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Biomedical subjects

C Hammer

Publications and source records attributed to C Hammer.

At least 127 records · Page 7Linked to original sources
PubMed1994

[Autoantibodies against cartilage components: clinical relevance for reconstructive surgery in the area of the head and neck].

The clinical relevance of antibodies against components of cartilage in the reconstructive surgery has not yet been clarified. In our study four groups of patients with successful and unsuccessful autologous cartilage transplantation in rhinosurgery, patients with ear perichondritis and patients with tracheal stenosis after long-term intubation were investigated for the presence of a humoral immune reactivity to cartilage. The control groups consisted of healthy persons and patients with RA. The antibodies against cartilage matrix and chondrocytes were determined using indirect immunofluorescence methods. Patients with unsuccessful cartilage transplantation showed increased antibodies against autologous cartilage (until 1:100) compared to the patients with successful cartilage transplantation. Furthermore, patients suffering from ear perichondritis and tracheal stenosis showed also increased antibodies against cartilage. These data suggest that a humoral immune reactivity against autologous cartilage--independent of an infection--can be one cause for the destruction of cartilaginous tissue.

Adult↗
PubMed1994

[Culture of human cartilage tissue using a perfusion chamber].

In the field of otolaryngology cartilage grafting is commonly performed to reconstruct skeletal defects. Knowledge of chondrocyte growth and differentiation can now be used to engineer cartilage tissue for grafting. The first condition is that chondrocytes maintain their differentiated phenotype besides being able to produce a new cartilage matrix. The target of this study was to develop a three-dimensional culture system for in-vitro formation of vital cartilage transplants. Chondrocytes were isolated by digesting the cartilage matrix with collagenase and hyaluronidase. After embedding in "low-melting" agarose, the chondrocytes were placed into a perfusion culture chamber to provide a constant supply of nutrients to the cultures. The peristaltic pump was operated with on/off intervals of 30 min. Ham's F12 supplemented with 2% FCS and 50 micrograms/ml ascorbic acid was employed as culture medium. Monoclonal antibodies specific to collagens type I and type II were used to characterise cells and matrix synthesis. Synthesis of proteoglycans and collagens was achieved using toluidine blue and azan staining. Under the described culture conditions, the chondrocytes maintained a differentiated phenotype (expression of collagen type II) with synthesis of collagens and proteoglycans. An accumulation of matrix products was achieved pericellularly. After 2-8 weeks the obtained tissue exhibited an excellent histological appearance showing the typical features of cartilage tissue. The results show that the perfusion chamber allows a quick in-vitro fabrication of a piece of pure cartilage tissue for transplantation.

Cartilage↗
PubMed1994

The contribution of endothelial cells to hyperacute rejection in xenogeneic perfused working hearts.

The mechanisms leading to the hyperacute rejection of a vascularized xenograft are still incompletely understood. The first stage of the rejection process is when blood of the recipient comes into contact with the endothelium of the xenograft. A working heart model was used to examine endothelium-related processes and their impact on organ function. Pig hearts were perfused with porcine (autologous) or human (xenogeneic) blood. Cardiac function was evaluated by calculating the stroke work index, arteriovenous oxygen, coronary flow, and resistance. PgF1a as a marker of endothelial activation, its antagonist TXB2, and myoglobin reflecting myocardial damage were measured in the hemoperfusate. H&E and PAS staining and immunohistological demonstration of factor VIII-related antigen was performed. Xenogeneic perfused porcine hearts showed significantly less stroke work, a higher arteriovenous oxygen difference, and an increased coronary resistance. Factor VIII-related antigen could not be demonstrated immunohistologically on the endothelium after xenogeneic perfusion. PgF1a levels were significantly higher in the xenogeneic hemoperfusate, indicating endothelial cell activation. The concentration of myoglobin in the hemoperfusate remained within normal values and was similar during autologous and xenogeneic perfusion. Therefore endothelium-related processes are likely to affect the coronary circulation--thus being one mechanism leading to diminished cardiac performance during hyperacute rejection.

Acute Disease↗
PubMed1994

Xenogeneic ex vivo hemoperfusion of rhesus monkey livers with human blood.

