Cannabinoids as therapeutic agents for ablating neuroinflammatory disease.

Cannabinoids have been reported to alter the activities of immune cells in vitro and in vivo. These compounds may serve as ideal agents for adjunct treatment of pathological processes that have a neuroinflammatory component. As highly lipophilic molecules, they readily access the brain. Furthermore, they have relatively low toxicity and can be engineered to selectively target cannabinoid receptors. To date, two cannabinoid receptors have been identified, characterized and designated CB(1) and CB(2). CB(1) appears to be constitutively expressed within the CNS while CB(2) apparently is induced during inflammation. The inducible nature of expression of CB(2) extends to microglia, the resident macrophages of the brain that play a critical role during early stages of inflammation in that compartment. Thus, the cannabinoid-cannabinoid receptor system may prove therapeutically manageable in ablating neuropathogenic disorders such as Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, HIV encephalitis, closed head injury, and granulomatous amebic encephalitis.

CB2 receptors in the brain: role in central immune function.

Recently, it has been recognized that the cannabinoid receptor CB2 may play a functionally relevant role in the central nervous system (CNS). This role is mediated primarily through microglia, a resident population of cells in the CNS that is morphologically, phenotypically, and functionally related to macrophages. These cells also express the cannabinoid receptor CB1. The CB1 receptor (CB1R) is constitutively expressed at low levels while the CB2 receptor (CB2R) is expressed at higher levels and is modulated in relation to cell activation state. The relatively high levels of the CB2R correspond with microglia being in 'responsive' and 'primed' states, suggesting the existence of a 'window' of functional relevance during which activation of the CB2R modulates microglial activities. Signature activities of 'responsive' and 'primed' microglia are chemotaxis and antigen processing, respectively. The endocannabinoid 2-arachidonylglycerol has been reported to stimulate a chemotactic response from these cells through the CB2R. In contrast, we have shown in vivo and in vitro that the exogenous cannabinoids delta-9-tetrahydrocannabinol and CP55940 inhibit the chemotactic response of microglia to Acanthamoeba culbertsoni, an opportunistic pathogen that is the causative agent of Granulomatous Amoebic Encephalitis, through activation of the CB2R. It is postulated that these exogenous cannabinoids superimpose an inhibitory effect on pro-chemotactic endocannabinoids that are elicited in response to Acanthamoeba. Furthermore, the collective results suggest that the CB2R plays a critical immune functional role in the CNS.

The interaction between the amoeba Balamuthia mandrillaris and extracellular matrix glycoproteins in vitro.

Balamuthia mandrillaris, a soil amoeba, is the causative agent of Balamuthia granulomatous amoebic encephalitis, a life-threatening brain infection. This amoeba is acquired from contaminated soil and may enter the host through cutaneous lesions or through nasal passages, migrating to the lungs or brain. During invasion, B. mandrillaris has access to components of the extracellular matrix (ECM) of the host. Therefore, we investigated the interaction of B. mandrillaris with 3 ECM glycoproteins (collagen-I, fibronectin and laminin-1) that are encountered in host connective tissues and at the basal lamina. Using optical microscopy, amoeba association on ECM-coated surfaces was examined. Binding of amoebae on laminin was greater than that on collagen or fibronectin. Laminin-adhered B. mandrillaris exhibited elongated and spread forms, distinctive from those observed for amoebae on a plastic surface. Collagen and fibronectin-adhered B. mandrillaris presented elongated shapes with cellular expansions. Binding to collagen, fibronectin, or laminin was inhibited when amoebae were pre-treated with sialic acid. Treatment with galactose resulted in diminished binding of amoebae on laminin, while mannose increased binding in all coating conditions tested. Dependence of divalent cations on amoeba binding was demonstrated for laminin-amoeba interaction. Collectively, the results indicate that B. mandrillaris recognizes specific glycoproteins of the mammalian extracellular matrix.

Cannabinoid receptors in microglia of the central nervous system: immune functional relevance.

Microglia, resident macrophages of the brain, function as immune effector and accessory cells. Paradoxically, they not only play a role in host defense and tissue repair but also have been implicated in a variety of neuropathological processes. Microglia, in addition to exhibiting phenotypic markers for macrophages, express CB1 and CB2 cannabinoid receptors. Recent studies suggest the existence of a third, yet-to-be cloned, non-CB1, non-CB2 cannabinoid receptor. These receptors appear to be functionally relevant within defined windows of microglial activation state and have been implicated as linked to cannabinoid modulation of chemokine and cytokine expression. The recognition that microglia express cannabinoid receptors and that their activation results in modulation of select cellular activities suggests that they may be amenable to therapeutic manipulation for ablating untoward inflammatory responses in the central nervous system.

