Routine colonoscopy is not required in uncomplicated diverticulitis: a systematic review.

BACKGROUND: It is generally accepted that patients following an episode of diverticulitis should have additional colonoscopy screening to rule out a colorectal malignancy. We aimed to investigate the rate of CRC found by colonoscopy after an attack of uncomplicated diverticulitis. METHODS: MEDLINE, Embase, and Cochrane databases were searched systematically for clinical trials or observational studies on colonic evaluation by colonoscopy after the initial diagnosis of acute uncomplicated diverticulitis, followed by hand-searching of reference lists. RESULTS: Nine studies met the inclusion criteria and included a total number of 2,490 patients with uncomplicated diverticulitis. Subsequent colonoscopy after an episode of uncomplicated diverticulitis was performed in 1,468 patients (59%). Seventeen patients were diagnosed with CRC, having a prevalence of 1.16% (95% confidence interval 0.72-1.9% for CRC). Hyperplastic polyps were seen in 156 patients (10.6%), low-grade adenoma in 90 patients (6.1%), and advanced adenoma was reported in 32 patients (2.2%). CONCLUSION: Unless colonoscopy is regarded for screening in individuals aged 50 years and older, routine colonoscopy in the absence of other clinical signs of CRC is not required.

Influence of isomalto-oligosaccharides on intestinal microbiota in rats.

AIMS: Isomalto-oligosaccharides (IMO) with α(1 --> 6) and α(1 --> 4) glucosidic linkages are produced by enzymatic conversion of starch. IMO are only partially digestible but data on their influence on intestinal microbiota are limited. It was the aim of this study to investigate the effect of IMO diet on intestinal microbiota and short-chain fatty acids production (SCFA) in rats. METHODS AND RESULTS: Three groups of F344 rats, each consisting of six animals, were fed IMO, inulin or a control diets for six weeks. A qualitative assessment of the intestinal microbiota was achieved by PCR-denaturing gradient gel electrophoresis (DGGE). Major bacterial taxa were quantified by quantitative PCR (qPCR), and SCFA were measured using gas chromatography. Quantitative PCR demonstrated that lactobacilli were one of the dominant bacterial taxa in faecal samples from rats. IMO increased the number of lactobacilli and the total number of intestinal bacteria in rats fed IMO compared with animals receiving control and inulin diets. Furthermore, PCR-DGGE with lactobacilli-specific primers showed an altered biodiversity of lactobacilli in rats fed IMO compared with control diet. CONCLUSIONS: IMO selectively stimulates lactobacilli and increases their diversity in rats. SIGNIFICANCE AND IMPACT OF STUDY: Isomalto-oligosaccharides specifically stimulate growth of intestinal lactobacilli in a rat model system.

An imbalance in mucosal cytokine profile causes transient intestinal inflammation following an animal's first exposure to faecal bacteria and antigens.

Intestinal microflora play a critical role in the initiation and perpetuation of chronic inflammatory bowel diseases. In genetically susceptible hosts, bacterial colonization results in rapid-onset chronic intestinal inflammation. Nevertheless, the intestinal and systemic immune response to faecal bacteria and antigen exposure into a sterile intestinal lumen of a post-weaned animal with a mature immune system are not understood clearly. This study examined the effects of faecal bacteria and antigen exposure on the intestinal mucosal and systemic immune system in healthy axenic mice. Axenic wild-type mice were inoculated orally with a crude faecal slurry solution derived from conventionally raised mice and were analysed prior to and then at days 3, 7, 14 and 28 post-treatment. Ingestion of faecal slurry resulted in a transient, early onset of proinflammatory interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-17 response that was maximal at day 3. In contrast, the transient release of the anti-inflammatory cytokines IL-10 and IL-4 occurred later and was maximal at day 7. Both responses subsided by day 14. This early cytokine imbalance was associated with a brief rise in colonic and caecal histopathological injury score at day 7. The bacterial antigen-specific systemic response was found to follow the intestinal immune response with a maximal release of both pro- and anti-inflammatory cytokines at day 7. Thus, first exposure of healthy axenic wild-type mice to normal faecal flora and antigens results in an early proinflammatory cytokine response and transient colonic inflammation that then resolves in conjunction with a subsequent anti-inflammatory cytokine profile.

Prophylactic ciprofloxacin treatment prevented high mortality, and modified systemic and intestinal immune function in tumour-bearing rats receiving dose-intensive CPT-11 chemotherapy.

