thus yielding a relationship between this distance and the binding rate. Numerical values of the binding site densities allowed absolute determination of the rate of association between two individual molecules as a function of the distance between attachment points. In our model, this rate was about 0.03 s-1 at 10 nm separation, and it was inversely proportional to the cube of the distance.

Determination of the lifetime and force dependence of interactions of single bonds between surface-attached CD2 and CD48 adhesion molecules

We studied single molecular interactions between surface-attached rat CD2, a T-lymphocyte adhesion receptor, and CD48, a CD2 ligand found on antigen-presenting cells. Spherical particles were coated with decreasing densities of CD48-CD4 chimeric molecules then driven along CD2-derivatized glass surfaces under a low hydrodynamic shear rate. Particles exhibited multiple arrests of varying duration. By analyzing the dependence of arrest frequency and duration on the surface density of CD48 sites, it was concluded that (i) arrests were generated by single molecular bonds and (ii) the initial bond dissociation rate was about 7.8 s-1. The force exerted on bonds was increased from about 11 to 22 pN; the detachment rate exhibited a twofold increase. These results agree with and extend studies on the CD2-CD48 interaction by surface plasmon resonance technology, which yielded an affinity constant of approximately 10(4) M-1 and a dissociation rate of > or = 6 s-1. It is concluded that the flow chamber technology can be an useful complement to atomic force microscopy for studying interactions between isolated biomolecules, with a resolution of about 20 ms and sensitivity of a few piconewtons. Further, this technology might be extended to actual cells.

Insulin-induced lipoatrophy in type I diabetes. A possible tumor necrosis factor-alpha-mediated dedifferentiation of adipocytes

OBJECTIVE

To test the hypothesis that tumor necrosis factor (TNF)-alpha may mediate the loss and the dedifferentiation of subcutaneous fat tissue in the insulin-induced lipoatrophies of a diabetic patient who presented extensive lesions.

RESEARCH DESIGN AND METHODS

An in vitro exploration of cytokine production by peripheral blood mononuclear cells (PBMC) from the reported case was performed and compared with the same explorations of PBMC from three nondiabetic subjects and three diabetic patients without lipoatrophic lesions. A proliferation test and an evaluation of TNF-alpha and interleukin (IL)-6 production from PBMC in presence of insulin were studied.

RESULTS

The production of TNF-alpha and IL-6 by the macrophages of the patient in presence of insulin were dramatically increased in comparison with control subjects. This process needed cooperation with other lymphoid cells and was abrogated by dexamethasone.

CONCLUSIONS

In our reported case, a local hyperproduction of TNF-alpha from macrophages that was induced by the injected insulin could explain the dedifferentiation of the adipocytes of the subcutaneous tissue and the reversion that was induced by the local injection of dexamethasone.

Measuring bonds between surface-associated molecules

Adhesive interactions play an essential role in immune function. Much information on these phenomena was recently obtained by applying sophisticated methods such as the surface forces apparatus, atomic force microscopy, lipid vesicle-based technology or flow chambers. In the present review it is shown that the use of hydrodynamic flow allows quantitative study of the formation and dissociation of individual molecular bonds between receptor-bearing cells or particles and ligand-derivatized surfaces. In addition, it should be possible to determine particle-surface interaction forces with subpiconewton sensitivity and nanometer resolution. Data analysis shows that the classical concepts of bond strength, or association and dissociation rates must be reexamined in order to achieve a correct understanding of the behavior of individual molecules.

Adhesive and migratory behaviors of nevus cells differ from those of epidermal melanocytes and are not linked to the histological type of nevus

It has been postulated that acquired nevi undergo life span continuous evolution from junctional, presumably in radial expanding phase at the dermal epidermal junction, to compound and then to dermal nested nevi. In an attempt to correlate the morphology of nevi with biological data, we have investigated whether migratory and adhesive phenotypes of nevus cells could account for histological patterns and possible spatiotemporal changes in nevi. Nevus cells were cultured from compound and dermal nevi and compared to normal epidermal cultured melanocytes from children and adults. AR nevus cells showed similar in vitro adhesive and migratory indexes on laminin-1, laminin-5/nicein, fibronectin, or collagen IV substrates, suggesting that these intrinsic characteristics do not account for the tendency to dermal nesting and/or to radial growth along the dermal-epidermal junction. The cells from epidermal and dermal parts of compound nevi migrated similarly across a reconstituted basement membrane. The results show that intrinsic adhesive and migratory behaviors of nevus cells were not associated with a histological type of nevus. Interestingly, differences in migratory phenotype and intercellular adhesion capacities between nevus cells and normal melanocytes indicated that they could represent different melanocytic cell subpopulations. Finally, melanocytes from adults and children expressed similar levels of the same integrins as all nevus cells but showed differences in function of both alpha3 and alpha6 integrin subunits and in migratory/adhesive behaviors, which may suggest different states of melanocyte maturation.