Effects on the immune system.

Marijuana and other exogenous cannabinoids alter immune function and decrease host resistance to microbial infections in experimental animal models and in vitro. Two modes of action by which delta9-tetrahydrocannabinol (THC) and other cannabinoids affect immune responses have been proposed. First, cannabinoids may signal through the cannabinoid receptors CB1 and CB2. Second, at sites of direct exposure to high concentrations of cannabinoids, such as the lung, membrane perturbation may be involved. In addition, endogenous cannabinoids or endocannabinoids have been identified and have been proposed as native modulators of immune functions through cannabinoid receptors. Exogenously introduced cannabinoids may disturb this homoeostatic immune balance. A mode by which cannabinoids may affect immune responses and host resistance maybe by perturbing the balance of T helper (Th)1 pro-inflammatory versus Th2 anti-inflammatory cytokines. While marijuana and various cannabinoids have been documented to alter immune functions in vitro and in experimental animals, no controlled longitudinal epidemiological studies have yet definitively correlated immunosuppressive effects with increased incidence of infections or immune disorders in humans. However, cannabinoids by virtue of their immunomodulatory properties have the potential to serve as therapeutic agents for ablation of untoward immune responses.

Differential expression of the CB2 cannabinoid receptor by rodent macrophages and macrophage-like cells in relation to cell activation.

An in vitro model of multi-step activation, in which cells of macrophage lineage are driven sequentially through inflammatory, primed, and fully activated states, was employed to assess for cannabinoid receptor expression. Murine and rat peritoneal macrophages, murine RAW264.7 and P388D, macrophage-like cells, and neonatal rat brain cortex microglia expressed the cannabinoid receptor type 2 (CB2) differentially in relation to cell activation. The CB2 was undetectable in resident peritoneal macrophages, present at high levels in thioglycolate-elicited inflammatory and interferon gamma (IFNgamma)-primed peritoneal macrophages, and detected at significantly diminished levels in bacterial lipopolysaccharide (LPS)-activated peritoneal macrophages. A comparable pattern of differential expression of the CB2 was noted for murine macrophage-like cells and neonatal rat brain cortex microglia. The cannabinoid receptor type 1 (CB1) was not detected in peritoneal macrophages or murine macrophage-like cells regardless of cell activation state but was present in neonatal rat microglia at low levels. These results indicate that levels of the CB2 in cells of macrophage lineage undergo major modulatory changes in relation to cell activation. Furthermore, since inflammatory and primed macrophages express the highest levels of CB2, the functional activities of macrophages when in these respective states of activation may be the most sensitive to the action of cannabinoids.

Cannabinoid-mediated inhibition of inducible nitric oxide production by rat microglial cells: evidence for CB1 receptor participation.

Activated brain microglial cells release inflammatory mediators such as nitric oxide (NO) that may play important roles in central nervous system antibacterial, antiviral, and antitumor activities. However, excessive release of these factors has been postulated to elicit immune-mediated neurodegenerative inflammatory processes and to cause brain injury. Recent studies using the rat animal model indicate that select cannabinoids may modulate production of these inflammatory factors. Treatment of neonatal rat brain cortical microglial cells with the cannabinoid paired enantiomers CP55940 and CP56667 resulted in a stereoselective differential effect on inducible NO production. The analog CP55940 exerted a dose-dependent inhibition of interferon gamma (IFNy)/bacterial lipopolysaccharide (LPS)-inducible NO production which was significantly greater than that exerted by CP56667. Pretreatment of microglial cells with the CB1 cannabinoid receptor-selective antagonist SR141716A reversed this CP55940-mediated inhibition. MRT-PCR demonstrated the presence of CB1 receptor mRNA within microglial cells consistent with the presence of CB1 receptors. Collectively, these results indicate that the cannabinoid analog CP55940 selectively inhibits inducible NO production by microglial cells and that this inhibition is effected, at least in part, through the CB1 receptor.

Delta(9)-tetrahydrocannabinol selectively increases aspartyl cathepsin D proteolytic activity and impairs lysozyme processing by macrophages.