Infectious complications are a major cause of morbidity and mortality from dose-intensive cancer chemotherapy. In spite of the importance of intestinal bacteria translocation in these infections, information about the effect of high-dose chemotherapy on gut mucosal immunity is minimal. We studied prophylactic ciprofloxacin (Cipro) treatment on irinotecan (CPT-11) toxicity and host immunity in rats bearing Ward colon tumour. Cipro abolished chemotherapy-related mortality, which was 45% in animals that were not treated with Cipro. Although Cipro reduced body weight loss and muscle wasting, it was unable to prevent severe late-onset diarrhoea. Seven days after CPT-11, splenocytes were unable to proliferate (stimulation index=0.10+/-0.02) and produce proliferative and inflammatory cytokines (i.e., Interleukin (IL)-2, interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) IL-1beta, IL-6) on mitogen stimulation in vitro (P<0.05 vs controls), whereas mesenteric lymph node (MLN) cells showed a hyper-proliferative response and a hyper-production of pro-inflammatory cytokines on mitogen stimulation. This suggests compartmentalised effects by CPT-11 chemotherapy on systemic and intestinal immunity. Cipro normalised the hyper-responsiveness of MLN cells, and in the spleen, it partially restored the proliferative response and normalised depressed production of IL-1beta and IL-6. Taken together, Cipro prevented infectious challenges associated with immune hypo-responsiveness in systemic immune compartments, and it may also alleviate excessive pro-inflammatory responses mediating local gut injury.

Review and clinical perspectives for the use of infliximab in ulcerative colitis.

Infliximab is a chimeric, monoclonal anti-tumour necrosis factor-alpha antibody. It has been previously demonstrated to be an effective treatment for patients with Crohn's disease who do not achieve the desired response with conventional treatments. Although the etiology of ulcerative colitis (UC) differs from that of Crohn's disease, randomized controlled trials have demonstrated that infliximab is also beneficial for the treatment of moderate to severe UC in patients who are either intolerant of or refractory to immunosuppressant agents or steroids, or those who are steroid-dependent. A review of the literature is followed by practical recommendations regarding infliximab that address the needs of clinicians and UC patients. Where there is a lack of evidence-based information, the expert panel provides its combined opinion derived from the members' clinical experiences.

Impaired mucosal defense to acute colonic injury in mice lacking cyclooxygenase-1 or cyclooxygenase-2.

To investigate roles in intestinal inflammation for the 2 cyclooxygenase (COX) isoforms, we determined susceptibility to spontaneous and induced acute colitis in mice lacking either the COX-1 or COX-2 isoform. We treated wild-type, COX-1(-/-), COX-2(-/-), and heterozygous mice with dextran sodium sulfate (DSS) to provoke acute colonic inflammation, and we quantified tissue damage, prostaglandin (PG) E(2), and interleukin-1beta. No spontaneous gastrointestinal inflammation was detected in mice homozygous for either mutation, despite almost undetectable basal intestinal PGE(2) production in COX-1(-/-) mice. Both COX-1(-/-) and COX-2(-/-) mice showed increased susceptibility to a low-dose of DSS that caused mild colonic epithelial injury in wild-type mice. COX-2(-/-) mice were more susceptible than COX-1(-/-) mice, and selective pharmacologic blockade of COX-2 potentiated injury in COX-1(-/-) mice. At a high dose, DSS treatment was fatal to 50% of the animals in each mutant group, but all wild-type mice survived. DSS treatment increased PGE(2) intestinal secretion in all groups except COX-2(-/-) mice. These results demonstrate that COX-1 and COX-2 share a crucial role in the defense of the intestinal mucosa (with inducible COX-2 being perhaps more active during inflammation) and that neither isoform is essential in maintaining mucosal homeostasis in the absence of injurious stimuli.

Clinical, endoscopic and radiographic outcomes with ustekinumab in medically-refractory Crohn's disease: real world experience from a multicentre cohort.