Balance between alveolar macrophage IL-6 and TGF-beta in lung-transplant recipients. Marseille and Montréal Lung Transplantation Group

Acute inflammation in the lung is characterized by a phase of tissue injury followed by a phase of tissue repair. When the latter is excessive, fibrosis occurs. Alveolar macrophages (AM) can produce cytokines involved in both phases of acute lung inflammation, notably interleukin-6 (IL-6), involved in injury and transforming growth factor-beta (TGF-beta), mediating repair. We hypothesized that AM were activated in both phases, and studied IL-6 and TGF-beta production by AM during complications of lung transplantation, acute rejection (AR), and cytomegalovirus pneumonitis (CMVP). In addition, we analyzed these cytokines in bronchiolitis obliterans (BO), a fibrotic complication of lung transplantation linked to previous AR and CMVP. At the onset of AR and CMVP, IL-6 secretion increased, whereas AM TGF-beta content was increased, but not its secretion. In contrast, with time, IL-6 reached control value whereas TGF-beta secretion rose significantly. In BO, IL-6 was not oversecreted, but TGF-beta increased, notably before functional abnormalities occurred. These results show that during acute complications of lung transplantation, AM display an early activation with oversecretion of IL-6, which is involved in tissue injury, counterbalanced by a late activation in which TGF-beta predominates, mediating tissue repair. The results provide new insights into the pathogenesis of BO, which is linked to acute complications of lung transplantation through this biphasic AM activation.

Use of thermal fluctuations to study the length and flexibility of ligand-receptor bonds

We describe an experimental approach yielding new information on the behavior of ligand-receptor bonds. Spherical particles of 1.4 microns radius were coated with anti-rabbit immunoglobulin monoclonal antibodies and deposited on surfaces derivatized with rabbit immunoglobulins. Brownian motion was studied. When particles where bound through multiple bonds, the mean square displacement during a 1 s interval was 0.0038 micron2 as compared to 0.245 micron2 for unbound particles. Under the same conditions, the mean square displacement of particules coated with limiting dilutions of binding sites and bound by single molecular bonds was 0.0774 micron2. Results are compatible with the concept that the latter particles behaved as spheres transiently bound to the substratum by links of 2.7 nm length, allowing brownian oscillations with an angular amplitude of 0.062 radian.

IL-6 and IL-8 production from cultured human endothelial cells stimulated by infection with Rickettsia conorii via a cell-associated IL-1 alpha-dependent pathway

Mediterranean spotted fever due to infection by Rickettsia conorii, is characterized by a general vasculitis. This vasculitis is thought to be due to a direct injury to endothelial cells induced by R. conorii. However, production and activity of cytokines on endothelial cells is an important pathway in inflammation, and part of the underlying mechanism of vasculitis. In the present studies, human umbilical vein endothelial cells (HUVEC) infected with R. conorii actively secrete high levels of IL-8 and IL-6 (P < 0.002, and P < 0.03, respectively, compared with uninfected cells). IL-1alpha, IL-1beta, or TNFalpha were not detected in the culture supernates. Nevertheless, IL-6 and IL-8 production was due, in a large part, to a cell-associated form of IL-1 alpha expressed on R. conorii-infected HUVEC, since production of these cytokines was suppressed by 80% (P = 0.0001) and 85% (P < 0.04) by the addition of IL-1 receptor antagonist, or anti-IL-1alpha antibodies (60% inhibition, P < 0.01 and 65% inhibition, P < 0.05, respectively) and IL-1alpha was measured after lysis of R. conorii-infected HUVEC but not in uninfected cells (P < 0.01). Rickettsial lipopolysaccharide does not seem to be involved, since polymyxin B did not reduce cytokine secretion. On the contrary, infection by intracellular R. conorii appears to be necessary to induce IL-1alpha and subsequently IL-8, since formalin-fixed R. conorii did not induce cytokine production. These observations demonstrate that R. conorii-infected HUVEC secrete IL-6 and IL-8 via the induction of cell-associated IL-1alpha, providing a possible mechanism for the vasculitis observed in Mediterranean spotted fever.