Delta(9)-tetrahydrocannabinol (THC) causes an antigen-dependent defect in the ability of macrophages to activate helper T cells, and this drug-induced impairment is mediated through the peripheral CB2 receptor. Various requirements for the processing of the antigen, lysozyme, were examined to determine where along the pathway THC exerts its influence. A THC-exposed macrophage hybridoma inefficiently stimulated interleukin-2 secretion by a helper T cell hybridoma in response to native lysozyme and its reduced form, suggesting that disulfide bond reduction was unaffected. Cell surface expression of major histocompatibility complex class II molecules was normal on THC-exposed macrophages. The drug-exposed macrophages also competently presented a lysozyme peptide to the T cells, indicating that the class II molecules were functional. The proteolytic activity of two thiol cathepsins was unaltered, but aspartyl cathepsin D activity was significantly increased in THC-exposed macrophages. Thus, selective up-regulation of aspartyl cathepsin activity accompanied the deficiency in lysozyme processing and may contribute, at least in part, to the antigen-dependent processing defect in THC-exposed macrophages.

The increasing importance of Acanthamoeba infections.

Free-living amebae belonging to the genus Acanthamoeba are the causative agents of granulomatous amebic encephalitis, a chronic progressive disease of the central nervous system, and of amebic keratitis, a chronic eye infection. Granulomatous amebic encephalitis occurs more frequently in immunocompromised patients while keratitis occurs in healthy individuals. The recent increased incidence in Acanthamoeba infections is due in part to infection in patients with acquired immune deficiency syndrome, while that for keratitis is due to the increased use of contact lenses. Understanding the mechanism of host resistance to Acanthamoeba is essential since the amebae are resistant to many therapeutic agents. Studies in our laboratory as well as from others have demonstrated that macrophages from immunocompetent animals are important effector cells against Acanthamoeba. We have demonstrated also that microglial cells, resident macrophages of the brain, elicit cytokines in response to A. castellanii. Neonatal rat cortical microglia from Sprague-Dawley rats co-cultured with A. castellanii produced mRNA for the inflammatory cytokines, interleukin 1alpha, interleukin 1beta, and tumor necrosis factor alpha. In addition, scanning and transmission electron microscopy revealed that microglia ingested and destroyed A. castellanii in vitro. These results implicate macrophages as playing an effector role against Acanthamoeba and suggest immune modulation as a potential alternative therapeutic mode of treatment for these infections.

Cannabinoids inhibit LPS-inducible cytokine mRNA expression in rat microglial cells.

The effect of cannabinoids on the induction of cytokine mRNA by rat microglial cells was examined. Exposure of neonatal rat cortical microglial cells to the exogenous cannabinoid delta(9)-tetrahydrocannabinol (THC) resulted in reduced amounts of lipopolysaccharide (LPS)-induced mRNAs for IL-1alpha, IL-1beta, IL-6, and TNF-alpha. Of these cytokine mRNAs, the response of that for IL-6 was exquisitely sensitive to THC. Similarly, exposure of microglial cells to the putative endogenous cannabinoid anandamide before LPS treatment resulted in a decrease in cytokine mRNA levels, but not to the same extent as that caused by THC; however, when methanandamide, the non-hydrolyzable analog of anandamide was tested, its ability to inhibit cytokine mRNA expression was comparable to that of THC. Exposure of microglial cells to either of the paired enantiomers CP55,940 or CP56,667 resulted in similar inhibition of LPS-induced cytokine mRNA expression. A comparable inhibitory outcome was obtained when the paired enantiomers levonantradol and dextronantradol were employed. Neither the CB(1)-selective antagonist SR141716A nor the CB(2)-selective antagonist SR144528 was able to reverse the inhibition of cytokine mRNA expression by levonantradol. The CB(2) antagonist, however, when administered alone augmented the production of cytokine mRNAs. Collectively, these studies demonstrate that cannabinoids can modulate levels of cytokine mRNA in rat microglial cells; however, the inhibition of cytokine mRNA expression is apparently not mediated through either the CB(1) or CB(2) cannabinoid receptors.

Cannabinoid inhibition of the processing of intact lysozyme by macrophages: evidence for CB2 receptor participation.

