B7/CD28 costimulation is critical in susceptibility to Pseudomonas aeruginosa corneal infection: a comparative study using monoclonal antibody blockade and CD28-deficient mice.

Evidence suggests that Pseudomonas aeruginosa stromal keratitis and corneal perforation (susceptibility) is a CD4(+) T cell-regulated inflammatory response following experimental P. aeruginosa infection. This study examined the role of Langerhans cells (LC) and the B7/CD28 costimulatory pathway in P. aeruginosa-infected cornea and the contribution of costimulatory signaling by this pathway to disease pathology. After bacterial challenge, the number of LC infiltrating the central cornea was compared in susceptible C57BL/6 (B6) vs resistant (cornea heals) BALB/c mice. LC were more numerous at 1 and 6 days postinfection (p.i.), but were similar at 4 days p.i., in susceptible vs resistant mice. Mature, B7 positive-stained LC in the cornea and pseudomonas Ag-associated LC in draining cervical lymph nodes also were increased significantly p.i. in susceptible mice. To test the relevance of these data, B6 mice were treated systemically and subconjunctivally with neutralizing B7 (B7-1/B7-2) mAbs. Treatment decreased corneal disease severity and reduced significantly the number of B7-positive cells as well as the recruitment and activation of CD4(+) T cells in the cornea. IFN-gamma mRNA levels also were decreased significantly in the cornea and in draining cervical lymph nodes of mAb-treated mice. When CD28(-/-) animals were tested, they exhibited a less severe disease response (no corneal perforation) than wild-type B6 mice and had a significantly lower delayed-type hypersensitivity response to heat-killed pseudomonas Ag. These results support a critical role for B7/CD28 costimulation in susceptibility to P. aeruginosa ocular infection.

Immortalization of a human prostate stromal cell line using a recombinant retroviral approach.

PURPOSE: We established an immortalized human prostate stromal cell line with retained markers of cell differentiation and alpha1-adrenergic receptor expression. MATERIALS AND METHODS: Primary human prostate stromal explants were infected with an amphotrophic retrovirus encoding the E6/E7 open reading frame of the human papillomavirus type 16. Immunohistochemistry was used to verify the expression of prostate stromal markers. alpha1-Adrenergic receptor expression was investigated using ribonuclease protection assays and radioligand binding. Cell proliferation was measured by the WST-1 assay and cell counting. RESULTS: Clonal isolates of individual prostate stromal cells were isolated and passed in selection media. E6 and E7 expression was verified using reverse transcriptase polymerase chain reaction in the selected cell line. The new prostate stromal cell line PS30 was established which maintains the expression of alpha-smooth muscle actin and expresses 22 fmol./mg. of protein of alpha 1-adrenergic receptors, approximately equal to native human prostate alpha 1-adrenergic receptor expression. However, at a subtype level alpha 1a-adrenergic receptor expression is down-regulated and not detectable by ribonuclease protection assays or radioligand binding, while alpha 1b and alpha 1d-adrenergic receptor expression is enhanced. From a physiological prospective PS30 cells do not form tumors in nude mice and stimulation with phenylephrine does not increase cell proliferation. CONCLUSIONS: We successfully established and characterized an in vitro human prostate stromal cell line. This cell line should facilitate studies designed to characterize the role of the adrenergic nervous system in the regulation of prostate growth.

Prolonged elevation of IL-1 in Pseudomonas aeruginosa ocular infection regulates macrophage-inflammatory protein-2 production, polymorphonuclear neutrophil persistence, and corneal perforation.