In order to copy the clinical situation of concordant xenotransplantation, Rhesus Monkey livers were hemoperfused with human blood. Changes of immunological (TNFalpha, IL-1beta, IL-2, IL-2R, IL-6, IFNgamma, TXB2, 6kPGF1alpha, sICAM-1, sELAM-1, sHLA-I-Ag) and pathophysiological (GOT, GPT, LDH, CK) parameters were followed. Our experiment proves that all phenomena start in the first hour of xenogeneic blood circulation. Xenogeneic rejection in our concordant system is surprisingly severe. Preformed natural antibodies only cannot be the reason of such a damage. We think that beside other important immunological mechanisms, humoral mediators play a considerable role at the beginning of a xenogeneic rejection.

Animals↗
PubMed1994

Production of proinflammatory cytokines and adhesion molecules in ex-vivo xenogeneic kidney perfusion.

Xenogeneic transplantation of solid organs is limited due to hyperacute rejection. In concordant systems, the mechanisms of rejection can be studied due to cross-reactivity of mediators with anti-human monoclonal antibodies. The aim of this study was to obtain information about the kinetics of proinflammatory cytokines and production of soluble adhesion molecules in the acute phase of reperfusion, eight kidneys from rhesus monkeys were perfused ex-vivo with human blood (group B/0) for 1 hour in a closed system. Blood levels of IL-1b, IL-6, TNFalpha, soluble ICAM, and E-selectin were measured using an ELISA technique under steady-state conditions. Cytokine levels rose significantly within the 60-min interval (IL-1b, 6.1 +/- 2.6-161.1 +/- 98.5 pg/ml; IL-6, 30.2 +/- 7.7-274.2 +/- 75.8 pg/ml; TNFalpha, 544.2 +/- 363.6-1651.0 +/- 25.7 pg/ml; P < 0.05). Immediately after the beginning of reperfusion, soluble ICAM-1 and selectin levels were abnormally high and rose constantly throughout the observation period, reaching significance at 60 min. High levels of proinflammatory cytokines may lead to an induction of adhesion molecules, thus, upregulating the leukocyte-endothelial interaction in a complement-independent mechanism. Specific pretreatment with monoclonal antibodies against ICAM-1, LFA-1, or other soluble mediators may be useful in down-regulating hyperacute rejection in trans-species transplantation.

Animals↗
PubMed1994

Antigen presenting cell function of class II positive human nasal chondrocytes.

It is postulated that class II positive chondrocytes may be actively involved in the destruction or rejection of vital transplanted cartilage grafts. To investigate whether human nasal chondrocytes may also function as accessory cells in ongoing immune reactions with cartilage destruction, mixed leukocyte-chondrocyte cultures and antigen presentation assays were performed. Freshly isolated HLA class II antigen negative chondrocytes obtained from nasal septa were not stimulatory to autologous resting T lymphocytes. HLA class II positive chondrocytes treated with gamma-interferon were able to present antigens to autologous activated T cells derived from an antigen (tetanus) specific T cell line. Upon incubation with activated T cells, initially class II negative changed their phenotype resulting in the expression of class II antigens and enabling them to effectively present antigen. These results suggest an active role of chondrocytes in the rejection of cartilage grafts.

Antigen-Presenting Cells↗
PubMed1994

Expression of ICAM-1 on isolated human nasal, auricular and costal chondrocytes.

Expression of intercellular adhesion molecule-1 (ICAM-1) on targets has been reported to be a relevant factor for leukocyte migration, adhesion and function. Because stimulated chondrocytes have been shown to express molecules of immunological import (like HLA class II antigens) and because rejected or resorbed cartilage grafts used in the field of ENT are often characterized by adjacent infiltrating leukocytes, the presence of ICAM-1 on human nasal, auricular and costal cartilage was investigated. For this study, cartilage tissue sections and chondrocytes in suspension as well as cultured chondrocytes were prepared. Specific monoclonal antibodies (mAb) were used for immunocyto- and immunohistochemical Alkaline-Phosphatase-anti-Alkaline-Phosphatase staining (APAAP staining) as well as for flow cytometry analysis. ICAM-1 on healthy cartilage tissue sections was not found. On the other hand, both chondrocytes freed from matrix and cultured chondrocytes showed strongly positive staining patterns for ICAM-1. This result was obtained for chondrocytes from nasal, auricular as well as costal cartilage. This observed expression of ICAM-1 on chondrocytes with defective extracellular matrix demonstrates that cartilage cells are able to synthesize ICAM-1 without any paracrine stimulus from non-chondrocyte cells. It suggests that ICAM-1 plays a role in processes where tissue damage leads to the exposure of chondrocyte surfaces. Therefore, ICAM-1 expression on chondrocytes may also be a factor in destructive cartilage graft resorption.