Delta9-tetrahydrocannabinol (THC) impairs multiple immunological functions. The ability of a macrophage hybridoma to function as an antigen-presenting cell was examined by the stimulation of a soluble protein antigen-specific helper T cell hybridoma to secrete interleukin-2. THC exposure significantly reduced the T cell response to the native form of the antigen after a 24-h pretreatment of the macrophages with nanomolar drug concentrations. However, THC did not affect interleukin-2 production when the macrophages presented a synthetic peptide of the antigen to the T cells, suggesting that the drug may interfere with antigen processing, not peptide presentation. Cannabinoid inhibition of the T cell response to the native antigen was stereoselective consistent with the involvement of a cannabinoid (CB) receptor. Bioactive CP-55,940 diminished T cell activation, whereas the inactive stereoisomer CP-56,667 did not. The macrophage hybridoma expressed mRNA for the CB2 but not the CB1 receptor whereas the T cells expressed an extremely low level of mRNA for the CB2 receptor. The CB1-selective antagonist SR141716A did not reverse the suppression caused by THC, demonstrating that the CB1 receptor was not responsible for the drug's inhibitory effect. In contrast, the CB2-selective antagonist SR144528 completely blocked THC's suppression of the T cell response, implicating the participation of the CB2 receptor. These findings suggest that the CB2 receptor may be involved in CB inhibition of antigen processing by macrophages in this system.

Role of a conserved lysine residue in the peripheral cannabinoid receptor (CB2): evidence for subtype specificity.

The human cannabinoid receptors, central cannabinoid receptor (CB1) and peripheral cannabinoid receptor (CB2), share only 44% amino acid identity overall, yet most ligands do not discriminate between receptor subtypes. Site-directed mutagenesis was employed as a means of mapping the ligand recognition site for the human CB2 cannabinoid receptor. A lysine residue in the third transmembrane domain of the CB2 receptor (K109), which is conserved between the CB1 and CB2 receptors, was mutated to alanine or arginine to determine the role of this charged amino acid in receptor function. The analogous mutation in the CB1 receptor (K192A) was found to be crucial for recognition of several cannabinoid compounds excluding (R)-(+)-[2, 3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrrolo[1,2,3-de]-1, 4-benzoxazin-6-yl](1-naphthalenyl)methanone (WIN 55,212-2). In contrast, in human embryonic kidney (HEK)-293 cells expressing the mutant or wild-type CB2 receptors, we found no significant differences in either the binding profile of several cannabinoid ligands nor in inhibition of cAMP accumulation. We identified a high-affinity site for (-)-3-[2-hydroxyl-4-(1, 1-dimethylheptyl)phenyl]-4-[3-hydroxyl propyl] cyclohexan-1-ol (CP-55,940) in the region of helices 3, 6, and 7, with S3.31(112), T3.35(116), and N7.49(295) in the K109A mutant using molecular modeling. The serine residue, unique to the CB2 receptor, was then mutated to glycine in the K109A mutant. This double mutant, K109AS112G, retains the ability to bind aminoalkylindoles but loses affinity for classical cannabinoids, as predicted by the molecular model. Distinct cellular localization of the mutant receptors observed with immunofluorescence also suggests differences in receptor function. In summary, we identified amino acid residues in the CB2 receptor that could lead to subtype specificity.

The central cannabinoid receptor (CB1) mediates inhibition of nitric oxide production by rat microglial cells.

Upon activation, brain microglial cells release proinflammatory mediators, such as nitric oxide (NO), which may play an important role in the central nervous system antibacterial, antiviral, and antitumor activities. However, excessive release of NO has been postulated to elicit immune-mediated neurodegenerative inflammatory processes and to cause brain injury. In the present study, the effect of cannabinoids on the release of NO from endotoxin/cytokine-activated rat cortical microglial cells was evaluated. A drug dose-dependent (0.1 microM-8 microM) inhibition of NO release from rat microglial cells was exerted by the cannabinoid receptor high-affinity binding enantiomer (-)-CP55940. In contrast, a minimal inhibitory effect was exerted by the lower affinity binding paired enantiomer (+)-CP56667. Pretreatment of microglial cells with the Galphai/Galphao protein inactivator pertussis toxin, cyclic AMP reconstitution with the cell-permeable analog dibutyryl-cAMP, or treatment of cells with the Galphas activator cholera toxin, resulted in reversal of the (-)-CP55940-mediated inhibition of NO release. A similar reversal in (-)-CP55940-mediated inhibition of NO release was effected when microglial cells were pretreated with the central cannabinoid receptor (CB1) selective antagonist SR141716A. Mutagenic reverse transcription-polymerase chain reaction, Western immunoblot assay using a CB1 receptor amine terminal domain-specific antibody, and cellular colocalization of CB1 and the microglial marker Griffonia simplicifolia isolectin B4 confirmed the expression of the CB1 receptor in rat microglial cells. Collectively, these results indicate a functional linkage between the CB1 receptor and cannabinoid-mediated inhibition of NO production by rat microglial cells.