The kinetics of IL-1 (alpha and beta) production after Pseudomonas aeruginosa corneal infection was examined in susceptible (cornea perforates) C57BL/6J (B6) and resistant (cornea heals) BALB/cByJ (BALB/c) mice. IL-1alpha and -1beta (mRNA and protein) were elevated in both mouse strains, and levels peaked at 1 day postinfection (p.i. ). Significantly greater amounts of IL-1 protein were detected in B6 vs BALB/c mice at 1 and 3 days p.i. At 5 days p.i., IL-1alpha and -1beta (mRNA and protein) remained elevated in B6, but began to decline in BALB/c mice. To test the significance of elevated IL-1 in B6 mice, a polyclonal neutralizing Ab against IL-1beta was used to treat infected B6 mice. A combination of subconjunctival and i.p. administration of IL-1beta polyclonal Ab significantly reduced corneal disease. The reduction in disease severity in infected B6 mice was accompanied by a reduction in corneal polymorphonuclear neutrophil number, bacterial load, and macrophage inflammatory protein-2 mRNA and protein levels. These data provide evidence that IL-1 is an important contributor to P. aeruginosa corneal infection. At least one mechanism by which prolonged and/or elevated IL-1 expression contributes to irreversible corneal tissue destruction appears to be by increasing macrophage inflammatory protein-2 production, resulting in a prolonged stimulation of polymorphonuclear neutrophil influx into cornea. In contrast, a timely down-regulation of IL-1 appears consistent with an inflammatory response that is sufficient to clear the bacterial infection with less corneal damage.

Alpha2-adrenergic receptors in human dorsal root ganglia: predominance of alpha2b and alpha2c subtype mRNAs.

BACKGROUND: Nonselective alpha2-adrenergic receptor (alpha2AR) agonists (e.g., clonidine) mediate antinociception in part through alpha2ARs in spinal cord dorsal horn; however, use of these agents for analgesia in humans is limited by unwanted sedation and hypotension. The authors previously demonstrated alpha2a approximately alpha2b > > > alpha2c mRNA in human spinal cord dorsal horn cell bodies. However, because 20% of dorsal horn alpha2ARs derive from cell bodies that reside in the associated dorsal root ganglion (DRG), it is important to evaluate alpha2AR expression in this tissue as well. Therefore, the authors evaluated the hypothesis that alpha2b mRNA, alpha2c mRNA, or both are present in human DRG. METHODS: Molecular approaches were used to determine alpha2AR expression in 28 human DRGs because of low overall receptor mRNA expression and small sample size. After creation of synthetic competitor cDNA and establishment of amplification conditions with parallel efficiencies, competitive reverse transcription polymerase chain reaction was performed using RNA isolated from human DRG. RESULTS: Overall expression of alpha2AR mRNA in DRG is low but reproducible at all spinal levels. alpha2b and alpha2cAR subtype mRNAs predominate (alpha2b approximately alpha2c), accounting for more than 95% of the total alpha2AR mRNA in DRG at all human spinal nerve root levels. CONCLUSIONS: Predominance of alpha2b and alpha2cAR mRNA in human DRG is distinct from alpha2AR mRNA expression in cell bodies originating in human spinal cord dorsal horn, where alpha2a and alpha2b predominate with little or absent alpha2c expression. These findings also highlight species heterogeneity in alpha2AR expression in DRG. If confirmed at a protein level, these findings provide an additional step in unraveling mechanisms involved in complex neural pathways such as those for pain.

Subtype specific regulation of human vascular alpha(1)-adrenergic receptors by vessel bed and age.