BACKGROUND: Ustekinumab is a monoclonal antibody targeting interleukins-12 and -23, with efficacy in Crohn's disease (CD) demonstrated in clinical trials. AIM: To assess the real-world clinical, endoscopic and radiographic response and remission outcomes achieved with ustekinumab in medically-refractory CD. METHODS: A retrospective multicentre cohort study was performed on CD patients receiving ustekinumab between 2011 and 2016. The primary outcome was achievement of clinical and objective steroid-free response and remission at 3, 6 and 12 months. Clinical response and remission were defined by reduction in Harvey Bradshaw Index (HBI) of ≥3 points and an HBI ≤4 points respectively. Objective response was defined by improvement in endoscopic or radiographic CD, as assessed by ileocolonoscopy, contrast-enhanced ultrasound or CT/MR enterography. Objective remission was defined by endoscopic mucosal healing or complete resolution of inflammatory parameters on radiographic assessment. RESULTS: A total of 167 CD patients were treated with ustekinumab. 95.2% (159/167) previously failed anti-TNF therapy. Median follow-up was 45.6 weeks (IQR: 24.4-88.9). At 3 months, clinical response was achieved in 38.9% (65/167) and remission in 15.0% (25/167) of patients. At 6 months, clinical response was achieved in 60.3% (91/151) and remission in 25.2% (38/151) of patients. At 12 months, clinical response was achieved in 59.5% (66/111) and remission in 27.9% (31/111) of patients. Endoscopic or radiographic response was demonstrated in 54.5% (67/123) at 6 months and 55.8% (48/86) of patients at 12 months. CONCLUSIONS: Ustekinumab is an effective therapeutic option for inducing and maintaining clinical, endoscopic and radiographic response in patients with Crohn's disease failing anti-TNF therapy.

The effect of immunosuppressive agents on monocyte generation and cytokine expression.

SUMMARY: : The purpose of this study was to determine the effect of immunosuppressive drugs on the production of inflammatory cytokines and on the generation of macrophages from bone marrow precursors. Lipopolysaccharide-stimulated peripheral blood mononuclear cells (PBMCs) were cultured in the presence of therapeutic concentrations of 6-mercaptopurine (6-MP), methotrexate (MTX), or prednisolone. The effect of these drugs on the expression of interleukin (IL)-lß, IL-8, and tumor necrosis factor-α (TNF-α) was studied using bioassays and Northern analysis. The generation of monocytes/macrophages from precursors in the bone marrow was examined by culturing murine bone marrow cells with macrophage colony-stimulating factor (M-CSF) in the presence or absence of these agents. 6-MP and MTX did not inhibit the production or messenger RNA (mRNA) expression of the macrophage-derived cytokines, although prednisolone did. Both 6-MP and MTX substantially decreased the generation of macrophages from bone marrow precursors. We conclude that the beneficial effects of these immunosuppressive agents might be due to the suppression of the generation of monocytes in the bone marrow precursors, secondarily diminishing the production of cytokines, eicosanoids, and the production of free radicals.

Role of animal models for the pathogenesis and treatment of inflammatory bowel disease.

The etiology of chronic inflammatory bowel diseases (IBD) such as Crohn's disease and ulcerative colitis is still unknown. Recent studies including animal models of intestinal inflammation have identified interactions between the mucosal immune system, host genetic susceptibility and environmental factors, including normal intestinal microflora. Although the ideal animal model of IBD has not been found, each model can study pathogenetic factors such as acute intestinal injury and healing, acute and chronic inflammation, regulation by key cytokines, T-lymphocyte mediation, the role of luminal bacteria, immunoregulatory factors and genetic susceptibility. The relevance of these studies for the treatment of IBD is also discussed.

Adalimumab dose escalation is effective for managing secondary loss of response in Crohn's disease.

BACKGROUND: The efficacy of adalimumab in maintaining remission in Crohn's disease patients may wane over time, leading to secondary loss of response that is often managed with dose escalation. However, the response to adalimumab dose escalation and long-term outcomes after escalation have not been well evaluated. AIMS: To characterise the short- and long-term clinical responses to adalimumab dose escalation for secondary loss of response. METHODS: A retrospective cohort study evaluating Crohn's disease out-patients requiring adalimumab dose escalation for secondary loss of response from 2003 to 2013 was conducted. The primary outcome was the proportion of patients achieving symptomatic clinical response to dose escalation and subsequent development of tertiary loss of response. Duration of regained response was assessed by Kaplan-Meier analysis. RESULTS: Ninety-two CD patients met inclusion criteria with mean duration of follow-up of 170.2 weeks (±129.6 weeks). Disease distribution was predominantly ileal (37/92, 40.2%) or ileocolonic (43/92, 46.7%), with equal distribution of inflammatory (34.8%), stricturing (27.2%), and penetrating (38.0%) disease phenotypes. At 24 weeks post-dose escalation, 74/92 (80.4%) patients had symptomatic clinical response. Among responders, median duration of sustained response was 69.2 weeks (IQR 29.4-107.1) but 42/74 (56.8%) responders experienced subsequent tertiary loss of response at a median time of 47.9 weeks (IQR 24.7-80.3). C-reactive protein >10.0 mg/L at the time of dose escalation predicted tertiary loss of response in univariate analysis (OR 3.32, 95% CI: 1.18-9.37). CONCLUSIONS: In patients with Crohn's disease, adalimumab dose escalation is effective for recapturing symptomatic response after secondary loss of response, but more than half will eventually experience a tertiary loss of response.

