PubMed Health⌕ Search

Biomedical subjects

Robert D Inman

Publications and source records attributed to Robert D Inman.

At least 37 records · Page 2Linked to original sources
PubMed2005

Innate immunity and arthritis: neutrophil Rac and toll-like receptor 4 expression define outcomes in infection-triggered arthritis.

OBJECTIVE: The role of innate immunity in Chlamydia-induced arthritis has not been defined. The purpose of this study was to examine the role of neutrophils in experimental arthritis in mice with targeted elimination of the small GTPases Rac1 and Rac2, as well as the role of Toll-like receptors (TLRs) in this model. METHODS: Arthritis was induced by intraarticular inoculation of synoviocyte-packaged Chlamydia trachomatis. The degree of arthritis was assessed according to joint swelling and pathology scores. The persistence of Chlamydia in joints was assessed by immunoassay. The expression of TLR-2 and TLR-4 in neutrophils was detected by semiquantitative reverse transcription-polymerase chain reaction. RESULTS: In the acute phase, wild-type mice developed more severe arthritis than did Rac-deficient mice, with abundant infiltration of neutrophils into the joint. In the chronic phase, the Rac-deficient mice developed more severe arthritis and demonstrated defective clearance of the pathogen from the joint. In vitro stimulation of neutrophils with Chlamydia up-regulated the expression of TLR-4, but not TLR-2, in wild-type mice. However, neutrophils from Rac-deficient mice did not show this up-regulation of TLR-4. Sustained TLR-4 expression in neutrophils was found to be dependent on the expression of Rac. Mice genetically deficient in TLR-4 demonstrated more severe arthritis than did the controls. Thus, Rac expression plays a profound role in infection-triggered arthritis and demonstrates a bimodal influence on the disease process, exacerbating acute joint inflammation but controlling chronic arthritis. Rac deficiency was associated with diminished TLR-4 expression, impaired host clearance of the pathogen, and more severe chronic arthritis. CONCLUSION: In infection-triggered arthritis, innate immunity plays a critical role. Effective host clearance of an arthritogenic pathogen depends on intact expression of Rac and appropriate expression of TLR-4 by neutrophils.

Animals↗
PubMed2005

Pathogenesis of ankylosing spondylitis and reactive arthritis.

PURPOSE OF REVIEW: The hallmark of ankylosing spondylitis is acute and chronic spinal inflammation initiating in the sacroiliac joints, often coupled with enthesitis, presenting as chronic inflammation at the sites of ligamentous and tendinous insertions into bone. Peripheral joint synovitis can be a prominent feature as well. Reactive arthritis is a sterile synovitis arising after an extra-articular infection of enteric or urogenital tracts. HLA-B27 has been known for about the past 30 years to be associated with ankylosing spondylitis and reactive arthritis, but the pathogenesis of ankylosing spondylitis and reactive arthritis is still not well defined. Although the clinical manifestations of ankylosing spondylitis and reactive arthritis may differ, this update discusses the two diseases together and focuses on recent evidence in both. RECENT FINDINGS: With respect to HLA-B27 several recent studies address arthritogenic peptides, molecular mimicry, and aberrant forms of B27. Several candidate genes in addition to B27 have been implicated in recent genetic studies. With respect to bacterial infection, recent findings in bacterial antigenicity, host response through interactions of antigen-presenting cells, T cells, and cytokines are providing new understanding of host-pathogen interactions and the pathogenesis of arthritis. Endogenous host factors such as proteoglycans may play a role as autoantigens and contribute to chronic inflammation on that basis. SUMMARY: Recent advances provide additional new insights into distinct pathogenetic mechanisms in AS and ReA that arise from a complex interplay between genetic factors including HLA-B27 and environmental factors.

Arthritis, Reactive↗
PubMed2005

Baseline factors that influence ASAS 20 response in patients with ankylosing spondylitis treated with etanercept.

