Activation of macrophages in an experimental rat model of arthritis induced by Erysipelothrix rhusiopathiae infection

Pathology, microbiology, and genetic diversity associated with Erysipelothrix rhusiopathiae and novel Erysipelothrix spp. infections in southern sea otters (Enhydra lutris nereis)

Erysipelothrix spp., including E. rhusiopathiae, are zoonotic bacterial pathogens that can cause morbidity and mortality in mammals, fish, reptiles, birds, and humans. The southern sea otter (SSO; Enhydra lutris nereis) is a federally-listed threatened species for which infectious disease is a major cause of mortality. We estimated the frequency of detection of these opportunistic pathogens in dead SSOs, described pathology associated with Erysipelothrix infections in SSOs, characterized the genetic diversity and antimicrobial susceptibility of SSO isolates, and evaluated the virulence of two novel Erysipelothrix isolates from SSOs using an in vivo fish model. From 1998 to 2021 Erysipelothrix spp. were isolated from six of >500 necropsied SSOs. Erysipelothrix spp. were isolated in pure culture from three cases, while the other three were mixed cultures. Bacterial septicemia was a primary or contributing cause of death in five of the six cases. Other pathology observed included suppurative lymphadenopathy, fibrinosuppurative arteritis with thrombosis and infarction, bilateral uveitis and endophthalmitis, hypopyon, petechia and ecchymoses, mucosal infarction, and suppurative meningoencephalitis and ventriculitis. Short to long slender Gram-positive or Gram-variable bacterial rods were identified within lesions, alone or with other opportunistic bacteria. All six SSO isolates had the spaA genotype-four isolates clustered with spaA E. rhusiopathiae strains from various terrestrial and marine animal hosts. Two isolates did not cluster with any known Erysipelothrix spp.; whole genome sequencing revealed a novel Erysipelothrix species and a novel E. rhusiopathiae subspecies. We propose the names Erysipelothrix enhydrae sp. nov. and Erysipelothrix rhusiopathiae ohloneorum ssp. nov. respectively. The type strains are E. enhydrae UCD-4322-04 and E. rhusiopathiae ohloneorum UCD-4724-06, respectively. Experimental injection of tiger barbs (Puntigrus tetrazona) resulted in infection and mortality from the two novel Erysipelothrix spp. Antimicrobial susceptibility testing of Erysipelothrix isolates from SSOs shows similar susceptibility profiles to isolates from other terrestrial and aquatic animals. This is the first description of the pathology, microbial characteristics, and genetic diversity of Erysipelothrix isolates recovered from diseased SSOs. Methods presented here can facilitate case recognition, aid characterization of Erysipelothrix isolates, and illustrate assessment of virulence using fish models.

Loosening and osteolysis of cemented joint arthroplasties. A biologic spectrum

The purpose of this study was to characterize the cell types (using immunohistochemistry) and cytokine expression (using in situ hybridization) of tissues surrounding well fixed and loose cemented prostheses undergoing revision. Clinical and radiographic data were gathered prospectively for a series of cemented total joint replacements undergoing revision. Three groups were identified: (1) loose implants with osteolysis (10 specimens), (2) loose implants without osteolysis (11 specimens), and (3) well fixed implants (7 specimens). At surgery, a specimen was harvested from the bone cement interface. Immunohistochemical staining was performed using monoclonal antibodies to identify macrophages and lymphocyte subgroups. Human antisense probes were selected to identify the mRNA for specific cytokines using in situ hybridization. The percentage of positively staining cells was determined for each antibody or probe using a grid counting technique. Tissues from loose cemented prostheses with osteolysis contained significantly greater numbers of macrophages and T lymphocytes compared with tissues from loose and well fixed cemented prostheses without osteolysis. The number of interleukin-1 and interleukin-6 positive cells was highest in specimens with osteolysis and lowest in specimens from well fixed prostheses. These cytokines modulate the growth and differentiation of cells in the immune system and the monocyte and macrophage system and mediate the remodeling of bone and mesenchymal tissues. Specific cell populations and cytokine profiles appear to be involved in periprosthetic osteolysis; this information may be useful in planning strategies for prevention and treatment.