Systematic review: faecal transplantation for the treatment of Clostridium difficile-associated disease.

BACKGROUND: Management of recurrent Clostridium difficile-associated disease (CDAD), particularly in elderly patients, remains clinically challenging. Faecal transplantation (FT) may restore normal microbiota and break the cycle of recurrent CDAD. AIM: To critically appraise the clinical research evidence on the safety and effectiveness of FT compared with standard care in the treatment of patients with CDAD. METHODS: A comprehensive literature search was conducted by a research librarian to identify relevant studies published between 2000 and 2011. The Cochrane Library, PubMed, EMBASE, CINAHL, Biological Abstracts, BIOSIS Previews and Web of Science were searched using the following Medical Subject Headings (MeSH) terms and keywords, alone or in combination: Clostridium infections/Clostridium difficile/pseudomembranous/colitis/faeces/rectal/colon flora/gastrointestinal/nasogastric tube/enema/donor/transplant/infusion/bacteriotherapy/human probiotic infusion. Methodological quality of the included case series studies was assessed in terms of patient selection criteria, consecutive recruitment, prospective data collection, reporting of lost to follow-up, and follow-up rates. RESULTS: No controlled studies were found. Based on the weak evidence from seven full-text case series studies of 124 patients with recurrent/refractory CDAD, FT appears to be a safe and effective procedure. In most cases (83%) symptoms improved immediately after the first FT procedure, and some patients stayed diarrhoea free for several months or years. CONCLUSIONS: Although these results appear to be promising, the treatment effects of faecal transplantation cannot be determined definitively in the absence of a control group. Results from randomised controlled trials that compare faecal transplantation to oral vancomycin without or with a taper regimen will help to better define the role of faecal transplantation in the management of recurrent CDAD.

Adoptive transfer of nontransgenic mesenteric lymph node cells induces colitis in athymic HLA-B27 transgenic nude rats.

HLA-B27 transgenic (TG) rats develop spontaneous colitis when colonized with intestinal bacteria, whereas athymic nude (rnu/rnu) HLA-B27 TG rats remain disease free. The present study was designed to determine whether or not HLA-B27 expression on T cells is required for development of colitis after transfer of mesenteric lymph node (MLN) cells into rnu/rnu HLA-B27 recipients. Athymic nontransgenic (non-TG) and HLA-B27 TG recipients received MLN cells from either TG or non-TG rnu/+ heterozygous donor rats that contain T cells. HLA-B27 TG rnu/rnu recipients receiving either non-TG or TG MLN cells developed severe colitis and had higher caecal MPO and IL-1beta levels, and their MLN cells produced more IFN-gamma and less IL-10 after in vitro stimulation with caecal bacterial lysate compared to rnu/rnu non-TG recipients that remained disease free after receiving either TG or non-TG cells. Interestingly, proliferating donor TG T cells were detectable one week after adoptive transfer into rnu/rnu TG recipients but not after transfer into non-TG recipients. T cells from either non-TG or TG donors induce colitis in rnu/rnu TG but not in non-TG rats, suggesting that activation of effector T cells by other cell types that express HLA-B27 is pivotal for the pathogenesis of colitis in this model.

Nutritional issues in inflammatory bowel disease.

Malnutrition is a very common problem in patients with chronic inflammatory bowel diseases. This article discusses the incidence, causes, and clinical consequences of malnutrition in these patient groups. The role of nutritional support administered enterally or parenterally either as primary or adjunctive therapy is highlighted, based on past and more recent controlled studies. Additional attention is given to the roles of glutamine, short-chain fatty acids, fish oil, and alternative nutritional therapy.