High-level expression of the human CB2 cannabinoid receptor using a baculovirus system.

A human CB2 recombinant baculovirus (AcNPV-hCB2) was generated by site-specific transposition and employed to express the human CB2 cannabinoid receptor. Northern analysis of total RNA from Spodoptera frugiperda (Sf9) insect cells infected with AcNPV-hCB2 revealed novel expression of a unique 2.3 kb transcript when probed with hCB2 cDNA. This transcript corresponded to the size expected for hCB2 generated from the recombinant virus construct. Western immunoblot analysis of whole cell homogenates of recombinant baculovirus-infected Sf9 cells, using affinity-purified antibody to a human CB2 carboxy terminal domain (anti-hCB2.CV), revealed the presence of novel immunoreactive protein. In addition, when anti-hCB2.CV was employed in immunofluorescence staining, an intense signal was observed within AcNPV-hCB2-infected cells but not within uninfected cells or cells infected with a control beta-galactosidase recombinant baculovirus. The pattern of immunofluorescence at early periods post-infection was in a perinuclear arrangement with a "signet-ring" appearance, suggestive of glycosylation of the expressed recombinant protein. Transmission electron microscopy revealed regions of intranuclear recombinant virus assembly and the presence of numerous intracytoplasmic proteinaceous vesicular inclusions consistent with hyperproduction of hCB2. Scatchard-Rosenthal analysis of [3H]-(-)3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-[3-hydroxypro pyl]cyclohexan-1-ol ([3H]CP 55,940) receptor binding indicated a Kd of 2.24 nM and a Bmax equal to 5.24 pmol/mg of protein. The lack of [3H]CP 55,940 displacement with N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-met hyl-1H-pyrazole-3-carboxamidehydrochloride (SR 141716A), the CB1-selective antagonist, confirmed the identity of the receptor as CB2. These data indicate that AcNPV-hCB2 expresses high levels of the human CB2, which retains properties of the native receptor. Thus, this recombinant virus may prove suitable for hyperproduction of receptor for basic biochemical and biophysical characterization studies.

Drugs and immunity: cannabinoids and their role in decreased resistance to infectious disease.

Marijuana, Cannabis sativa, elicits a variety of effects in experimental animals and humans. Delta-9-tetrahydrocannabinol (THC) is the major psychoactive component in marijuana. This substance has been shown, also, to be immunosuppressive and to decrease host resistance to bacterial, protozoan, and viral infections. Macrophages, T lymphocytes, and natural killer cells appear to be major targets of the immunosuppressive effects of THC. Definitive data which directly link marijuana use to increased susceptibility to infection in humans currently is unavailable. However, cumulative reports indicating that THC alters resistance to infection in vitro and in a variety of experimental animals support the hypothesis that a similar effect occurs in humans.

Immunohistochemical localization of the neural cannabinoid receptor in rat brain.

The cannabinoid receptor family consists of two inhibitory G-protein-coupled receptors, CB1 and CB2. CB1 is distributed primarily in neural tissue, whereas CB2 is distributed predominantly in immune cells. The distribution of cannabinoid receptors in neural tissue has been demonstrated by using ligand binding autoradiography with CP55,940, a high-affinity cannabinoid receptor ligand, and in situ hybridization. However, the localization of CB1 within individual cells in the brain remains to be defined. In the present study, domain-specific polyclonal antibody to amino acids 83-98 of CB1 was used to define the expression of the neural cannabinoid receptor at the histochemical level. The use of CB1-specific antiserum is advantageous in view of recent reports that CB2 also is expressed in the brain and binds CP55,940. Thus, utilization of anti-CB1 antiserum would allow for the specific detection of CB1 protein expression. The regional staining pattern for CB1 in rat brain was consistent with that reported for CB1 using ligand binding autoradiography and in situ hybridization. Intense immunoreactivity was present in the hippocampal formation, the basal ganglia, and the molecular layer of the cerebellum. Moderate immunohistochemical staining was observed in the olfactory bulb, piriform cortex, cerebral cortex, and the granular layer of the cerebellum. In addition, immunoreactive staining was concentrated on afferent projections and dendritic processes of neuronal cells and was present within cell bodies and on cell surfaces. These data indicate that the anti-CB1 antibody is a sensitive probe for the unequivocal histological discrimination of CB1 protein expression.

In vitro destruction of nerve cell cultures by Acanthamoeba spp.: a transmission and scanning electron microscopy study.

