Binding of the 68-kilodalton protein of Mycobacterium avium to alpha(v)beta3 on human monocyte-derived macrophages enhances complement receptor type 3 expression

Isolation of high-affinity single-chain antibodies against Mycobacterium avium subsp. paratuberculosis surface proteins from sheep with Johne's disease

Johne's disease, caused by infection with Mycobacterium avium subsp. paratuberculosis, causes significant economic losses to the livestock farming industry. Improved investigative and diagnostic tools-necessary to understand disease processes and to identify subclinical infection-are much sought after. Here, we describe the production of single-chain antibodies with defined specificity for M. avium subsp. paratuberculosis surface proteins. Single-chain antibodies (scFv) were generated from sheep with Johne's disease by cloning heavy-chain and lambda light-chain variable regions and expressing these in fusion with gene III of filamentous phages. Two scFv clones (designated SurfS1.2 and SurfS2.2) were shown to be immunoreactive against M. avium subsp. paratuberculosis surface targets by flow cytometry, and immunoblotting identified specificity for a 34-kDa proteinase-susceptible determinant. Both antibodies were cross-reactive against Mycobacterium avium subsp. avium but nonreactive against Mycobacterium bovis or Mycobacterium phlei cells and were shown to be capable of enriching M. avium subsp. paratuberculosis cells by a factor of approximately 10(6)-fold when employed in magnetic bead separation of mixed Mycobacterium sp. cultures. Further, magnetic bead separation using SurfS1.2 and SurfS2.2 was capable of isolating as few as 10(3) M. avium subsp. paratuberculosis cells from ovine fecal samples, indicating the diagnostic potential of these reagents. Finally, inclusion of SurfS1.2 or SurfS2.2 in in vitro broth culture with M. avium subsp. paratuberculosis indicated that surface binding activity did not impede bacterial growth, although colony clumping was prevented. These results are discussed in terms of the potential use of single-chain phage display monoclonal antibodies as novel diagnostic reagents.

A comparison of ovine monocyte-derived macrophage function following infection with Mycobacterium avium ssp. avium and Mycobacterium avium ssp. paratuberculosis

Mycobacterium avium ssp. paratuberculosis causes Johne's disease in ruminants, whereas the antigenically and genetically similar subspecies Mycobacterium avium ssp. avium is less virulent. In this study, we compared one strain of each subspecies for its ability to survive, induce cytokines, suppress MHC class I and II expression and induce apoptosis or necrosis in ovine monocyte-derived macrophages. Both subspecies survived intracellularly and induced the secretion of IL-10. Low levels of TNF-alpha were detected after infection with both subspecies at 4 h. IL-12 was not upregulated after infection. Downregulation of MHC class I and II was evident in response to infection with both M. avium ssp. avium and M. avium ssp. paratuberculosis. No significant cytotoxicity was detectable in ovine macrophages after the addition of bacteria. M. avium ssp. paratuberculosis induced slightly more apoptosis than M. avium ssp. avium. Still the overall rate of apoptosis was very low and both subspecies suppressed LPS-induced macrophage apoptosis.

Identification of heat shock protein 60 as the ligand on Histoplasma capsulatum that mediates binding to CD18 receptors on human macrophages

Histoplasma capsulatum (Hc), is a facultative intracellular fungus that binds to CD11/CD18 receptors on macrophages (Mphi). To identify the ligand(s) on Hc yeasts that is recognized by Mphi, purified human complement receptor type 3 (CR3, CD11b/CD18) was used to probe a Far Western blot of a detergent extract of Hc cell wall and cell membrane. CR3 recognized a single 60-kDa protein, which was identified as heat shock protein 60 (hsp60). Biotinylation of viable yeasts, followed by precipitation with streptavidin-coated beads, and Western blotting with anti-hsp60 demonstrated that hsp60 was on the surface of Hc yeasts. Electron and confocal microscopy revealed that hsp60 resided on the yeast cell wall in discrete clusters. Recombinant hsp60 (rhsp60) inhibited attachment of Hc yeasts to Mphi. Recombinant hsp60 and Abs to CD11b and CD18 inhibited binding of yeasts to Chinese hamster ovary cells transfected with CR3 (CHO3). Polystyrene beads coated with rhsp60 bound to Mphi, and attachment was inhibited by Abs to CD11 and CD18. Freeze/thaw extract (F/TE), a preparation of Hc yeast surface proteins that contained hsp60, inhibited the attachment of Hc yeasts to Mphi. Depletion of hsp60 from F/TE removed the capacity of F/TE to block binding of Hc to Mphi. Interestingly, rhsp60 did not inhibit binding of Hc yeasts to dendritic cells (DC), which recognize Hc via very late Ag 5. Moreover, F/TE inhibited attachment of Hc to DC even when depleted of hsp60. Thus, Hc hsp60 appears to be a major ligand that mediates attachment of Hc to Mphi CD11/CD18, whereas DC recognize Hc via a different ligand(s).