A critical value for O2 transport in the rat.

Rat skeletal muscle O2 uptake (VO2) has been reported to be supply dependent even at normal blood flow rates. To find the point at which whole-animal VO2 became dependent on total O2 transport (TOT), intact anesthetized rats were ventilated under hypoxic, normoxic, and hyperoxic conditions while either normovolemic or hypovolemic. In this manner, TOT (cardiac output X arterial O2 content) was varied over a range of 5-80 ml . kg-1 . min-1 . VO2 was measured in a closed-circuit, double servospirometer system. O2 contents were measured in carotid artery and right heart blood. Arterial PCO2, pH, and rectal temperature were kept within normal limits. Above a TOT of 23 ml . kg-1 . min-1, reciprocal changes in O2 extraction and cardiac output maintained VO2 independently of TOT (VO2 = 17.9 +/- 1.3 ml . kg-1 . min-1). Below a TOT of 23 ml . kg-1 . min-1, Vo2 became linearly dependent upon TOT. For TOT between 5 and 16 ml . kg-1 . min-1, VO2 = 0.89 + 0.78 TOT (r = 0.98). These data indicate that above a critical TOT of approximately 23 ml . kg-1 . min-1, VO2 in anesthetized rats does not depend on TOT.

Inhibition of murine T cell activation by cholera toxin B subunit is not mediated through the phosphatidylinositol second messenger system.

Although cholera toxin B subunit is a potent mucosal immunogen in vivo, its predominant effect in vitro is inhibition of T cell and B cell activation. We reported earlier that this inhibition was not mediated through activation of adenylate cyclase and increases in intracellular cAMP. There is increasing evidence that T cell activation is initiated through the phosphatidyl inositol second messenger system in which phosphatidyl inositol bisphosphate is hydrolyzed by phospholipase C, producing inositol trisphosphate (IP3) and diacylglycerol. IP3 increases cytosolic calcium and diacylglycerol binds, translocates, and activates protein kinase C (PKC). These signals lead to a complex series of events eventuating in activation of a number of genes important in cell proliferation. In this study, we asked whether the mechanism of T cell inhibition by B subunit of cholera toxin (CT-B) was due to interference with the phosphatidyl inositol second messenger system. We found that substitution of ionomycin and PMA for IP3 and diacylglycerol, respectively, in culture induced T cell proliferation but only if both were present simultaneously. Such proliferation was inhibited by CT-B even if added hours after the start of culture. An assay for cytosolic PKC activity demonstrated that PMA translocation of PKC from cytosol to membrane was not inhibited by CT-B, indicating that CT-B does not inhibit activation of PKC. There was no inhibition of Con A-stimulated T cell phosphoinositol turnover. Moreover, Con A added to Fura-2 AM-loaded cells caused a rapid rise in cytosolic calcium, which CT-B preincubation did not alter. These results indicate that CT-B did not inhibit IP3 generation or action. We next looked at expression of genes involved in T cell proliferation. CT-B inhibited the production of IL-2 by mitogen-activated T cells; Northern analysis showed that this inhibition was associated with decreased levels of IL-2 mRNA. Expression of IL-2R and of transferrin receptors was only modestly reduced. Despite the presence of IL-2R on the T cells exposed to CT-B, the addition of exogenous IL-2 to the cultures did not reverse the CT-B-induced T cell inhibition. We conclude that the T cell inhibition by CT-B is not mediated by interference with the activation of the phosphatidylinositol second messenger system but occurs at a later stage of T cell activation.

Kinetics of cytokine expression during healing of acute colitis in mice.

The mechanisms of wound healing in the gut are poorly understood but are mediated by cytokines in other tissues. In this study we wanted to determine which cytokines were expressed after nonspecific colonic injury, the kinetics of that expression, and how cytokine expression correlated with tissue histology. At 0, 4, 8, 12, 24, 48, and 72 h after intrarectal administration of 3% acetic acid to C3H/HeJ mice, their colons were removed for histology, organ culture, and RNA extraction. Cytokine mRNA expression for various cytokines was assessed by reverse transcriptase-polymerase chain reaction with primers specific for each cytokine. Cytokine production in organ cultures was measured with bioassays. Shortly after colonic injury and during colonic regeneration, proinflammatory cytokines such as interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein (MIP), and transforming growth factor-beta (TGF-beta) were expressed. In contrast, expression of T cell-derived cytokines was not detected at any time point. Cytokines such as IL-1 beta, IL-6, IL-10, TNF-alpha, and MIP-1 are important mediators of tissue repair and restitution after nonspecific colonic injury and may subserve a similar role in human colitis.