Antibodies, Monoclonal↗
PubMed1994

Effect of growth factors on cell proliferation by human nasal septal chondrocytes cultured in monolayer.

In the field of reconstructive surgery, autologous cartilage grafting is commonly performed to reconstruct skeletal defects. Because of the limited supply of fresh autologous cartilage many investigators concentrate on in vitro production of cartilage tissue. Several growth factors regulate the metabolism and activation of cartilage cells. In order to enhance the culture conditions for cartilage cells, the aim of our investigations was to characterize the influence of transforming growth factor (TGF)-beta, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) on the proliferation of differentiated human nasal septal chondrocytes. The isolated cells were cultured in monolayer using DMEM with and without 10% FCS. The cell proliferation was assessed using tritiated thymidine. We measured an increase of the proliferation rates when the different growth factors were added. The most important stimulatory effect was due to bFGF and the less to EGF. If all growth factors were added together a fivefold increase in the proliferative activity of the cells was achieved. The effects were further enhanced by factors present in fetal calf serum. We conclude that the culture conditions for cell expansion for cartilage engineering can be optimized employing growth factors.

Adult↗
PubMed1994

Bone formation in coralline hydroxyapatite. Effects of pore size studied in rabbits.

We analyzed osseous reactions in the rabbit femoral condyle to coralline hydroxyapatite bone substitutes of various pore sizes by radiology and histology. The results were compared to bone repair of empty cavities and to integration of allografts. Spontaneous bone repair of the empty cavities took approximately 12 weeks, while integration of the cryopreserved allografts occurred after 9 weeks. However, no signs of new bone formation were found with the 200 microns pore size hydroxyapatite. In contrast, there was substantial production of bone within the 500 microns pore size implants at 12 and 26 weeks. Our results indicate that the pore size of the coralline hydroxyapatite influenced the development of bone in the implants in the cancellous bone bed of the rabbit femoral condyle. The results also show that spontaneous bone repair should be taken into consideration when the integration of implants is evaluated.

Animals↗
PubMed1994

Xenotransplantation--is it just around the corner?

Xenotransplantation will certainly solve the problem of the allogeneic organ shortage if long-term organ function can be achieved. Acceptance or rejection of the grafts depend not only on immunological mechanism but, as already recognized in chronic rejection (i.e. transplant atherosclerosis), on many other biochemical, physiological, and even morphological characteristics including inflammatory events originating from infections. The way in which signals in the form of hormones, neurotransmitters, enzymes and growth factors are translated in xenogeneic systems has not received adequate attention, if any at all. Central questions still to be answered are, how many xenogeneic hormonal and enzymatical interactions are possible? Are they able to maintain the metabolism in a foreign organ or body and for how long? In addition, transport molecules, the most important of which is albumin, must be considered when trying to achieve long-term survival using organs from a widely divergent species. Large quantities of foreign proteins, mediators and enzymes are released into the circulation when, for example, xenogeneic livers or other organs suffer from hyperacute rejection. The function of the liberated enzymes, hormones and inhibitors is far from being understood or even investigated. The amount of potassium released from a deteriorating xenogeneic liver is able to mimic a sometimes lethal cardioplegic solution. The first data coming from intravital microscopy herald that adhesion molecules, the newest but not last in the line of troubleshooters, interact with interleukins and eicosanoids and play a major role in the regulation of microcirculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Xenogeneic ex vivo hemoperfusion of rhesus monkey livers with human blood.