OBJECTIVE: To examine the baseline demographic and disease characteristics that might influence improvement as measured by the Assessment in Ankylosing Spondylitis Response Criteria (ASAS 20) in patients with ankylosing spondylitis (AS). METHODS: A multicenter Phase 3 study was performed to compare the safety and efficacy of 24 weeks of etanercept 25 mg subcutaneous injection twice weekly (n = 138) and placebo (n = 139) in patients with AS. The ASAS 20 was measured at multiple time points. Using a significance level of 0.05, a repeated measures logistic regression model was used to determine which baseline factors influenced response in the etanercept-treated patients during the 24-week double blind portion of the trial. The following baseline factors were used in the model: demographic and disease severity variables, concomitant medications, extra-articular manifestations, and HLA-B27 status. The predictive capability of the model was then tested on the patients receiving placebo after they had received open-label etanercept treatment. RESULTS: Baseline factors that were significant predictors of an ASAS 20 response in etanercept-treated patients were C-reactive protein (CRP), back pain score, and Bath Ankylosing Spondylitis Functional Index (BASFI) score. Although clinical response to etanercept was seen at all levels of baseline disease activity, responses were consistently more likely with higher CRP levels or back pain scores and less likely with increased BASFI scores at baseline. CONCLUSIONS: Higher CRP values and back pain scores and lower BASFI scores at baseline were significant predictors of a higher ASAS 20 response in patients with AS receiving etanercept but predictive value was of insufficient magnitude to determine treatment in individual patients.

Adult↗
PubMed2005

Interleukin 1 and nuclear factor-kappaB polymorphisms in ankylosing spondylitis in Canada and Korea.

OBJECTIVE: The interleukin 1alpha and 1beta (IL-1alpha, IL-1beta) are potent mediators of inflammation and immunity. IL-1 receptor antagonist (IL-1Ra) is a protein that binds to IL-1 receptors and competitively inhibits the binding of IL-1alpha and IL-1beta. There are reports of IL-1 complex gene polymorphisms in ankylosing spondylitis (AS), but the results have been inconsistent. NFKB1 encodes the genes for the p50 and p101 nuclear factor-kappaB (NF-kappaB) isoforms, which are recognized as critical to inflammatory disease. To date there have been no reports examining an association between NFKB1 and AS. We investigated polymorphisms of IL-1 complex and NF-kappaB1 with 2 genetically and geographically different populations. METHODS: Subjects with AS satisfied modified New York criteria for AS. Healthy controls were recruited at each respective site. Subjects with AS were genotyped for the following: IL-1alpha-889 single nucleotide polymorphism (SNP); IL-1beta +3953 SNP; IL-1Ra (86 base pair variable number tandem repeat within intron 2); and NFKB1 (-94 insertion/deletion polymorphism). RESULTS: In total, 205 subjects with AS and 200 controls from Seoul, Korea, and 68 subjects with AS and 164 controls from Toronto, Canada, were genotyped for the IL-1alpha and IL-1beta polymorphisms and 115 controls for the IL-1Ra and NF-kappaB polymorphisms. There were no differences of IL-1alpha, IL-1beta, IL-1Ra, and NF-kappaB polymorphisms between AS patients and controls in these populations. CONCLUSION: Our analysis of these SNP in the IL-1 complex and NF-kappaB genes does not support a major role for either in AS susceptibility in the Seoul and Toronto populations.

Adult↗
PubMed2004

Validation exercise of the Ankylosing Spondylitis Assessment Study (ASAS) group response criteria in ankylosing spondylitis patients treated with biologics.

OBJECTIVES: To define what expert clinicians consider a dramatic response in ankylosing spondylitis (AS) patients treated with biologic therapies based on patient and physician assessments of global disease activity. To compare this expert clinician-derived criteria to the Ankylosing Spondylitis Assessment Study (ASAS) Group criteria for improvement. METHODS: Forty consecutive AS patients were treated in a 1-year open-label protocol with infliximab. Response to treatment at week 52 was defined using ASAS response criteria. For the purpose of this exercise, improvement using ASAS criteria was defined by consensus among experts as good with 50% improvement from baseline (ASAS(50)) and dramatic with 70% improvement from baseline (ASAS(70)). Experts established separate criteria for improvement in disease activity as good or dramatic based on patient and physician global assessment of disease activity. RESULTS: Twelve of 40 patients met the ASAS(70) criteria, however, only 8 met the expert definition of a dramatic improvement based on physician global scores and 5 met the expert definition of a dramatic improvement based on patient global assessment of disease activity. Agreement was poor between ASAS(50) or ASAS(70) and expert definition of improvement based on physician global scores (kappa < 0.3), but agreement was moderate to good between ASAS(50) or ASAS(70) and expert definition of improvement based on patient global scores, (kappa = 0.6-0.7). CONCLUSIONS: Differential response experienced by AS patients treated with infliximab was adequately captured by the ASAS composite improvement criteria. Overall, this study demonstrates the validity of the ASAS criteria for the detection of improvement in AS patients treated with biologics. However, the patient global assessment of disease activity may be sufficient to monitor changes in disease activity in these patients.