Measuring the lifetime of bonds made between surface-linked molecules

It is not well known how the kinetic constants of association between soluble receptors and ligands may be used to predict the behavior of these molecules when they are bound to cell surfaces. Spherical beads were coated with varying densities of anti-rabbit immunoglobulin monoclonal antibodies and driven along glass surfaces derivatized with rabbit anti-dinitrophenol. Particle motion was analyzed. The velocity, attachment frequency, and duration of binding events were determined on individual particles. It was found that i) beads exhibited frequent arrests lasting between a few tenths of a second and more than one minute; ii) when antibodies were diluted, the median arrest duration remained fairly constant (approximately 1 s) whereas binding frequency varied as the first power of the antibody concentration, suggesting that most particle arrests were due to the formation of a single bond; iii) when the shear rate was increased 7-fold, the duration of transient binding events remained constant. The disruptive force exerted on attachment points was estimated to range between about 6 and 37 piconewtons; and iv) the distribution of arrest durations suggested that binding was not a monophasic reaction but involved at least one intermediate step. Therefore, transient binding events reflected the formation of unstable associations that are not detected with standard techniques.

Influence of surface charges on cell adhesion: difference between static and dynamic conditions

We tested the hypothesis that nonspecific repulsion, as a result of electrostatic forces and (or) steric stabilization effects, impaired adhesion more efficiently under dynamic than under static conditions. Cells from the human monocytic line THP1 were plated on a glass surface. Spherical particles bearing monoclonal antibodies specific for antigens expressed by THP1 cells (CD11b, CD18, CD35, CD64) were then added and adhesion was quantified. The effect of neuraminidase treatment of THP1 cells was also studied. Adhesion was then measured in a flow chamber under low shear flow (wall shear rate was 11 or 22 s-1), allowing a quantitative determination of cell adhesion frequency. The following conclusions were obtained: (i) under static conditions, neuraminidase treatment had little effect on adhesion (only CD18-mediated interaction was significantly increased at 4 degrees C after enzyme treatment); (ii) under dynamic conditions, neuraminidase treatment significantly increased binding; (iii) surprisingly, there was no clear relationship between the length of adhesion molecules involved in the interaction and binding efficiency; and (iv) such parameters as cell shape and topographical distribution of adhesion molecules may strongly influence adhesion under flow. It is concluded that a dynamic reorganization of the pericellular matrix following intercellular contact may play an important role in regulating adhesion.

Immunocytochemical study of NA+ K(+)-ATPase alpha 1 and beta 1 subunits in human and rat normal hepatocytes using confocal microscopy

Hepatic Na+ K(+)-ATPase was recently shown to be composed of two alpha 1 and beta 1 subunits similar to that of kidney. Its localization on hepatocyte plasma membranes was not clearly established. We have studied the localization of alpha 1 and beta 1 subunits using immunocytochemical method and confocal microscopy. In accordance with previous cytochemical findings, the catalytic alpha 1 subunit was distributed in basolateral and bile canalicular membranes of hepatocytes. The beta 1 subunit was not demonstrated, due to its very low amount in the liver. The controversy about the bile canalicular localization was discussed.