Dextran sulfate sodium-induced colitis occurs in severe combined immunodeficient mice.

BACKGROUND/AIMS: Oral administration of dextran sulfate sodium (DSS) has been reported to induce colitis in mice. The purpose of this study was to determine whether the possible pathogenic mechanism involved the acquired immune system. METHODS: Normal BALB/c and related C.B17 severe combined immunodeficient mice were fed 5% DSS (40 kilodaltons) in their drinking water for 7 days; controls were fed only water. Colons were scored for histological activity at various times. Cytokine production by cultures of colon and of draining lymph node cell was measured. The effect of DSS on the proliferation of the MCA-38 colonic epithelial cell line was assessed. RESULTS: DSS feeding resulted in a very reproducible acute distal colitis in both BALB/c and C.B17 severe combined immunodeficient mice. The lesions of BALB/c mice had an increased production of macrophage-derived cytokines, such as interleukin (IL) 1 beta, IL-6, tumor necrosis factor, and granulocyte-macrophage colony-stimulating factor, but not the T-cell cytokines IL-3 or interferon gamma. Draining lymph node cells produced these cytokines plus interferon gamma and IL-3. DSS inhibited MCA-38 cells at doses that would be easily achieved in the distal colon. CONCLUSIONS: Acute DSS-induced colitis does not require the presence of T cells or B cells because it occurred in C.B17 severe combined immunodeficient mice that lack these cells. Its induction may result from a toxicity of DSS for colonic epithelial cells.

Effects of local budesonide treatment on the cell-mediated immune response in acute and relapsing colitis in rats.

Glucocorticosteroids (GCS) are effective in treatment of inflammatory bowel disease (IBD), but also have unwanted systemic side effects. Here, we describe the effects of budesonide and dexamethasone on acute experimental colitis and on T cells in thymus and spleen, as well as the effect of budesonide treatment on relapsing colitis. Acute colitis was induced by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in ethanol, and a relapse was induced by an intraperitoneal booster of TNBS. GCS were administered intrarectally on days 1, 4, and 6 after induction of acute colitis or a relapse. Inflammatory cells in the colon were studied on day 7, and in acute colitis also on days 13 and 16. Budesonide treatment in acute and relapsing colitis resulted in reduction of macroscopic damage and decreased the numbers of macrophages and neutrophils in the colon. Dexamethasone was less effective. Dexamethasone, but not budesonide, reduced the number of T cells in the thymus. It is concluded that local budesonide is more effective in treatment of acute experimental colitis than dexamethasone and, in contrast to dexamethasone, did not cause a general suppression of T cells. Although budesonide was very effective in the treatment of relapsing colitis, this effect was not accomplished by affecting the number of T cells in the colon.

Leukocyte migration in experimental inflammatory bowel disease.

Emigration of leukocytes from the circulation into tissue by transendothelial migration, is mediated subsequently by adhesion molecules such as selectins, chemokines and integrins. This multistep paradigm, with multiple molecular choices at each step, provides a diversity in signals. The influx of neutrophils, monocytes and lymphocytes into inflamed tissue is important in the pathogenesis of chronic inflammatory bowel disease. The importance of each of these groups of adhesion molecules in chronic inflammatory bowel disease, either in human disease or in animal models, will be discussed below. Furthermore, the possibilities of blocking these different steps in the process of leukocyte extravasation in an attempt to prevent further tissue damage, will be taken into account.

Acquired Zwa antigen on Zwa negative platelets demonstrated by western blotting.

Zwa-negative platelets that had been incubated in random donor AB plasma for several hours and subsequently cryopreserved, were found to be Zwa-positive when tested 3 years later by Western blotting. Following this serendipitous observation, we demonstrated that the Zwa antigen could be passively adsorbed onto the membrane of Zwa-negative platelets incubating for 4 h in the plasma from Zwa-positive donors. This observation supports the hypothesis that passive acquirement of Zwa antigens is a pathogenic mechanism for inducing post-tranfusion purpura, and suggests that Zwa-negative platelets should not be stored in Zwa-positive plasma before transfusion.