Adult↗
PubMed2004

Genetic studies in familial ankylosing spondylitis susceptibility.

OBJECTIVE: To define the genetic basis of susceptibility to ankylosing spondylitis (AS), especially non-major histocompatibility complex (MHC) genes. METHODS: The study group comprised 244 affected sibling pairs from 180 pedigrees of primarily European ancestry. Sibling pairs were concordant for AS by the modified New York criteria and had available sacroiliac radiographs. The subjects were genotyped for 400 markers in ABI PRISM linkage map MD-10 and for 17 additional markers on chromosomes 6p, 6q, and 11q (including HLA-B, DRB1, DQA1, DQB1, and DPB1 alleles). Two-point and multipoint nonparametric linkage (NPL) analyses were conducted using the NPL statistic and 1-parameter allele-sharing model logarithm of odds (LOD) scores, calculated using the Allele-Sharing Model (ASM) computer program. RESULTS: Linkage of the MHC region was supported by both 2-point and multipoint analyses, with the strongest peak (45.90 cM) in the MHC at the HLA-DRB1 locus (NPL score 8.720, ASM LOD score 20.49; P = 6.8 x 10(-20) for 2-point analysis). A second region was found to have positive linkage at the q arm of chromosome 6 (D6S441) in 2-point analysis; this was supported by a 39.13-cM region (135.58-174.71 cM) in multipoint analysis, with the smallest P value (4.2 x 10(-3)) at 166.39 cM. A third region was found on chromosome 11q, with the strongest evidence for linkage for D11S4094 at 123 cM (NPL score 2.235, ASM LOD score 1.939) and, on transmission disequilibrium test analysis, D11S4090 at 105.74 cM (P = 6.2 x 10(-5)). Linkage in this area was supported by multipoint analysis, spanning 22.19 cM continuously from 101.68 cM to 123.87 cM, with the strongest peak at 112.33 cM (P = 0.014); this was confirmed by subsequent fine mapping studies. CONCLUSION: Thus, this genome-wide scan implicates, in addition to the MHC, regions outside the MHC in AS susceptibility, especially on chromosomes 6q and 11q.

Chromosome Mapping↗
PubMed2004

Synovial fibroblasts infected with Salmonella enterica serovar Typhimurium mediate osteoclast differentiation and activation.

The mechanisms whereby arthritogenic organisms may induce cartilage and bone erosions in infection-triggered arthritis remain unknown. In this study, we asked whether an arthritogenic organism could contribute to osteoclast differentiation and activation through regulation of the receptor activator of NF-kappaB ligand (RANKL) in synovial fibroblasts. Rat synovial fibroblasts were infected in vitro with Salmonella enterica serovar Typhimurium and monitored over time. The expression of RANKL in resting and infected synovial fibroblasts was quantified by reverse transcription-PCR and Western blotting. Osteoclast progenitors, isolated from femurs of 8-week-old rats and cultured in the presence of macrophage colony-stimulating factor, were cocultured with either infected or noninfected synovial fibroblasts for 2 to 4 days. Differentiation and maturation of osteoclasts were determined by morphology and tartrate-resistant acid phosphatase (TRAP) staining and by a bone resorption bioassay. RANKL expression was undetectable in resting synovial fibroblasts but was dose-dependently upregulated in cells after Salmonella infection. Osteoprotegerin was constitutively expressed by synovial fibroblasts and was not upregulated by infection. Further, we observed the formation of multinucleated TRAP-positive cells and formation of bone resorption pits in cocultures of bone marrow-derived osteoclast precursors with synovial fibroblasts infected with Salmonella but not with heat-killed Salmonella or noninfected cells. Arthritogenic bacteria may alter bone structure via synovial fibroblast intermediaries, since infected synovial fibroblasts (i) upregulate RANKL expression and (ii) enhance osteoclast precursor maturation into multinucleated, TRAP-positive, bone-resorbing, osteoclast-like cells. These data provide a link between infection and osteoclastogenesis. A better understanding of infection-mediated osteoclast differentiation and activation may provide new therapeutic strategies for inflammatory joint disease.

Animals↗
PubMed2004

Analysis of CARD15 polymorphisms in Korean patients with ankylosing spondylitis reveals absence of common variants seen in western populations.