Suppressor macrophages mediate depressed lymphoproliferation in chickens infected with avian reovirus

A previous study indicated that spleens from reovirus-infected chickens contained macrophages that were primed to produce nitric oxide (NO). The presence of these primed macrophages correlated with depressed in vitro T cell mitogenesis. The current studies indicated that splenic adherent macrophages from virus-exposed chickens inhibited concanavalin A (ConA) induced proliferation of normal spleen cells. ConA-stimulated spleen cells from uninfected chickens, but not virus-exposed chickens, produced large quantities of interleukin-2 (IL-2) and a factor that induced NO production. This factor was tentatively named NO inducing factor (NOIF). The removal of macrophages from the spleens of virus-exposed chickens by plastic adherence resulted in partial recovery of ConA-induced proliferation and the production of normal levels of IL-2 and increased levels of NOIF, although these remained below normal. However, nonadherent spleen cells produced substantial quantities of NO, which indicated an incomplete removal of macrophages. Because removal by plastic adherence did not result in the depletion of all macrophages, spleen cells were panned with anti-CD3 antibody to obtain an almost pure population of T cells. Fractionated T cells from virus-exposed chickens proliferated vigorously to ConA and produced normal levels of IL-2 and NOIF. When splenic adherent cells from virus-exposed chickens were added to purified T cells, the T cells failed to respond to ConA. Addition of splenic adherent cells from virus-free chickens did not induce mitogenic inhibition. Further, the addition of purified T cells from the spleens of reovirus-infected chickens to T cells from virus-free birds did not adversely affect T cell mitogenesis. These data indicated that reovirus infection in chickens does not compromise the functional capabilities of T cells but induces suppressor macrophages that inhibit T cell functions.

Influence of soluble suture factors on in vitro macrophage function

Suture materials may interact with immune competent cells and thereby affect localized immunity. Macrophages are central to the inflammatory response and coordinate wound healing. They are also involved in the clearance of foreign material, bacteria and malignant cells. We studied the influence of soluble factors associated with silk, steel, nylon, polyglactin, polydioxanone and chromic catgut sutures on macrophage adherence, phagocytosis and the production of lysozyme and tumour necrosis factor. Soluble factors from suture materials influenced macrophage behaviour in vitro causing cellular activation, functional impairment and alterations in secreted levels of the cytokine tumour necrosis factor and the bactericidal agent lysozyme. Of the six materials studied, polyglactin had the most extreme effect, causing significant inhibition of cell adherence and lysozyme production. Silk also exerted a considerable effect on macrophages, significantly inhibiting adherence. In contrast, steel and polydioxanone media caused minimal inhibition of macrophage function although, as with all materials, they did activate the cells. This study has demonstrated that sutures release immunotoxic factors which considerably influence macrophage behaviour in vitro. These effects may have important clinical implications.

The effects of micromotion and particulate materials on tissue differentiation. Bone chamber studies in rabbits

