Use of a bovine model to study the role of adhesion molecule CD11/CD18 in hemodialysis-induced neutropenia

Complement activation on poly(ethylene oxide)-like radiofrequency glow discharge-deposited surfaces

Nonspecific protein adsorption, particularly fibrinogen (Fg), is thought to be an initiating step in the foreign body response (FBR) to biomaterials by promoting phagocyte attachment. In previous studies, we therefore prepared radiofrequency glow discharge (ethylene oxide)-like tetraglyme (CH(3)O(CH(2)CH(2)O)(4)CH(3)) coatings adsorbing <10 ng/cm(2) Fg and showed that they had the expected low monocyte adhesion in vitro. However, when these were implanted in vivo, many adherent inflammatory cells and a fibrous capsule were found, suggesting the role of alternative proteins, such as activated complement proteins, in the FBR to these materials. We therefore investigated complement interactions with the tetraglyme surfaces. First, because of its well-known role in complement C3 activation, we measured the hydroxyl group (-OH) content of tetraglyme, but found it to be low. Second, we measured C3 adsorption to tetraglyme from plasma. Low amounts of C3 adsorbed on tetraglyme, although it displayed higher binding strength than the control surfaces. Finally, complement activation was determined by measuring C3a and SC5b-9 levels in serum after incubating with tetraglyme, as well as other surfaces that served as positive and negative controls, namely poly(vinyl alcohol) (PVA) hydrogels, Silastic sheeting, and poly(ethylene glycol) self-assembled monolayers with different end groups. Despite displaying low hydroxyl group concentration, relatively high C3a and SC5b-9 levels were found in serum exposed to tetraglyme, similar to the values in our positive control, PVA. Our results support the conclusion that complement activation by tetraglyme is a possible mechanism involved in the FBR to these biomaterials.

Donor antibodies to HNA-3a implicated in TRALI reactions prime neutrophils and cause PMN-mediated damage to human pulmonary microvascular endothelial cells in a two-event in vitro model

Transfusion-related acute lung injury (TRALI) is the leading cause of transfusion-related mortality. Antibodies to HNA-3a are commonly implicated in TRALI. We hypothesized that HNA-3a antibodies prime neutrophils (PMNs) and cause PMN-mediated cytotoxicity through a two-event pathogenesis. Isolated HNA-3a+ or HNA-3a- PMNs were incubated with plasma containing HNA-3a antibodies implicated in TRALI, and their ability to prime the oxidase was measured. Human pulmonary microvascular endothelial cells (HMVECs) were activated with endotoxin or buffer, HNA-3a+ or HNA-3a- PMNs were added, and the coculture was incubated with plasma+/-antibodies to HNA-3a. PMN-mediated damage was measured by counting viable HMVECs/mm2. Plasma containing HNA-3a antibodies primed the fMLP-activated respiratory burst of HNA-3a+, but not HNA-3a-, PMNs and elicited PMN-mediated damage of LPS-activated HMVECs when HNA-3a+, but not HNA-3a-, PMNs were used. Thus, antibodies to HNA-3a primed PMNs and caused PMN-mediated HMVEC cytotoxicity in a two-event model identical to biologic response modifiers implicated in TRALI.

Haemodialysis-induced pulmonary granulocyte sequestration in rabbits is organ specific

BACKGROUND

Haemodialysis (HD) with cuprophan (CU) dialysers leads to a severe transient granulocytopenia. In the present study, we challenge the hypothesis that granulocytes sequester within the pulmonary vasculature simply because this is the first vascular bed encountered. This hypothesis is based upon experiments in which activated plasma or complement fragments were infused into animals, and may not pertain to the more complex HD situation.

METHODS

We used a rabbit model of HD, and returned the blood into the caval vein (v-HD) or aorta (a-HD). The mesentery was continuously monitored by intravital video microscopy, whereas other tissues were collected at the nadir of granulocytopenia and analysed immunohistochemically.

RESULTS

Compared with controls, the number of granulocytes within alveolar walls was almost 2-fold higher following HD, with no difference between venous and arterial blood return. In addition, both v-HD and a-HD induced granulocyte accumulation within part of the larger pulmonary microvessels, though the amount of granulocytes found was 2-fold higher after v-HD. At no time did a-HD induce granulocyte sequestration within the mesenteric microcirculation. Neither did arterial return increase their number in other first-pass tissues like skeletal muscle or renal glomeruli, but it did so in the liver. In the heart, granulocyte content decreased during HD.

CONCLUSIONS

Pulmonary sequestration of granulocytes during CU HD is not simply a first-pass effect, but is organ specific to a great extent. The accumulation within larger microvessels suggests an important role for adhesion molecules, whereas cellular stiffening may be involved in granulocyte retention within alveolar capillaries.