OBJECTIVE: Substantial epidemiological and genetic evidence suggests that ankylosing spondylitis (AS) is likely due to an interplay of genetic and environmental factors. Recently, CARD15, located in chromosome 16q12, has been established as a disease susceptibility gene for Crohn's disease, Blau syndrome, and possibly psoriatic arthritis. Association studies in admixed populations from Northern European ancestry noted no such association between CARD15 mutations and AS. However, a homogenous population has yet to be studied. We investigated the prevalence of the 3 common CARD15 variants in a homogenous Korean population with AS. METHODS: All subjects were native Koreans with AS satisfying the modified New York criteria. Korean controls were examined and confirmed to be unaffected by AS. Subjects with AS were genotyped for the R702W, G908R, and Leu1007fsinsC variants of CARD15 using mass array MALDI-TOF mass spectrometry. RESULTS: A total of 205 AS subjects and 200 controls were genotyped. No subject with AS had any variants at the 702 and 1007 sites of CARD15. Only one subject was heterozygous for the 908 variant. The overall genotype frequency in AS for any CARD15 variant was 0.5%. No control had any of the 3 CARD15 variants. CONCLUSION: Our findings indicate that the CARD15 gene is not a major contributor to AS susceptibility in the Korean population.

Adult↗
PubMed2004

Common aspects of human and primate seronegative arthritis.

A 27-year-old female lowland gorilla developed an asymmetric oligoarthritis 3 months post-partum. There was no evidence of an antecedent gastrointestinal or genitourinary infection. Serum was negative for rheumatoid factor and antinuclear antibody. Synovial fluid revealed 2000 white blood cells with negative cultures and polarized microscopy. Studies on synoviocytes were the following: (1) FACS analysis revealed surface expression of a B27-like epitope of the cells. (2) Analysis of intracellular clearance kinetics of arthritogenic organisms showed peak intracellular colony-forming units at 48 hours after bacterial invasion, and clearance by 13 days post-invasion. (3) Interferon-y (0.1-10.0 ng/ml)accelerated intracellular microbicidal pathways in a dose-dependent fashion. These findings closely parallel those seen in human synoviocytes of patients with spondyloarthropathy. Primate and human seronegative arthritis share clinical and immunologic features, as well as aspects of host:pathogen defense mechanisms. The interplay of genetic and microbial factors underlying this arthritis appears to be conserved across these species boundaries.

Animals↗
PubMed2003

Novel genetic markers in the 5'-flanking region of ANKH are associated with ankylosing spondylitis.

OBJECTIVE: To use a candidate gene approach for the identification of genetic markers that are significantly linked to and associated with ankylosing spondylitis (AS). METHODS: We searched for novel polymorphisms in the ANKH gene (human homolog of the murine progressive ankylosis gene) and genotyped 2 polymorphic sites, one in the 5'-noncoding region and the other in the promoter region of ANKH, using DNA from affected (n = 273) and unaffected (n = 112) individuals from 124 AS families. We used these ANKH and other nearby polymorphisms to perform linkage and family-based association analyses. RESULTS: We identified 2 novel polymorphic sites: one in the 5'-noncoding region of ANKH involving 1-2 copies of an 8-bp repeat (denoted as ANKH-OR), and the other in the promoter region involving different copy numbers of a triplet repeat (denoted as ANKH-TR). ANKH-OR and ANKH-TR were in complete linkage disequilibrium. Five markers (D5S1953, ANKH-TR, ANKH-OR, D5S1954, and D5S1963) were used for both the linkage and association analyses. Multipoint linkage analysis of 124 AS families showed a modest level of significance (nonparametric linkage score 2.15; P = 0.015) at the ANKH region. The contribution of ANKH to AS susceptibility (lambda(s)) was 1.9. A family-based association study on the same AS families revealed that both ANKH-OR allele 1 and ANKH-TR allele 7 were significantly associated with disease, assuming an additive model (for ANKH-OR allele 1, P = 0.03; for ANKH-TR allele 7, P = 0.04). CONCLUSION: Our results indicate that ANKH-OR and ANKH-TR are novel genetic markers that are significantly associated with AS.

5' Flanking Region↗
PubMed2003

Molecular and cellular biology of new bone formation: insights into the ankylosis of ankylosing spondylitis.

One of the most distinctive features of the spondyloarthropathies is the tendency for new bone formation at sites of chronic inflammation. This is important diagnostically because radiographic evidence of ankylosis is often stated as one of the classification criteria, and it is important clinically because loss of spinal mobility over time is a major contributor to disability in this disease. The mechanisms underlying this tendency for ankylosis have not yet been defined. This review updates current concepts of the molecular and cellular basis of normal and abnormal bone formation. A better understanding of this process may open new avenues of therapeutic intervention in these chronic diseases.