BACKGROUND: alpha(1)-adrenergic receptors (alpha(1)ARs) regulate blood pressure, regional vascular resistance, and venous capacitance; the exact subtype (alpha(1a), alpha(1b), alpha(1 d)) mediating these effects is unknown and varies with species studied. In order to understand mechanisms underlying cardiovascular responses to acute stress and chronic catecholamine exposure (as seen with aging), we tested two hypotheses: (1) human alpha(1)AR subtype expression differs with vascular bed, and (2) age influences human vascular alpha(1)AR subtype expression. METHODS AND RESULTS: Five hundred vessels from 384 patients were examined for alpha(1)AR subtype distribution at mRNA and protein levels (RNase protection assays, ligand binding, contraction assays). Overall vessel alpha(1)AR density is 16+/-2.3fmol/mg total protein. alpha(1a)AR predominates in arteries at mRNA (P<0.001) and protein (P<0.05) levels; all 3 subtypes are present in veins. Furthermore, alpha(1)AR mRNA subtype expression varies with vessel bed (alpha(1a) higher in splanchnic versus central arteries, P<0.05); competition analysis (selected vessels) and functional assays demonstrate alpha(1a) and alpha(1b)-mediated mammary artery contraction. Overall alpha(1)AR expression doubles with age (<55 versus > or = 65 years) in mammary artery (no change in saphenous vein), accompanied by increased alpha(1b)>alpha(1a) expression (P< = 0.001). CONCLUSIONS: Human vascular alpha(1)AR subtype distribution differs from animal models, varies with vessel bed, correlates with contraction in mammary artery, and is modulated by aging. These findings provide potential novel targets for therapeutic intervention in many clinical settings.

Alpha1-adrenergic receptor subtypes in human detrusor.

PURPOSE: To identify and quantitate alpha1-adrenergic receptor (alpha1AR) subtype expression in human detrusor. MATERIALS AND METHODS: Initial studies to determine alpha1AR expression in human detrusor were performed using saturation binding with [125I]HEAT. Once the presence of alpha1ARs was documented, subtype (alpha1a, alpha1b, alpha1d) expression at the mRNA level (and comparison with rat) was determined with RNase protection assays (human detrusor) and RT-PCR (human detrusor, rat whole bladder). Competition binding analysis with the alpha1dAR-selective ligand BMY7378 was used to measure alpha1AR subtype expression at a protein level in human detrusor. RESULTS: Alpha1AR expression in human detrusor was low but reproducible (6.3 +/- 1.0 fmol./mg. total protein). RNase protection assays performed on total RNA extracted from human detrusor revealed the following alpha1AR subtype expression: alpha1d (66%) > alpha1a (34%), and no alpha1b. RT-PCR confirmed alpha1AR subtype mRNA distribution in human detrusor with alpha1d (approximately 60-70%) > alpha1a (approximately 30-40%), and a lack of alpha1b mRNA. Rat whole bladder expressed different alpha1AR subtype mRNA than human detrusor, with alpha1a approximately alpha1b approximately alpha1d. The presence of alpha1d > alpha1a expression in human detrusor was confirmed at a protein level by competition analysis utilizing BMY7378 which revealed a two-site fit, with Ki and high affinity binding (66%) consistent with the alpha1dAR subtype. CONCLUSIONS: Human detrusor contained two alpha1AR subtypes (alpha1d > alpha1a), a finding that is different from rat, another commonly used animal model. Since non-subtype selective alpha1AR antagonists ameliorate irritative bladder symptoms (in men and women with/without outlet obstruction), and Rec 15/2739 (alpha1a selective antagonist) does not improve symptom scores in BPH, our findings suggest bladder alpha1dARs may provide a potentially novel mechanism underlying these therapeutic benefits.

Transcriptional regulation of the human alpha1a-adrenergic receptor gene. Characterization Of the 5'-regulatory and promoter region.