Motion at the interface between bone and implants for joint replacement may interfere with osseointegration and prosthesis stabilization. Particulate materials may cause foreign body and chronic inflammatory reactions resulting in bone resorption (osteolysis). The micromotion chamber (MC) and the bone harvest chamber (BHC) were implanted in the rabbit tibia, and the effects of micromotion and phagocytosable particulate materials on tissue formation within the chamber were assessed by studying bone ingrowth into a 1-mm pore. Using the MC, one short daily episode of motion (20 cycles/day, 0.5 mm amplitude) for three weeks decreased the amount of bone ingrowth. Using a different pore configuration, the same parameters of motion increased bone ingrowth. Increasing the amplitude of motion (from 0.5 to 0.75 mm), or the number of daily motion periods (from one to two per day) then decreased bone ingrowth. These studies suggest the existence of a window of externally applied strain: a small stimulus may facilitate and a large stimulus may discourage bone formation within the chamber. Cessation of a given set of motion parameters (producing primarily fibrous tissue) for an additional three weeks was accompanied by tissue differentiation into bone. Using the BHC, small, phagocytosable particles of bone cement, high density polyethylene and cobalt chrome alloy, at a concentration of 1.0 x 10(8) particles/mL, caused a foreign body reaction and inhibited the ingrowth of bone. Particles of titanium alloy had no effect on net bone formation. In studies using normal and immunodeficient rats, T lymphocytes were not a prerequisite for macrophages to phagocytose polyethylene particles. In the clinical situation, micromotion and particulate debris may be synergistic in producing prosthetic loosening. If an implant does not undergo osseointegration due to excessive micromotion, the fibrous tissue interface may provide a conduit for the subsequent migration of particles around the implant.

T-lymphocytes are not necessary for particulate polyethylene-induced macrophage recruitment. Histologic studies of the rat tibia

Immunological processes involving T-lymphocytes have been implicated in the mechanisms of aseptic loosening of joint endoprostheses. We report the histological reaction of bone to phagocytosable particles of high-density polyethylene (HDPE) in normal and T-cell deficient rats. A bolus of 3 x 10(7) polyethylene particles averaging 4.7 microns in size, mixed in 0.1 mL of sodium hyaluronate, was injected into the right proximal tibia of 10 normal and 10 T-cell deficient (nude) Rowett rats from the same litter. The left control side was injected with sodium hyaluronate alone. The animals were killed after 6 weeks. Transverse paraffin-embedded sections stained with hematoxylin and eosin were made of the implant area. On the control side, there was normal bone marrow without evidence of foreign body reaction. On the HDPE side, in both normal and T-cell deficient rats, macrophages were found to surround and engulf the particles, with no differences in the histological reactions. We conclude that T-lymphocytes are not necessary for the recruitment of macrophages to sites in which phagocytosable particles of HDPE have been implanted.

Sensitization of rat alveolar macrophages to enhanced TNF-alpha release by in vivo treatment with dexamethasone

Treatment of rats with dexamethasone rapidly induced a marked weight loss which occurred within 3 days and persisted for several weeks. The cachectic state was paralleled by increased serum levels of triglycerides, albumin, and protein and a strong reduction of blood mononuclear leukocytes. In lung sections, an increased number of mononuclear giant cells was found but no bacteria, fungi, or Pneumocystis carinii organisms. Quite strikingly, alveolar macrophages from dexamethasone-treated rats, but not from control animals, were highly sensitive to LPS and released large amounts of TNF-alpha ex vivo. Also under in vivo conditions, high TNF-alpha serum concentrations were found in dexamethasone-treated but not control rats when examined 1 1/2 hr after an intravenous LPS injection. These data suggest that the glucocorticoid-induced cachexia of rats may be linked, at least in part, to readily inducible TNF-alpha release from primed macrophages.

Detection of cytokine activated chondrocytes in arthritic joints from pigs infected with Erysipelothrix rhusiopathiae

Chronic polyarthritis was induced in pigs by injection of Erysipelothrix rhusiopathiae and the in vivo activation of chondrocytes by cytokines was then investigated in the affected joints by immunocytochemistry. A polyclonal antiserum which recognises surface markers on in vitro interleukin 1 activated porcine chondrocytes was used to detect activated chondrocytes in all zones of the cartilage from diseased joints. In contrast, cartilage removed from an unaffected joint in the same animal showed no chondrocyte activation. Inflammatory synovial tissue removed from diseased joints and cocultured with cartilage from the unaffected joint induced activation of adjacent chondrocytes. The presence of interleukin 1 in the inflammatory cells of the synovium was confirmed and major histocompatibility complex (MHC) class II antigens were detected as a marker of synovial activation. Chondrocytes were found not to express class II antigens in cartilage from either the diseased or the unaffected joint. These observations show that the porcine erysipelas model of arthritis will be useful in facilitating a novel approach to monitoring the behaviour of individual chondrocytes under pathophysiological conditions.

