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Biomedical subjects

Enrique Freer

Publications and source records attributed to Enrique Freer.

6 recordsLinked to original sources
PubMed2006

Persistent human papillomavirus infection is associated with a generalized decrease in immune responsiveness in older women.

The development of cervical cancer and its precursors are linked to persistent infection with oncogenic types of human papillomavirus (HPV). Host immune responses seem to be determinants of risk for this disease. However, little is known about the immunologic determinants of HPV persistence. Here, we examined the association between lymphoproliferative responses to antigens/mitogens and persistent HPV infection in women older than 45 years. Women included in this study were participants in a 10,000-woman population-based cohort study of cervical neoplasia in Costa Rica. Women older than 45 years and HPV DNA positive at a screening visit were selected as cases (n = 283). We selected a comparably sized control group of HPV DNA-negative women, matched to cases on age and time since enrollment (n = 261). At an additional clinical visit, women were cytologically and virologically rescreened, and cervical and blood specimens were collected. Proliferative responses to phytohemagglutinin (PHA), influenza virus (Flu), and HPV16 virus-like particle (VLP) were lower among women with persistent HPV infection [median counts per minute (cpm): 72,849 for PHA, 1,241 for Flu, and 727 for VLP] than for the control group (median cpm: 107,049 for PHA, 2,111 for Flu, and 2,068 for VLP). The decreases were most profound in women with long-term persistence and were only observed for the oldest age group (>/=65 years). Our results indicate that an impairment in host immunologic responses is associated to persistent HPV infection. The fact that effects were evident for all studied stimuli is suggestive of a generalized effect.

Age Factors↗
PubMed2004

Adherence of Brucella to human epithelial cells and macrophages is mediated by sialic acid residues.

The basis for the interaction of Brucella species with the surface of epithelial cells before migration in the host within polymorphonuclear leucocytes is largely unknown. Here, we studied the ability of Brucella abortus and Brucella melitensis to adhere to cultured epithelial (HeLa and HEp-2) cells and THP-1-derived macrophages, and to bind extracellular matrix proteins (ECM). The brucellae adhered to epithelial cells forming localized bacterial microcolonies on the cell surface, and this process was inhibited significantly by pretreatment of epithelial cells with neuraminidase and sodium periodate and by preincubation of the bacteria with heparan sulphate and N-acetylneuraminic acid. Trypsinization of epithelial cells yielded increased adherence, suggesting unmasking of target sites on host cells. Notably, the brucellae also adhered to cultured THP-1 cells, and this event was greatly reduced upon removal of sialic acid residues from these cells with neuraminidase. B. abortus bound in a dose-dependent manner to immobilized fibronectin and vitronectin and, to a lesser extent, to chondroitin sulphate, collagen and laminin. In sum, our data strongly suggest that the adherence mechanism of brucellae to epithelial cells and macrophages is mediated by cellular receptors containing sialic acid and sulphated residues. The recognition of ECM (fibronectin and vitronectin) by the brucellae may represent a mechanism for spread within the host tissues. These are novel findings that offer new insights into understanding the interplay between Brucella and host cells.

Animals↗
PubMed2002

R-Ras glucosylation and transient RhoA activation determine the cytopathic effect produced by toxin B variants from toxin A-negative strains of Clostridium difficile.

Clostridium difficile induces antibiotic-associated diarrhea through the production of toxin A and toxin B; the former toxin has been assumed to be responsible for the symptoms of the disease. Several toxin A-negative strains from C. difficile have recently been isolated from clinical cases and have been reported to produce toxin B variants eliciting an atypical cytopathic effect. Ultrastructural analysis indicated these toxins induce a rounding cytopathic effect and filopodia-like structures. Toxin B variants glucosylated R-Ras, and transfection with a constitutively active mutant of this GTPase protected cells against their cytopathic effect. Treatment of cells with toxin B variants induced detachment from the extracellular matrix and blockade of the epidermal growth factor-mediated phosphorylation of extracellular-regulated protein kinases, demonstrating a deleterious effect on the R-Ras-controlled avidity of integrins. Treatment with toxin B variants also induced a transient activation of RhoA probably because of inactivation of Rac1. Altogether, these data indicate that the cytopathic effect induced by toxin B variants is because of cell rounding and detachment mediated by R-Ras glucosylation, and the induction of filopodia-like structures is mediated by RhoA activation. Implications for the pathophysiology of C. difficile-induced diarrhea are discussed.

3T3 Cells↗
PubMed2002

The flagella of enteropathogenic Escherichia coli mediate adherence to epithelial cells.

Enteropathogenic Escherichia coli (EPEC) utilizes a type III protein secretion system to target effector molecules into the host cell leading to effacement of the intestinal mucosa. This secretion apparatus shares many structural features of the flagellar type III export system involved in flagella assembly and motility. We report here that fliC insertional mutants constructed in two wild-type EPEC strains were markedly impaired in adherence and microcolony formation on cultured cells. An E. coli K-12 strain harbouring the EPEC H6 fliC gene on a plasmid showed discrete adhering clusters on HeLa cells, albeit to less extent than the wild-type EPEC strain. Flagella purified from EPEC bound to cultured epithelial cells and antiflagella antibodies blocked adherence of several EPEC serotypes. We determined that eukaryotic cells in culture stimulate expression of flagella by motile and non-motile EPEC. Isogenic strains mutated in perA (a transcriptional activator), bfpA (a type IV pilin), luxS (a quorum-sensing autoinducer gene) and in the type III secretion genes were reduced for motility in Dulbecco's modified Eagle medium (DMEM) motility agar and produced none or few flagella when associated with epithelial cells. Growth of these mutants in preconditioned tissue culture medium restored motility and their ability to produce flagella, suggesting the influence of a signal provided by mammalian cells that triggers flagella production. This study shows for the first time that the flagella of EPEC are directly involved in the adherence of these bacteria and supports the existence of a molecular relationship between the two existing type III secretion pathways of EPEC, the EPEC adherence factor (EAF) plasmid-encoded regulator, quorum sensing and epithelial cells.

Bacterial Adhesion↗
PubMed2002

[Bacterial present in the xylem of coffee (Rubiaceae: coffea arabica) with "Crespera" disease].

"Crespera" is an infectious disease of coffee plants that affects both the coffee production and the economy of the coffee producer countries. This disease affects morphologically the plant: long and narrow leaves with wavy borders and marginal necrosis; strong chlorosis results in drying of the leave, and leads to bad conditions of the plant. The internodes are short, producing the appearance of multiple sprouts in the axial sprout, the flowers can turn greenish, and the plant can present branches with severe symptoms, and branches without apparent symptoms at the same time. As a result, the coffee bean production decreases strikingly. The aim of this work was to determine the occurrence of the possible causative agent in the coffee plants using transmission electron microscopy. Normal and infected plants were compared looking at the leaves, central vein, lateral veins and petiole. It was determined that xylematic vessels show the presence of gram negative bacilliform bacteria (of thick-wavy walls), with dimensions of 0.3-0.5 micron diameter and 1-4 microns, length. The control plants did not show bacteria in the xylem.

Coffee↗