We recently cloned cDNAs encoding three subtypes of human alpha1-adrenergic receptors (alpha1ARs), alpha1a, alpha1b, and alpha1d (Schwinn, D. A., Johnston, G. L., Page, S. O., Mosley, M. J., Wilson, K. H., Worman, N. P., Campbell, S., Fidock, M. D., Furness, L. M., Parry-Smith, D. J., Peter, B., and Bailey, D. S. (1995) J. Pharmacol. Exp. Ther. 272, 134-142) and demonstrated predominance of alpha1aARs in many human tissues (Price, D. T., Lefkowitz, R. J., Caron, M. G., Berkowitz, D., and Schwinn, D. A. (1994) Mol. Pharmacol. 45, 171-175). Several lines of evidence indicate that alpha1aARs are important in clinical diseases such as myocardial hypertrophy and benign prostatic hyperplasia. Therefore, we initiated studies to understand mechanisms underlying regulation of alpha1aAR gene transcription. A genomic clone containing 6.2 kb of 5'-untranslated region of the human alpha1aAR gene was recently isolated. Ribonuclease protection and primer extension assays indicate that alpha1aAR gene transcription occurs at multiple initiation sites with the major site located 696 base pairs upstream of the ATG, where a classic initiator sequence is located. Transfection of luciferase reporter constructs containing varying amounts of 5'-untranslated region into human SK-N-MC neuroblastoma cells indicate that a region extending 125 base pairs upstream from the main transcription initiation site contains full alpha1aAR promoter activity. Furthermore, distinct activator and suppressor elements lie 2-3 and 3-5 kilobase pairs upstream, respectively. Although the alpha1aAR promoter contains neither TATA or CAAT elements, gel shift mobility assays targeting three GC boxes immediately upstream of the main transcription initiation site confirm binding of Sp1. Activity of the alpha1aAR promoter is cell-specific, demonstrating highest activity in cells endogenously expressing alpha1aARs. The human alpha1aAR gene also contains several cis regulatory elements, including several insulin and cAMP response elements. Consistent with these observations, we provide the first evidence that treatment of SK-N-MC cells with insulin and cAMP elevating agents leads to an increase in alpha1aAR expression. In conclusion, these data represent the first characterization of the alpha1aAR gene; our findings should facilitate further studies designed to understand mechanisms regulating alpha1AR subtype-specific expression in healthy and diseased human tissue.

Biogenesis, cellular localization, and functional activation of the heat-stable enterotoxin receptor (guanylyl cyclase C).

Enterotoxigenic Escherichia coli elaborate a peptide called heat-stable enterotoxin (ST), which binds to and activates the intestinal ST receptor (STaR). STaR, also known as guanylyl cyclase C (GC-C), is a member of the transmembrane guanylyl cyclase receptor family. The mRNA for STaR encodes an approximately 120 kDa protein with the N-terminal ligand binding domain on the cell surface. Ligand affinity cross-linking studies have previously demonstrated several species of potential ST binding proteins, ranging in size from approximately 50 to 160 kDa. Although these smaller forms of STaR (50-80 kDa) have been proposed to act in vivo as toxin binding proteins, their biogenesis and localization have not previously been examined. Using pulse labeling in vivo and synchronized translation in vitro, we demonstrate that these smaller forms represent incomplete translational products and are not formed through limited proteolysis of the full-length receptor, as had previously been believed. We determined, using fluorescence confocal microscopy and surface labeling, that only approximately 25% of cellular receptors are expressed at the surface, while the remaining population is retained within the endoplasmic reticulum. Only full-length receptor is found at the surface of the cell, indicating this to be the biologically active form of STaR responsible for interacting with the heat-stable enterotoxin and other luminal intestinal peptides. The large intracellular receptor population, and potential for function before translocation to the cell surface, may impact on how pharmacologic modulators of this clinically important receptor are designed.

Molecular cloning and characterization of SCaMPER, a sphingolipid Ca2+ release-mediating protein from endoplasmic reticulum.

