Proinflammatory stimuli regulate endothelial hyaluronan expression and CD44/HA-dependent primary adhesion.

The localization of circulating leukocytes within inflamed tissues occurs as the result of interactions with and migration across vascular endothelium, and is governed, in part, by the expression of adhesion molecules on both cell types. Recently, we have described a novel primary adhesion interaction between the structurally activated form of the adhesion molecule CD44 on lymphocytes and its major ligand hyaluronan on endothelial cells under physiologic laminar flow conditions, and have proposed that this interaction functions in an extravasation pathway for lymphocytes in vascular beds at sites of inflammation. While the regulation of activated CD44 on leukocytes has been characterized in depth, regulation of hyaluronate (HA) on endothelial cells has not been extensively studied. Here we demonstrate that the expression of HA on cultured endothelial cell lines and primary endothelial cultures is inducible by the proinflammatory cytokines TNFalpha and IL-1beta, as well as bacterial lipopolysaccharide. In addition, this inducibility appears strikingly restricted to endothelial cells derived from microvascular, but not large vessel, sources. The elevated HA levels thus induced result in increased CD44-dependent adhesive interactions in both nonstatic shear and laminar flow adhesion assays. Changes in mRNA levels for the described HA synthetic and degradative enzymes were not found, suggesting other more complex mechanisms of regulation. Together, these data add to the selectin and immunoglobulin gene families a new inducible endothelial adhesive molecule, hyaluronan, and help to further our understanding of the potential physiologic roles of the CD44/HA interaction; i.e., local cytokine production within inflamed vascular beds may enhance surface hyaluronan expression on endothelial cells, thereby creating local sites receptive to the CD44/HA interaction and thus extravasation of inflammatory cells.

The route of antigen entry determines the requirement for L-selectin during immune responses.

L-selectin, an adhesion molecule constitutively expressed on leukocytes, is important for primary adhesion and extravasation of lymphocytes at specialized high endothelial venules within lymph nodes and other leukocytes at sites of inflammation. We have generated L-selectin-deficient mice by targeted disruption, and have confirmed a previously reported phenotype which includes strikingly impaired contact hypersensitivity (CHS) responses to reactive haptens (Tedder, T.F., D.A. Steeber, and P. Pizcueta. 1995. J. Exp. Med. 181:2259-2264; Xu, J.C., I.S. Grewal, G.P. Geba, and R.A. Flavell. 1996. 183:589-598.). Since the mechanism of this impairment has not been clarified, we sought to define the stage(s) at which the CHS response is affected in L-selectin-deficient mice. We show that epidermal Langerhans cells in L-selectin-deficient mice are normal in number, migrate to peripheral lymph nodes appropriately, and are functional in presenting allogeneic and haptenic antigens. Moreover, T cells, as well as neutrophil and monocyte effector populations, are fully capable of entry into the inflamed skin sites in the absence of L-selectin. Thus, antigen presentation and effector mechanisms are intact in L-selectin deficient mice. In contrast, virtually no antigen-specific T cells can be found within draining peripheral nodes after a contact challenge, suggesting that the defect resides primarily in the inability of antigen-specific T cells to home to and be activated in these nodes. Indeed, L-selectin-deficient mice mount completely normal CHS responses when alternate routes of immunization are used. These studies pinpoint the lesion in CHS to a discrete stage of the afferent limb of the response, clarify the role of L-selectin on effector populations, and illustrate the critical importance of the route of antigen entry to the successful execution of an immune response.

Molecular mimicry, anti-coxsackievirus B3 neutralizing monoclonal antibodies, and myocarditis.

Molecular mimicry has been suggested as one mechanism to explain chronic myocarditis in some murine strains in the postinfectious period following induction of acute myocarditis by coxsackievirus B3 (CVB3). To test this hypothesis, neutralizing mAbs were generated against a highly myocarditic CVB3 virus (CVB3m). These mAbs neutralized several myocarditic and amyocarditic CVB3 variants by cytopathic effects inhibition assays. Data from several experiments suggest that these mAbs recognize discontinuous epitopes on CVB3m capsid proteins. Several mAbs were found to induce cardiopathologic alterations subsequent to i.p. inoculation of normal adolescent male CD-1 or C3H/HeJ mice. Immunocytochemical assays demonstrated significant binding of two mAbs to the surface of normal cultured murine cardiac fibroblasts. Also, several mAbs were shown to participate in C-mediated lysis of normal cardiac fibroblasts, but this property did not correlate well with cardiopathogenic potential. The two properties of a mAb that were the best predictors for cardiopathogenic potential were the capacity for stimulation of normal murine fibroblasts to produce a chemoattractant activity for unelicted murine peritoneal macrophages, and the capacity for recognition of an epitopes(s) on murine or human cardiac myosins. These data show that some anti-CVB3m neutralizing mAbs can participate in proinflammatory reactions in vitro and induce cardiopathologic alterations in vivo, suggesting one mechanism by which CVB3-induced chronic inflammation in murine heart tissues can be sustained in the absence of continued virus replication.

Anti-Coxsackievirus B3 neutralizing antibodies with pathological potential.