Trophozoites of 4 species of Acanthamoeba were cytopathic for cultured rat B103 neuroblastoma cells. Cytopathogenicity was evaluated by a chromium release assay and by transmission and scanning electron microscopy. Acanthamoeba culbertsoni, Acanthamoeba castellanii, and Acanthamoeba polyphaga destroyed B103 target cells at 37 C as evidenced by the release of radiolabel. Acanthamoeba astronyxis did not produce cytopathology at 37 C but destroyed nerve cells at 25 C. Transmission and scanning electron microscopy of cocultures maintained at different time periods revealed that all species of Acanthamoeba exhibited long cylindrical structures, termed digipodia, which made contact with target cells. Following this effector cell-target cell contact, membrane blebbing on the nerve cells was observed. These events were followed either by lysis of target nerve cells or ingestion of the target cells via food-cups and their subsequent channeling into intracytoplasmic food vacuoles. Use of the TUNEL (TdT-mediated dUTP nick end labeling) technique indicated that approximately 40% of B103 cells incubated with A. culbertsoni, 20% of B103 cells cocultured with A. castellanii or with A. polyphaga, and less than 1% of B103 cells incubated with A. astronyxis at 37 C were apoptotic after 24 hr of coculture. Studies using electron microscopy indicated that Acanthamoeba trophozoites destroyed nerve cells both by cytolysis and by ingestion of whole nerve cells via food-cups.

delta 9-Tetrahydrocannabinol selectively inhibits macrophage costimulatory activity and down-regulates heat-stable antigen expression.

delta 9-Tetrahydrocannabinol (THC) exposure inhibits numerous immunologic functions of macrophages. The ability of THC-exposed macrophages to provide costimulatory signals to helper T cell hybridomas was investigated by induction of interleukin-2 secretion by T cells in response to immobilized monoclonal anti-CD3 antibody. Exogenous interleukin-1 did not deliver a costimulatory signal to these T cells, suggesting that macrophage costimulatory activity was mediated through cell surface molecules. Modulation of the T cell responses by THC depended on the source of costimulation. THC did not suppress costimulatory activity provided by peritoneal macrophages or immobilized fibronectin. THC at low concentrations markedly diminished the costimulatory activity of a macrophage hybridoma to activate one T cell but not another. Inhibition of costimulation by THC inversely correlated with the loss of activity caused by paraformaldehyde fixation of macrophages. THC at 10(-8) M significantly decreased expression of costimulatory heat-stable antigen, which is resistant to fixation, on the macrophage hybridoma. However, expression of costimulatory B7-1 and B7-2 molecules, which are sensitive to fixation, was not affected by THC. Therefore, THC selectively suppresses a fixation-resistant costimulatory signal to helper T cells in part by diminishing expression of heat-stable antigen.

Expression and purification of recombinant human tryptase in a baculovirus system.

B2 is a mAb that recognizes a conformational determinant on the active form of native tryptase, but does not recognize native tryptase that spontaneously loses activity in physiologic buffer. Precursor forms of recombinant human (rh) alpha- and rh beta-tryptase have been expressed in a baculovirus system. In each case, multiple electrophoretic forms were detected in both culture media and cell lysates of infected insect cells by Western blots developed with the G3 mAb made against native human tryptase. Although only 4 of 30 amino acids in the leader sequences of alpha- and beta-tryptase differ, rh alpha-tryptase appeared predominantly in the cell lysates, rh beta-tryptase predominantly in the culture media. B2 recognized rh alpha-tryptase and rh beta-tryptase found in the culture media of infected Sf-9 cells, but not that in cell lysates. Secreted forms of tryptase were purified to homogeneity by B2-immunoaffinity chromatography. From 1 liter of culture fluid 1.5 to 3 mg of rh-tryptase could be purified. Each rh-tryptase precursor was enzymatically inactive with synthetic substrates. Analysis of the N-terminal amino acid sequences of purified rh alpha- and rh beta-tryptase precursors (APAPVQA and APAPGQA, respectively) indicated that the initial 18 amino acids of the 30-amino-acid leader sequence had been removed. Differential N-glycosylation was found in both rh alpha-tryptase (one or two carbohydrate groups per molecule) and rh beta-tryptase (zero or one carbohydrate group per molecule). Thus, the baculovirus expression system is a useful tool for generation of rh alpha- and rh beta-tryptase precursors that exhibit a conformational epitope also present on natural tryptase and that are preferentially secreted into the culture media of infected cells.