This model of completely isolated ex vivo hemoperfused RM livers reflects immunologic effects of donor organs and the humoral blood components of the recipient. The reaction between the isolated organ and recirculating blood allows us to concentrate on effects and products liberated under such a selected but limited situation. The slight influence of used materials on the monitored parameters in the circuit is of no importance. The massive release of TNF alpha, IL-1 beta, IL-6, IFN gamma, and 6kPGF1 alpha between 15 and 60 minutes after reperfusion was the specific result of xenoperfusion. IL-2 increases after 60 minutes. Soluble human IL-2R seems to be eliminated from the perfusate by the RM liver to about 50% of initial values. It increases again sharply beyond 180 minutes now originating from the RM liver. During the whole perfusion time, soluble HLA-I antigen and the detected adhesion molecules decrease to 50% of their initial values.

Animals↗
PubMed1994

Fundamental problems of xenotransplantation.

Xenogeneic transplantation of organs will certainly solve the problem of organ shortage if it succeeds in long term function of the xenografts. Accommodation and rejection of the grafts depend however not only on the immunological mechanisms but, as already recognized in chronic rejection i.e. transplant atherosclerosis, in many other biochemical and physiological, even morphological characters including inflammatory events originating from infections. Preformed natural antibodies, an important part of the preimmunitary system turn again out to be a lock with seven seals. With increasing amounts of data the confusion about possibly an epiphenomenom in xenotransplantation becomes complete. Complement developed by nature before immunoglobulins can be activated by many ways--inducing a series of cascades like cell lysis, blood clotting, cell adherence and liberation of oxygen radicals. Large amounts of foreign proteins are released in the circulation when for example xenogeneic livers or other organs suffer from hyper acute rejection. The function of the liberated enzymes, hormones and inhibitors is far from being understood or even investigated. The amount of potassium released from a deteriorating liver is able to mimic a sometimes lethal cardioplegic situation. First data coming from intra vital microscopy herald that adhesion molecules, the newest but not last in line of trouble shooters play together with integrins and interleukins and eicosanoids a major role in microcirculation, be it as falsely activated system or as incompatible system not able to protect from the attack of white blood cells, their adhesion and migration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Hyperacute rejection in an ex vivo model of renal xenografting. Role of the mediator response and its pharmacologic manipulation by the specific platelet-activating factor antagonist WEB 2086BS.

The pharmacologic modulation of the platelet-activating factor antagonist WEB 2086BS on the release of metabolites of the arachidonic acid and the cytokine TNF alpha was investigated in an ex vivo xenograft model of hyperacute rejection. Pig kidneys were perfused for 60 min in a perfusion system with oxygenated heparinized human or autologous porcine blood, respectively. During autologous perfusion, no alterations in the mediator response could be detected, whereas xenogeneic perfusion induced progressive release of mediators. Treatment by the platelet-activating factor antagonist WEB 2086BS resulted in a significantly reduced liberation of the cytokine TNF alpha and of prostanoids. The histological findings verified that a hyperacute rejection in the xenogeneic perfused organs had occurred, which was mitigated by the treatment with WEB 2086BS. This observation confirms that inflammatory mediators play a decisive role in hyperacute xenogeneic rejection. The results suggest that suppression or manipulation of mediator-specific tissue receptors by receptor-antagonists could be an additional therapeutic mode to control hyperacute rejection in xenogeneic transplantation.

Adult↗
PubMed1993

A critical analysis of human immunodeficiency virus transmission using human cartilage allografts.

Allogeneic cartilage represents an important source of tissue for reconstructive surgery in the head and neck. The use of allografts is now being discussed because of the possible transmission of the human immunodeficiency virus (HIV). The receptor for HIV in most cell types is the CD-4 molecule. Since cartilage is a popular homograft source, the purpose of this study was to investigate the presence of CD-4 molecules on cartilage tissue as detected with an immunoperoxidase staining and immunofluorescence flow cytometric analysis using a monoclonal antibody. Our results indicate clearly the absence of the HIV receptor on human cartilage tissue. We have concluded therefore that normal cartilage tissue cannot be infected by HIV, at least not through a CD-4-dependent mechanism.

CD4 Antigens↗