Pathogenesis of nontuberculous mycobacteria infections

M avium is a microorganism well adapted to living in the environment and in different hosts. During the past 15 years, a substantial amount of information has been accumulated about the mechanisms used by M avium to cross the host's mucosal barrier, replicate inside cells, circumvent the host's immune response, and persist inside the host. It turns out that M avium is a fascinating pathogen after all. The increasing knowledge about M avium pathogenesis may one day provide means for a more effective prophylaxis as well as for treatment of the infection.

Involvement of integrin alphavbeta3 in the pathogenesis of human immunodeficiency virus type 1 infection in monocytes

Attachment of HIV to macrophages is a critical early event in the establishment of infection. In the present study, we demonstrate the involvement of integrin alphavbeta3 (vitronectin receptor) in HIV infection of peripheral blood monocyte-derived macrophages. Culturing monocytes in the presence of M-CSF for 3 days upregulated expression of the alphav-containing integrins, alphavbeta3 and alphavbeta5. The increase in alphavbeta3 expression was accompanied by increased HIV-1 replication by monocytes. Immunoblot analysis showed that purified HIV-gp120 protein interacted with CD4 and alphavbeta3 in immunoprecipitation experiments. Neutralizing antibodies against the alphavbeta3 integrin interfered with the coprecipitation of alphavbeta3 with an anti-gp120 antibody and substantially inhibited HIV infection of monocytes. Neutralizing antibodies against alphavbeta5 or beta1 integrins did not significantly affect HIV infection. These results indicate that HIV infection of primary monocytes requires differentiation of these cells and may involve alphavbeta3 interaction with the HIV-1 envelope protein gp120 for productive infection.

Nonopsonic binding of type III Group B Streptococci to human neutrophils induces interleukin-8 release mediated by the p38 mitogen-activated protein kinase pathway

Nonopsonic interaction of host immune cells with pathogens is an important first line of defense. We hypothesized that nonopsonic recognition between type III group B streptococcus and human neutrophils would occur and that the interaction would be sufficient to trigger neutrophil activation. By using a serum-free system, it was found that heat-killed type III group B streptococci bound to neutrophils in a rapid, stable, and inoculum-dependent manner that did not result in ingestion. Transposon-derived type III strain COH1-13, which lacks capsular polysaccharide, and strain COH1-11 with capsular polysaccharide lacking terminal sialic acid demonstrated increased neutrophil binding, suggesting that capsular polysaccharide masks an underlying binding site. Experiments using monoclonal antibodies to complement receptor 1 and to the I domain or lectin site of complement receptor 3 did not inhibit binding, indicating that the complement receptors used for ingestion of opsonized group B streptococci were not required for nonopsonic binding. Nonopsonic binding resulted in rapid activation of cellular p38 and p44/42 mitogen-activated protein kinases. This interaction was not an effective trigger for superoxide production but did promote release of the proinflammatory cytokine interleukin-8. The release of interleukin-8 was markedly suppressed by the p38 mitogen-activated protein kinase inhibitor SB203580 but was only minimally suppressed by the mitogen-activated protein/extracellular signal-regulated kinase inhibitor PD98059. Thus, nonopsonic binding of type III group B streptococci to neutrophils is sufficient to initiate intracellular signaling pathways and could serve as an arm of innate immunity of particular importance to the immature host.

Interaction of Leishmania gp63 with cellular receptors for fibronectin

The most abundant protein on the surface of the promastigote form of the protozoan parasites Leishmania spp. is a 63-kDa molecule, designated gp63 or leishmanolysin. Because gp63 has been shown to possess fibronectin-like properties, we examined the interaction of gp63 with the cellular receptors for fibronectin. We measured the direct binding of Leishmania to human macrophages or to transfected mammalian cells expressing human fibronectin receptors. Leishmania expressing gp63 exhibited modest but reproducible adhesion to human macrophages and to transfected CHO cells expressing alpha4/beta1 fibronectin receptors. In both cases, this interaction depended on gp63 but occurred independently of the SRYD sequence of gp63, because parasites expressing gp63 with a mutated SRYD sequence bound to macrophages and alpha4/beta1 receptor-expressing cells as well as did wild-type parasites. The contribution of gp63 to parasite adhesion was more pronounced when the assays were performed in the presence of complement, suggesting that the receptors for complement and fibronectin may cooperate to mediate the efficient adhesion of parasites to macrophages. The interaction of gp63 with fibronectin receptors may also play an important role in parasite internalization by macrophages. Erythrocytes to which gp63 was cross-linked were efficiently phagocytized by macrophages, whereas control erythrocytes opsonized with complement alone bound to macrophages but remained peripherally attached to the outside of the cell. Similarly, parasites expressing wild-type gp63 were rapidly and efficiently phagocytized by resting macrophages, whereas parasites lacking gp63 were internalized more slowly. This rapid internalization of gp63-expressing parasites was dependent on the beta1 integrins, because pretreatment of macrophages with monoclonal antibodies to the beta1 integrins decreased the internalization of gp63-expressing parasites. These observations indicate that complement receptors are the primary mediators of parasite adhesion; however, maximal parasite adhesion and internalization may require the participation of the beta1 integrins, which recognize fibronectin-like molecules such as gp63 on the surface of the parasite.