Cell Lineage↗
PubMed2003

Determinants of synoviocyte clearance of arthritogenic bacteria.

OBJECTIVE: Persistence of intracellular organisms may play a critical role in the initiation and perpetuation of synovitis in reactive arthritis (ReA). We investigated factors that may influence local clearance of arthritogenic pathogens in ReA. METHODS: We studied 11 HLA-B27 positive patients with spondyloarthropathies and contrasted these patients with 6 HLA-B27 negative control patients with rheumatoid arthritis or osteoarthritis. We employed an ex vivo system in which human synoviocytes derived from patients with ReA are cocultured with arthritogenic pathogens, and intracellular clearance is measured by quantitating colony-forming units over time. RESULTS: The clearance kinetics of the organisms bore no relationship to the HLA-B27 status of the patient. Clearance of S. typhimurium over a 10 day period was accompanied by a progressive rise in nitric oxide (NO) production, but this appeared not to be rate-limiting, since (1) clearance kinetics were comparable between high versus low NO-producing synoviocytes; and (2) L-NMMA inhibition of NO production did not alter clearance kinetics of S. typhimurium. Interferon-g (IFN-g) was observed to have a small but measurable effect on bacterial clearance. In certain patients with ReA there was a paradoxical stimulatory response to IFN-g, in which the addition of IFN-g was accompanied by an increase in intracellular bacteria. This effect was found to be attributable to IFN-g mediated suppression of NO production in these cells. This pattern was not observed in B27 negative synoviocytes. CONCLUSION: Intracellular persistence of arthritogenic organisms may contribute to the cellular basis of ReA, but the molecular basis of the bacteriocidal pathways in synoviocytes has not been fully resolved. Our findings indicate that a direct effect of HLA-B27 on these events is unlikely, but that alterations in cytokine response profiles may play a contributory role. Characterizing these mechanisms holds the promise of more specific therapeutic interventions in this disease.

Adult↗
PubMed2003

Canadian Rheumatology Association Consensus on the use of anti-tumor necrosis factor-alpha directed therapies in the treatment of spondyloarthritis.

Spondyloarthritis (SpA) represents a group of related arthritides characterized by their association with HLA-B27 and the development of sacroiliitis and enthesitis. Functional impairment, disability, and loss of quality of life may resemble that observed in rheumatoid arthritis. The SpA Research Consortium of Canada (SPARCC) is an informal association of rheumatologist members of the Canadian Rheumatology Association (CRA) with a special interest in therapeutics and outcomes research in SpA. Recent experience with anti-tumor necrosis factor-a (anti-TNF-a) directed therapies prompted a consensus-based evaluation of the evidence supporting their efficacy, safety, and appropriate use in SpA. We evaluated the clinical evidence in support of anti-TNF-a directed therapies in SpA. Medline was searched using appropriate keywords. Abstracts of the 1999-2002 annual meetings of the American College of Rheumatology and the European Congress of Rheumatology were extracted and admitted if sufficient detail was available to determine the level of evidence. Recommendations were based on randomized placebo-controlled trials (Level A evidence) and clinical studies without randomization (Level B evidence). Where the scientific literature was incomplete, recommendations reflected the consensus of SPARCC members (Level C evidence). Following development of an original draft document, consensus for revisions was achieved among members of SPARCC. The document was then posted on the CRA website prior to its final revision. The following recommendations have been endorsed by the Therapeutics Committee of the CRA: Infliximab and etanercept are indicated for reduction of signs and symptoms of moderate to severely active SpA in patients who have had an inadequate response to maximal doses of > or = 2 nonsteroidal antiinflammatory drugs (NSAID) over a 3-month period of observation; and either sulfasalazine or methotrexate is indicated in those with predominantly active peripheral arthritis. Current evidence supports their use as monotherapy (level of evidence A) for at least one year. NSAID and/or second line therapy with either sulfasalazine or methotrexate can be continued concomitantly. There is no evidence addressing potential advantages or disadvantages of combining methotrexate with anti-TNF therapy for SpA. Recommended doses for adults are: infliximab 5 mg/kg at 0, 2, and 6 weeks and every 8 weeks thereafter; etanercept 25 mg subcutaneously twice weekly. No therapy has been shown to slow progression of axial disease in SpA, and prognostic factors for determining response to therapy remain to be determined. It is the position of the CRA that all therapeutic options should be equally available according to the best judgments of the treating physician and the informed decision of the patient.