Interleukin-1 induces interleukin-8 secretion from endothelial cells by a juxtacrine mechanism

Inflammation is characterized by migration of neutrophils through the endothelium, and the chemokine interleukin-8 (IL-8) appears to be involved. We asked whether adherence of cells bearing a membrane-form of interleukin 1 (IL-1) induces IL-8 secretion from human umbilical vein endothelial cells (HUVEC) and fibroblasts. Human peripheral blood mononuclear cells (PBMC) were stimulated with endotoxin for 12 hours and then fixed for 4 hours with paraformaldehyde. When these cells were added to HUVEC or fibroblasts, IL-8 production was induced. This stimulation by fixed PBMC was attributed to IL-1, because pretreatment of HUVEC or fibroblasts with IL-1 receptor antagonist (IL-1Ra) reduced the induction by 95% and 80%, respectively, P < .005. Using anti-IL-1 alpha monoclonal antibodies, reduction was complete, whereas anti-IL-1 beta had no effect. IL-1 alpha was shown on the surface of monocytes by fluorescence-activated cell sorter (FACS) analysis. Blockade of IL-1 receptors on PBMC did not affect the activity of membrane-associated IL-1 alpha, indicating that IL-1 is not anchored to the membrane through its receptors. However, PBMC treated with D-mannose before fixation resulted in a loss of activity; this loss of activity was associated with release of IL-1 alpha, not IL-1 beta, into the supernatant. Thus, anchoring of IL-1 alpha to the membrane may be via a lectin or mannose receptor-like interaction. Blockade of membrane IL-1 alpha required a 30-fold and fivefold excess of IL-1Ra compared with the amount required to block soluble IL-1 beta and IL-1 alpha, respectively. We conclude that the fixed PBMC IL-8 inducing activity is almost entirely caused by IL-1, that this represents IL-1 alpha bound to a surface lectin or mannose receptor on the monocyte, and that it functions in inflammation via juxtacrine interactions.

A novel role for E- and P-selectins: shape control of endothelial cell monolayers

The migration of neutrophils from blood vessels to peripheral tissues is a key step of inflammation. This requires the formation of transient gaps between endothelial cells with concomitant leucocyte squeezing through these narrow apertures and immediate restoration of endothelium continuity. It is currently considered that the main role of selectins is to mediate the initial contact between flowing leucocytes and endothelial cells. We show here that the binding of E- or P-selectins by specific antibodies induces a marked ‘rounding up’ of interleukin-1- or thrombin-activated human endothelial cells, respectively. Also, anti-E-selectin antibodies trigger a transient increase in cytosolic calcium involving intracellular calcium stores. No such effect is observed when von Willebrand factor or intercellular adhesion molecule 1 are similarly bound. Thus, in addition to promoting the initial interaction between activated endothelium and moving leucocytes, selectins might play a role in the induction of subsequent endothelial deformation, which would facilitate leucocyte arrest and transmigration towards peripheral tissues, and enhance the diffusion of soluble molecules between intravascular and peripheral compartments. Our results are consistent with this hypothesis and demonstrate a new property of endothelial selectins.

Monitoring of alveolar macrophage production of tumor necrosis factor-alpha and interleukin-6 in lung transplant recipients. Marseille and Montreal Lung Transplantation Group

Bronchiolitis obliterans (BO), a common complication in lung transplant recipients, is a fibrotic process probably related to acute rejection (AR) and cytomegalovirus pneumonitis (CMVP). Because the pathogenesis of pulmonary fibrotic diseases involves activation of alveolar macrophages (AM), the present study was carried out to determine if AM were activated during AR, CMVP, and BO. Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were measured in 157 AM supernatants obtained from 29 transplant recipients by immunoradiometric assay. Five groups were analyzed: AR (n = 21), CMVP (n = 12), BO (n = 15), bacterial pneumonia (BP) (n = 8), and control subjects (n = 70). Cytokines were also assayed 15 d (n = 15) and 30 d (n = 9) after AR and 30 d (n = 9) after CMVP. Cytokine secretion was elevated during AR (TNF-alpha = 3,709 +/- 1,409 pg/10(6) cells, IL-6 = 5,482 +/- 2,058 pg/10(6) cells, p < 0.005), and they returned to control values within 15 d. A similar pattern was observed during CMVP (TNF-alpha = 5,000 +/- 2,773 pg/10(6) cells, IL-6 = 12,280 +/- 3,939 pg/10(6) cells, p < 0.005), and values returned to control levels within 30 d. During BP, cytokine production values were higher than control values, but to a lesser extent than in AR and CMVP (TNF-alpha = 2,502 +/- 1,072, p < 0.05; IL-6 = 3,734 +/- 1,440, p < 0.005). In contrast, cytokine secretion during BO was not statistically different from that of control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Histoenzymatic study of human renal tissue preservation: II--Catalase activity in proximal tubular cells is uncorrelated with transplant evolution

Enzyme histochemical activity of catalase, a peroxisomal enzyme involved in cellular antioxidant systems, was studied in proximal tubular cells of human renal transplants as a marker of ischemia-reperfusion injury in the prediction of the evolution of renal transplants. A low enzymatic activity was observed in all renal biopsies performed at 30 min. reperfusion with no difference between the several evolution types of renal transplants. Reduced catalase activity due to ischemia-reperfusion injury could not be correlated with renal function or used as an index of renal function recovery.