Adolescent CD-1 mice inoculated with coxsackievirus B3 (CVB3m) will develop acute myocarditis with focal lesions by 7 days post-inoculation (p.i.). Administration of murine sera containing anti-CVB3m-neutralizing antibodies into CVB3m-inoculated mice at 3 days p.i. will exacerbate myocarditis, suggesting the presence of pathological antibodies. To study potential pro-inflammatory properties of virus-induced antibodies, a panel of anti-CVB3m-neutralizing monoclonal antibodies (mAbs) was generated. Several studies demonstrated shared epitopes between CVB3m particles and cultured murine cardiac or neonatal skin fibroblasts: (1) one or more mAbs bound to cultured cardiac fibroblasts; (2) several mAbs can participate in complement-mediated lysis of neonatal skin fibroblasts; and (3) at least one mAbs stimulated synthesis of a macrophage chemoattractant from cultured neonatal skin fibroblasts. Injection of one mAb in three doses, each of about 5 micrograms, into adolescent male CD-1 mice induced focal myocarditic lesions which were similar to CVB3m-induced lesions. One mAb induced a diffuse interstitial hypercellularity in most mice and two mAbs did not induce detectable cardiopathology. These data suggest that some anti-CVB3m neutralizing idiotypes (antibodies) which initially can provide protection via virus clearance mechanisms can also bind to cross-reacting epitopes on normal tissues. Binding of antibodies to normal heart tissues could stimulate proinflammatory reactions by several mechanisms and sustain myocarditis.

Characterization of the antibody response in vaccinated mice protected against Coxsackievirus B3-induced myocarditis.

Adolescent male CD-1 mice can be rendered resistant to coxsackievirus B3 (CVB3m)-induced myocarditis following inoculation as neonates with a single dose of a temperature-sensitive mutant virus (ts1), derived from the prototype parent virus (CVB3m). Previously, anti-CVB3 neutralizing antibodies were not detected in sera of adolescent ts1 vaccinees by a standard plaque-reduction assay (Gauntt et al 1983. Infect. Immun. 39:851). However, a more sensitive cytopathic effects-reduction assay permitted detection of low titers of anti-CVB3m neutralizing antibodies of the IgG class prior to challenge with CVB3m. Following CVB3m challenge, serum anti-CVB3m neutralizing antibody titers of ts1 vaccines declined on days 1-2 post-inoculation (p.i.) then increased over the next 6 days. The neutralizing antibodies were of both the IgG and IgM classes. Normal mice challenged with CVB3 did not produce detectable serum anti-CVB3m neutralizing antibody until day 4 p.i. and by 8 days p.i. the neutralizing antibody was only of the IgM class. Thus, adolescent murine ts1 vaccines mount a secondary antibody response to CVB3m in both neutralizing IgG and IgM, but resistance to CVB3m-induced myocarditis is due to the presence of low levels of anti-CVB3m IgG neutralizing antibody in serum at the time of challenge with CVB3m.

Antimyocarditic activity of the guanine derivative BIOLF-70 in a coxsackievirus B3 murine model.

Prophylactic administration of a nontoxic dose of 9-[[2-benzyloxyl-1-(benzyloxymethyl)ethoxy]methyl]-6-chlo roguanine (BIOLF-70) to mice reduced the number of myocarditic lesions induced by coxsackievirus B3 (CVB3). BIOLF-70 exhibited minimal antiviral activity against CVB3 in HeLa cells and murine neonatal skin fibroblasts and minimally reduced CVB3 yields in heart tissues. The drug had no effect on serum anti-CVB3 neutralizing antibody titers and did not induce the production of interferon. Flow microfluorometric analyses of splenic lymphocytes taken from BIOLF-70-treated, CVB3-inoculated mice at 7 days postinoculation showed that the proportion of T lymphocytes was increased, as measured by fluorescent staining of Thy-1 and Lyt-2 surface markers, compared with the proportion of T lymphocytes in splenic cells from virus-inoculated or BIOLF-70-treated or normal groups of mice. Splenic lymphocytes from BIOLF-70-treated, CVB3-inoculated mice showed reduced cytotoxic activity against CVB3-infected target fibroblasts. Splenic cells from BIOLF-70-treated, CVB3-inoculated mice had slightly higher natural killer cell activity than did those from the other three groups of mice, which had comparatively similar levels of natural killer cell activity. The data suggest that BIOLF-70 exerts antimyocarditic activity perhaps by some antiviral activity in heart tissues and by immunomodulatory mechanisms which appear to involve T suppressor or T cytotoxic lymphocyte subpopulations and natural killer cells.

Murine forebrain anomalies induced by coxsackievirus B3 variants.

Neonatal or 7-day-old mice inoculated intracranially with either of two temperature-sensitive mutants (ts1, ts6) or the parent coxsackievirus B3 (CVB3) subsequently developed porencephaly or hydranencephaly. The forebrain anomaly induced depended upon age of the animal at inoculation and virus variant inoculated. Sections of brains from hydranencephalic mice revealed severe meningeal reactions, necrotizing encephalitis, and liquifactive necrosis in the cerebrum. No pathology was found in the pons, medulla, or cerebellum. Immunofluorescence studies with hyperimmune anti-CVB3 antiserum showed a random distribution of virus-infected cells in the cerebrum. Virus was recovered from several organs but little to no interferon and no anti-CVB3 neutralizing antibody were present in brain tissues. Availability of cells for replication of virus at the time of inoculation and replicative properties of each virus likely contributed to the outcome. Thus, forebrain anomalies resembling those found in infants can be induced in a murine model by select variants of coxsackievirus B3.

The inability of in vitro transforming SV40 subgenomes to cause tumors in vivo.

Linear or subgenomic SV40 DNAs were transfected into cells from a variety of species (including rodent, dog, muntjak, and monkey) and injected subcutaneously into neonate Syrian hamsters for tumorigenicity testing. The 'early-region' subgenomes were capable of transforming cells in vitro. Complete genomes or complementary subgenomes could transform nonpermissive and semipermissive cells, were infectious for permissive cells, and induced tumors from which infectious virus could be rescued. Tumors were not formed in neonate hamsters upon injection with subgenomic SV40 DNAs, even those capable of transforming cells in vitro. These results suggested that SV40 tumor formation in vivo may require a complete genome.