Release of Ca2+ stored in endoplasmic reticulum is a ubiquitous mechanism involved in cellular signal transduction, proliferation, and apoptosis. Recently, sphingolipid metabolites have been recognized as mediators of intracellular Ca2+ release, through their action at a previously undescribed intracellular Ca2+ channel. Here we describe the molecular cloning and characterization of a protein that causes the expression of sphingosyl-phosphocholine-mediated Ca2+ release when its complementary RNA is injected into Xenopus oocytes. SCaMPER (for sphingolipid Ca2+ release-mediating protein of endoplasmic reticulum) is an 181 amino acid protein with two putative membrane-spanning domains. SCaMPER is incorporated into microsomes upon expression in SO cells or after translation in vitro. It mediates Ca2+ release at 4 degrees C as well as 22 degrees C, consistent with having ion channel function. The EC50 for Ca2+ release from Xenopus oocytes is 40 microM, similar to sphingosyl-phosphocholine-mediated Ca2+ release from permeabilized mammalian cells. Because Ca2+ release is not blocked by ryanodine or La3+, the activity described here is distinct from the Ca2+ release activity of the ryanodine receptor and the inositol 1,4,5-trisphosphate receptor. The properties of SCaMPER are identical to those of the sphingolipid-gated Ca2+ channel that we have previously described. These findings suggest that SCaMPER is a sphingolipid-gated Ca2+-permeable channel and support its role as a mediator of this pathway for intracellular Ca2+ signal transduction.

Regulation of cell signaling by the cytoplasmic domains of the heat-stable enterotoxin receptor: identification of autoinhibitory and activating motifs.

Infection with enterotoxigenic Escherichia coli is a leading cause of traveler's diarrhea. Many enterotoxigenic E. coli strains produce heat-stable enterotoxin (ST), a peptide that binds to the intestinal receptor guanylyl cyclase C known as STaR. The toxin-receptor interaction elevates intracellular cGMP, which then activates apical chloride secretion, resulting in secretory diarrhea. In this report, we examine how the intracellular domains of STaR participate in the propagation and regulation of signaling. We show that STaR exists as an oligomer in both the presence and the absence of toxin. We also demonstrate that deletion of the intracellular kinase-homology domain produces a constitutively active mutant, suggesting that this domain subserves an autoinhibitory function. Finally, we constructed a point mutant within a highly conserved region of the cyclase domain that completely inactivates the catalytic activity of guanylyl cyclase. Cotransfection of this point mutant with wild-type receptor causes a dominant-negative effect on receptor activation. This suggests that interaction of receptor subunits is required for toxin-induced activation and that the cyclase domain is involved in this essential interaction. We propose that the binding of ST to STaR promotes a conformational change across the cell membrane. This removes the inhibitory effects of the kinase-homology domain and promotes an interaction between cyclase domains that leads to receptor activation. The data suggest a paradigm of signal transduction that may also be relevant to other members of the guanylyl cyclase receptor family.

In the immature mouse, Pseudomonas aeruginosa pili bind a 57-kd (alpha 2-6) sialylated corneal epithelial cell surface protein: a first step in infection.

PURPOSE: To test the hypothesis that in the unscarified immature eye, Pseudomonas aeruginosa pili bind glycoprotein receptors, one or more of which are surface associated. METHODS: Several methods--including radioiodination of bacterial pili and surface-associated corneal epithelial proteins (CEPs), solid-phase binding assays, carbohydrate detection, and immunoblotting techniques in which periodate oxidation and preincubation of blots with purified pili, neuraminidase, sialic acid, other sugars, and SNA and MAA lectins--were used to identify and characterize host proteins. Some of these proteins in the immature mouse corneal epithelium interacted with bacterial pili. RESULTS: Seven proteins, with molecular weights from 14 to 66 kd were identified that strongly bound PAK/PR1 pili. To determine if any protein(s) was cell surface localized, corneal epithelial surface membrane proteins were radioiodinated and examined using a pilus overlay assay and lectin analysis. Only one protein of 57 kd was cell surface labeled and bound pili in an overlay assay. This protein was alpha (2-6) sialylated, as shown by SNA binding. Furthermore, SNA lectin was able to block pilus binding to CEPs. 125I labeling of pili and a solid-phase binding assay confirmed that pili bind to CEPs and, further, that binding could be competitively inhibited by excess unlabeled pili and that the receptors appeared saturable. GlycoTrack reagents were used to show that the epithelial proteins of the postnatal day 5 (P5) mouse cornea were glycosylated. Removal of carbohydrates by preincubation of blots with periodate, or combining pili with sialic acid, eliminated pili binding. Pretreatment of blots with either neuraminidase (N'ase) to decrease and/or remove sialic acid residues, or pretreatment with SNA lectin with specificity for alpha (2-6) linked sialic acid to galactose, also diminished pili binding to CEPs. Other sugars or MAA lectin, specific for sialic acid alpha (2-3) linked to galactose, had no inhibitory effect. CONCLUSIONS: These data show that a 57-kd surface membrane protein bound pili in the immature cornea and that for both this protein and the other nonsurface proteins, sialic acid alpha (2-6) linked to galactose was important in receptor recognition by the pilus adhesion. The 57-kd protein is putatively important in the initial interaction of pili with the unwounded ocular epithelium and may be the initial pathogenic event in this model.