Alkylsilane-modified surfaces: inhibition of human macrophage adhesion and foreign body giant cell formation

A homologous set of alkylsilane-modified glass surfaces with chain lengths ranging from methyl to octadecyl was prepared in order to examine the influence of alkyl surface chemistry on macrophage adhesion and foreign body giant cell (FBGC) formation. Contact angle and X-ray photoelectron spectroscopy analysis confirmed our silanation technique and indicated a consistent alkyl chain density independent of chain length. Human peripheral blood monocytes were isolated and cultured on these alkylsilane surfaces for a period of 10 days. The initial density of human monocytes was similar on all surfaces. Beyond day 0 the clean glass, methyl (DM and C1), propyl (C3), and hexyl (C6) surfaces maintained a high cell density and supported macrophage development. In contrast, long-term macrophage density was extremely low on the tetradecyl (C14) and octadecyl (C18) surfaces. When interleukin-4 was added to induce FBGC formation in vitro, the DM, C1, C3, and C6 surfaces supported high levels of macrophage fusion while clean glass strongly inhibited fusion. The C14 and C18 surfaces did not contain sufficient macrophages to support FBGC formation. Cage implant studies revealed that in vivo macrophage density and FBGC formation on clean glass and C6 surfaces was similar to in vitro data. In contrast to the monocyte culture results, the C18 cage implant samples supported significant FBGC formation, possibly as a result of different conditions within each experimental system. Radiotracer adsorption studies of eight human serum proteins identified the high concentration and tenacious hold of adsorbed von Willebrand factor as being possibly involved in the poor long-term macrophage density observed on C14 and C18.

Determination of a 15437 bp nucleotide sequence around the inhA gene of Mycobacterium avium and similarity analysis of the products of putative ORFs

A 15437 bp region encompassing the inhA locus from the Mycobacterium avium chromosome was cloned and sequenced. From the sequencing data generated and the results of homology searches, the primary structure of this region was determined. This region contains four known genes (acnA, fabG, inhA and hemH) and two genes, invA and invB, whose products display homology with p60 invasion protein of Listeria monocytogenes. Six proteins encoded by putative ORFs contained an RGD motif (often involved in binding to macrophage integrins), while ORF1 and MoxR are probably transcriptional regulators. The rest of the putative products encoded by ORFs in the sequenced region showed little homology with the proteins contained in the databases and were considered to be unknown proteins.

Apoptosis of human monocytes and macrophages by Mycobacterium avium sonicate

Mycobacterium avium is an intracellular organism which multiplies predominantly within human macrophages. This organism has previously been shown to induce apoptosis in human macrophages. With a view to identifying M. avium components that induce cell death in infected host cells, sonicated extracts of M. avium as well as individual components isolated from the M. avium sonicate were tested in various assays with a human monocytic cell line (THP-1). THP-1 cells incubated with M. avium sonicate showed significantly reduced viability after a 2-day exposure compared to control cells incubated with media alone. This effect was dose dependent, with only 6.6% +/- 5.2% and 48.8% +/- 10.3% of the cells being viable by trypan blue exclusion at 600 and 300 microg/ml, respectively. Control cells, on the other hand, exhibited a viability of 98.8% +/- 1.0%. In addition, an 80% ammonium sulfate fraction of the M. avium sonicate and the previously characterized 68-kDa protein were found to have similar effects on THP-1 cells. In both cases, the reduction in viability was due to apoptosis characterized by chromatin condensation, DNA fragmentation by agarose gel electrophoresis, or terminal deoxynucleotidyl transferase-mediated d-UTP nick end labeling (TUNEL) and release of nuclear matrix protein (NMP) into the culture medium. M. avium sonicate-induced apoptosis of THP-1 cells was completely inhibited by the commonly used antioxidants pyrrolidinedithiocarbamate (PDTC) and butylated hydroxyanisole (BHA), indicating that the generation of free oxygen radicals may be responsible for inducing cell death. M. avium sonicate was found to induce apoptosis of monocyte-derived macrophages (MDMs) as well. This effect was not reversed in the presence of PDTC and was not accompanied with DNA fragmentation when determined by agarose gel electrophoresis, as seen in the case of THP-1 cells. However, these MDMs were found to contain fragmented DNA by TUNEL. These findings suggest that the mechanism of cell death in MDMs may be different from that observed with THP-1 cells. Furthermore, these results provide new insight into the effect of M. avium components on host cell responses during M. avium infection.