Experimental animal models resembling rheumatoid arthritis

The experimental animal models of arthritis which in certain aspects share similarities to human rheumatoid arthritis are reviewed. Various methods have been applied to induce in animals experimental models of arthritis which would provide important insights into the aetiopathogenetic mechanisms of human RA. Immunological methods and infectious agents induced the most interesting models. The histology of the synovial tissue, regardless of the inducing mechanisms, is similar to the lesions of RA. Yet, none of these experimental models of arthritis reflects all the articular and systemic features, the immunological profile and the genetic factors which characterize the human disease. The animal models of arthritis reported here and the development of new ones may ultimately offer the information necessary for the understanding of the mechanisms involved in the aetiopathogenesis of human rheumatoid disease.

Monoclonal antibodies preventing the development of polyarthritis in rats induced by experimental infection with erysipelas bacteria

Monoclonal IgM-antibodies specific for arthritogenic erysipelas bacteria (Erysipelothrix rhusiopathiae, serovar 2, strain T28) were isolated from rats suffering from erysipelas polyarthritis. Four of them (C52, D9, E51, R117) were administered to syngeneic Lewis rats. While D9 and an unrelated rat-IgM-antibody showed no effect, C52 protected partially and R117 as well as E51 fully from all symptoms of erysipelas polyarthritis. Prevention of the disease was associated with a lack of antibody-formation against the erysipelas bacteria. There is evidence that prevention is not due to classical passive immunization, but rather to induction of host mechanisms efficiently activated by "inductive" monoclonal antibodies.

Characterization of a protective protein antigen of Erysipelothrix rhusiopathiae

Although vaccination is widely practiced against infection by Erysipelothrix rhusiopathiae in pigs and turkeys, the protective antigen(s) involved have not been fully characterized or purified to homogeneity. Antigens of E. rhusiopathiae strain T28, serotype 2b, and of FRANKFURT XI, serotype N, in culture supernatant and in extracts made with hot acid, 10 mM NaOH, ultrasound or EDTA were compared by SDS-PAGE and immunoblotting and in a mouse protection test. EDTA and 10 mM NaOH yielded highly protective extracts; culture supernatant was less protective and ultrasonic or hot acid extracts stimulated little or no protection in mice. Protective antisera from swine, horses and mice recognized prominent bands of molecular mass (m.m.) of 66-64 and 40-39 kDa in EDTA and 10 mM NaOH extracts. Mice immunized with preparations of the 66-64 kDa band purified by preparative electrophoresis were protected. Both antigens were trypsin sensitive, contained no detectable polysaccharide, and showed a marked tendency to aggregate in the absence of SDS.

Enhancement of tumor necrosis factor-alpha gene expression by low doses of prostaglandin E2 and cyclic GMP

Macrophage-derived PGE2 is usually considered to be a down-regulator of TNF-alpha production. However, we recently demonstrated that PGE2 may display dual activities in that low concentrations stimulated whereas higher doses suppressed TNF-alpha synthesis in resident peritoneal macrophages. To examine the underlying molecular mechanisms, we studied TNF-alpha gene expression in rat peritoneal macrophages and the murine PU5-1.8 macrophage line. In both macrophage types, PGE2 enhanced TNF-alpha gene transcription and production at an optimal concentration of 1 ng/ml. Furthermore, evidence was obtained that PGE2 may stimulate TNF-alpha mRNA accumulation via a rise of the intracellular messenger cGMP. Both, exogenously added as well as endogenously, by sodium nitroprusside generated cGMP were found to enhance TNF-alpha gene expression and production. These findings lend further support to the concept that cGMP may represent one of the positive signals for TNF-alpha synthesis.