Investigations on the role of flagella in adhesion of Pseudomonas aeruginosa to mouse and human corneal epithelial proteins.

Antiflagellar monoclonal antibodies (MAbs) were used in an overlay assay to determine whether flagella bind to blots of mouse and human corneal epithelial proteins (CEPs). The role of carbohydrates and surface charge was also explored by preincubation of blots with periodate or neuraminidase, or flagella with monosaccharides or charged compounds, respectively. Periodate slightly decreased binding of flagella, while sialic acid inhibited binding, and the effect was dose dependent. Neuraminidase treatment of blots or incubation of flagella with a negatively, but not a positively charged compound, also blocked binding. The data suggest that flagella interact with mouse and human CEPs by electrostatic mechanisms.

Immunization with homologous Pseudomonas aeruginosa pili protects against ocular disease.

The prophylactic effect of pili in prevention or amelioration of Pseudomonas aeruginosa ocular disease was examined in mice, using both systemic and topical protection approaches. At 30 days postinfection, a significant number of animals actively or passively immunized with pili homologous to pseudomonal strain American Type Culture Collection 19660 were protected from ocular disease when compared with similarly infected phosphate-buffered saline controls. Although exogenously mixing strain 19660 with either homologous or heterologous (PAK/PR1) pili before topical application of the inoculum significantly inhibited bacterial adhesion in vitro, in similarly designed in vivo studies, animals were not protected from corneal disease. Neither was significant ocular protection conferred using pili (PAK/PR1) heterologous to the infecting strain (19660) for active or passive immunization of mice, nor in studies involving exogenous mixing of PAK/PR1 pili or its pili-specific monoclonal antibody with strain 19660 prior to topical application of the latter. These results provide evidence that significant ocular protection is achieved by either active or passive, but not topical, immunization with pili homologous to the infecting bacterial strain and that immunization with pili heterologous to the infecting bacterial strain fails to provide protection against ocular disease, despite the fact that heterologous pili are highly effective at decreasing bacterial binding to cornea in vitro.

Systemic and topical protection studies using Pseudomonas aeruginosa flagella in an ocular model of infection.

Purified flagella from P. aeruginosa ATCC 19660 were used for active, passive, or topical immunization prior to corneal challenge with strain 19660. At 30 days post-infection, a significant number of mice actively or passively immunized with flagella and infected with the homologous bacterial strain were protected from ocular disease when compared to control animals. In topical immunization studies, premixing of 19660 flagella with the bacterial inoculum prior to ocular challenge with strain 19660, provided results similar to those of the active or passive immunization studies. A reduced lipopolysaccharide (LPS:1 E.U./mg) flagella preparation was also produced and used similarly. Again, significant protection was achieved in mice immunized by flagella regardless of the immunization route. An in vitro adherence assay also was performed to examine quantitatively the effect of exogenously applied flagella, or an antiflagella monoclonal antibody (MAb) on bacterial adhesion. Premixing of the bacterial inoculum with flagella or the MAb prior to applying it topically to corneas in organ culture all significantly inhibited bacterial binding. These results strongly suggest that significant ocular protection is achieved with either active or passive immunization, or premixing of the bacterial inoculum with flagella from strain 19660 prior to ocular challenge with the homologous bacterial strain. They also indicate that topical application of flagella or antiflagella MAb provide protection against ocular disease by decreasing bacterial adhesion to cornea.