Antibodies, Monoclonal↗
PubMed2003

Should tetracycline treatment be used more extensively for rheumatoid arthritis? Metaanalysis demonstrates clinical benefit with reduction in disease activity.

OBJECTIVE: To compare the effectiveness of tetracycline antibiotics versus control (placebo or conventional treatment) in rheumatoid arthritis (RA) for the reduction of disease activity as defined by American College of Rheumatology criteria. METHODS: We searched Medline (1966-February 2002), Embase (1980-February 2002), and the Cochrane Controlled Trials Register (Issue 1, 2002 Cochrane Library). Reference lists of published trials were searched by hand for further identification of published reports and presentations at scientific meetings. Randomized controlled trials comparing tetracyclines to control (placebo or conventional disease modifying antirheumatic therapy) were selected for inclusion if at least one of the following outcomes was reported: tender joint count (TJC), swollen joint count, patient pain score by visual analog scale, patient global assessment of disease activity, physician global assessment of disease activity, eosinophil sedimentation rate (ESR) and C-reactive protein (CRP), joint space narrowing and erosions, adverse events, and quality of life as measured by the Health Assessment Questionnaire. Subjects were required to have RA as defined by the 1987 ARA criteria. RESULTS: Ten randomized controlled trials including 535 individuals were reviewed. Only 3 trials were considered high quality; elements of bias could not be excluded in the remainder. Tetracyclines, when administered for > or = 3 months, were associated with a significant reduction in disease activity in RA as follows: for TJC, standardized mean difference (SMD) = -0.39, 95% CI -0.74, -0.05; and for acute phase reactants, ESR, SMD = -8.96, 95% CI -14.51, -3.42. The treatment effect was more marked in the subgroup of patients with disease duration < 1 year who were seropositive. There was no absolute increased risk of adverse events associated with tetracyclines: absolute risk difference = 0.10, 95% confidence interval (CI) -0.01, 0.21. No beneficial effect was seen on radiological progression of disease: for erosions, SMD = 0.17, 95% CI -0.29, 0.64. In addition, subgroup analysis excluding trials with doxycycline showed that minocycline alone had a greater effect on reduction of disease activity: for TJC, SMD = -0.69, 95% CI -0.89, -0.49; and for ESR, SMD = -10.14, 95% CI -14.72, -5.57. CONCLUSION: Tetracyclines, in particular minocycline, were associated with a clinically significant improvement in disease activity in RA with no absolute increased risk of side effects. Unfortunately, the information available was inadequate to allow a detailed analysis of individual side effects in the studies. Further research is warranted to compare these agents to newer disease modifying drugs for comparable safety, efficacy, and cost-effectiveness.

Antirheumatic Agents↗
PubMed2002

Differential role of actin, clathrin, and dynamin in Fc gamma receptor-mediated endocytosis and phagocytosis.

Clustering of macrophage Fc gamma receptors by multimeric immunoglobulin complexes leads to their internalization. Formation of small aggregates leads to endocytosis, whereas large particulate complexes induce phagocytosis. In RAW-264.7 macrophages, Fc gamma receptor endocytosis was found to be dependent on clathrin and dynamin and insensitive to cytochalasin. Clathrin also associates with nascent phagosomes, and earlier observations suggested that it plays an essential role in phagosome formation. However, we find that phagocytosis of IgG-coated large (> or =3 microm) particles was unaffected by inhibition of dynamin or by reducing the expression of clathrin using antisense mRNA but was eliminated by cytochalasin, implying a distinct mechanism dependent on actin assembly. The uptake of smaller particles (< or =1 microm) was only partially blocked by cytochalasin. Remarkably, the cytochalasin-resistant component was also insensitive to dominant-negative dynamin I and to clathrin antisense mRNA, implying the existence of a third internalization mechanism, independent of actin, dynamin, and clathrin. The uptake of small particles occurred by a process distinct from fluid phase pinocytosis, because it was not inhibited by dominant-negative Rab5. The insensitivity of phagocytosis to dominant-negative dynamin I enabled us to test the role of dynamin in phagosomal maturation. Although internalization of receptors from the plasma membrane was virtually eliminated by the K44A and S45N mutants of dynamin I, clearance of transferrin receptors and of CD18 from maturing phagosomes was unaffected by these mutants. This implies that removal of receptors from the phagosomal membrane occurs by a mechanism that is different from the one mediating internalization of the same receptors at the plasma membrane. These results imply that, contrary to prevailing notions, normal dynamin and clathrin function is not required for phagocytosis and reveal the existence of a component of phagocytosis that is independent of actin and Rab5.

Actins↗