Relationship between phagosome acidification, phagosome-lysosome fusion, and mechanism of particle ingestion

The fate of pathogens ingested by macrophages is dependent on phagosome acidification and fusion with different intracellular vesicles. Whereas the mode of particle recognition by the phagocyte seems the main determinant of phagosome-lysosome fusion, the influence of membrane reorganization, fusion events, and cell activation in phagosome acidification is not well known. We looked for a relationship between the nature of receptors involved in phagocytosis, phagosome acidification, and phagosome-lysosome fusion. Murine macrophage-like P388D1 cells were made to ingest sheep erythrocytes coated with immunoglobulin G (EIgG) or IgM and complement (EIgMC) or treated with glutaraldehyde and periodate (EGP). The following results were obtained: (1) As expected, the adhesion of the three particle types was differentially inhibited by monoclonal antibodies specific for Fc gamma RII and CD11b/CD18. (2) The phagosomes containing all three particle types displayed similar acidification kinetics with a pH decrease to 6 within the first 10 min after ingestion. (3) Only phagosomes containing EIgG or EIgMC were fused with peroxidase-loaded secondary lysosomes. (4) Coating EGP with IgG only partially restored fusion, even when the surface density of IgG was markedly higher than found on EIgG. It is concluded that phagosome acidification and fusion are regulated by different mechanisms. Also, the lack of fusion observed with EGP is not entirely accounted for by the absence of stimulation of suitable receptors on the phagocyte membrane, because it cannot be restored by providing such a stimulus.

Dynamic adhesion of CD8-positive cells to antibody-coated surfaces: the initial step is independent of microfilaments and intracellular domains of cell-binding molecules

Cell adhesion is a multistep, metabolically active process usually requiring several minutes or even hours to complete. This results in the formation of strong bonds that cannot be ruptured by mechanical forces encountered by living cells in their natural environment. However, the first seconds after contact formation are much more sensitive to external conditions and may be the critical step of adhesion. This step is very difficult to monitor without disturbing the observed system. We addressed this problem by studying the interaction between anti-CD8-coated or control surfaces and murine lymphoid cell lines bearing wild-type CD8 molecules, or genetically engineered molecules bearing extracellular CD8 domains and transmembranar and intracytoplasmic domains of class I histocompatibility molecules, or with extensive deletion of intracytoplasmic domains. We used a new method that consisted of monitoring the motion of cells driven along adhesive surfaces by a hydrodynamic force weaker than the reported strength of single ligand-receptor bonds, but sufficient to make free cells move with an easily detectable velocity of several micrometers per second. Cells exhibited short-term (< or = 0.5 s) adhesions to the surface with a frequency of about one event per 30-s period of contact. These events did not require specific antigen-antibody bonds. However, when anti-CD8 were present, strong adhesion was achieved within < 1 s, since most arrests were longer than a standard observation period of 1 min. This bond strengthening was not affected by cytochalasin, and it did not require intact intracellular domains on binding molecules. It is concluded that the initial step in strong adhesion may be viewed as a passive, diffusion-driven formation of a new specific bonds.

Protein tyrosine kinases and TNF alpha secretion in human monocytes

The role of protein tyrosine kinases (PTK) in TNF alpha secretion by human monocytes was investigated in this report. We showed that an immunomodulator such as Nocardia lysozyme digest (NLD) and a particulate agonist, zymosan, stimulated an increase in tyrosine phosphorylation of several endogenous substrates including 53-56 kDa protein which was the predominant phosphoprotein. In addition, NLD and zymosan induced TNF alpha secretion which was impaired by a PTK inhibitor, tyrphostin. We suggest that a cascade of kinases including PTK is involved in NLD and zymosan signalling.