Corneal epithelial glycoproteins exhibit Pseudomonas aeruginosa pilus binding activity.

Adherence of Pseudomonas aeruginosa to the cornea is a requisite step in the pathogenesis of bacteria-induced corneal disease. P. aeruginosa is capable of attaching to host epithelial cells by its pili, but there is little information regarding the epithelial receptors of this adhesin in the cornea. Using nitro-cellulose blotting of polyacrylamide gels of solubilized adult mouse corneal epithelium, four major proteins (molecular weights: 38, 42, 57, and 66 kD) and several minor proteins were identified that bound purified pili from strain PAK and its hyperpiliated mutant PAK/PR1. These proteins were identified by immunoblotting either with pilus-specific monoclonal antibodies, XLR-3 and PK 3B, or using peptide PAK 128-144 (OX). The glycosylated nature of the proteins was determined using similar gel electrophoresis of corneal epithelial proteins, blotting onto nitrocellulose, and staining the blots with lectins conjugated to either horseradish peroxidase or alkaline phosphatase. All four major pilus-binding proteins were stained with concanavalin A lectin (mannose and glucose) and either wheat germ agglutinin lectin (WGA, specific for sialic acid and N-acetylglucosamine) or succinylated WGA lectin (only N-acetylglucosamine). Staining for peanut agglutinin lectin (galactose beta(1-3) N-acetylgalactosamine) was seen for the 42-, 57-, and 66-kD proteins. The importance of the carbohydrate portions of these corneal proteins in pili binding was confirmed by preincubation of corneal epithelial blots with periodate or pili with sialic acid, both of which abolished the pili binding. These studies indicate that corneal epithelial pilus-binding proteins are glycoproteins in nature and that sialic acid may be a constituent of these pilus-specific receptors in the adult mouse corneal epithelium.

Analysis of adhesion, piliation, protease production and ocular infectivity of several P. aeruginosa strains.

The role of bacterial piliation and protease production in Pseudomonas aeruginosa adhesion to the injured corneal epithelial surface and subsequent infectivity was examined using several bacterial strains, including three that were hyperpiliated. To initiate this study, bacteria were examined by transmission EM to confirm their piliation characteristics. The PAK strain, like pseudomonas ATCC 19660, possessed about 1-4 polar pili. The mutant PAK/PR11 lacked pili while PAK/PR1, DB2, a mutant of PAO1, and PA1244, a wild-type clinical isolate, were hyperpiliated. Ocular infectivity of these bacterial strains and mutants was examined macroscopically and histopathologically in mice and these data compared to the well-characterized ocular disease response of a murine model of infection with pseudomonas ATCC 19660. The PAK strain was infective, but less virulent than strain 19660 by both macroscopic grading and histopathological analysis of infected eyes. Infectivity of the PR11 mutant was similar to the PAK parent strain, while PR1, DB2 and 1244, all hyperpiliated, were not infective. To explore the hypothesis that hyperpiliated bacteria bound less well to cornea and thus failed to induce corneal disease, in vitro quantitative studies of bacterial adhesion were done using an ocular organ culture model. The PR1 hyperpiliated mutant bound significantly less well to cornea than the PAK parent strain, PR11 mutant or pseudomonas 19660, while DB2 and 1244 binding did not differ significantly from 19660 or PAK. Examination of protease production, another factor which may influence adhesion, revealed that only 19660 and DB2 produced detectable protease. This study provides evidence that non-piliated, non-protease producing strains such as PAK/PR11 possess alternate virulence mechanisms to facilitate binding to and infectivity of corneal tissue.