Mutational analysis of human CEACAM1: the potential of receptor polymorphism in increasing host susceptibility to bacterial infection

A common overlapping site on the N-terminal IgV-like domain of human carcinoembryonic antigen (CEA)-related cell adhesion molecules (CEACAMs) is targeted by several important human respiratory pathogens. These include Neisseria meningitidis (Nm) and Haemophilus influenzae (Hi) that can cause disseminated or persistent localized infections. To define the precise structural features that determine the binding of distinct pathogens with CEACAMs, we have undertaken molecular modelling and mutation of the receptor molecules at previously implicated key target residues required for bacterial binding. These include Ser-32, Tyr-34, Val-39, Gln-44 and Gln-89, in addition to Ile-91, the primary docking site for the pathogens. Most, but not all, of these residues located adjacent to each other in a previous N-domain model of human CEACAM1, which was based on REI, CD2 and CD4. In the current studies, we have refined this model based on the mouse CEACAM1 crystal structure, and observe that all of the above residues form an exposed continuous binding region on the N-domain. Examination of the model also suggested that substitution of two of these residues 34 and 89 could affect the accessibility of Ile-91 for ligand binding. By introducing selected mutations at the positions 91, 34 and 89, we confirmed the primary importance of Ile-91 in all bacterial binding to CEACAM1 despite the inter- and intraspecies structural differences between the bacterial CEACAM-binding ligands. The studies further indicated that the efficiency of binding was significantly enhanced for specific strains by mutations such as Y34F and Q89N, which also altered the hierarchy of Nm versus Hi strain binding. These studies imply that distinct polymorphisms in human epithelial CEACAMs have the potential to decrease or increase the risk of infection by the receptor-targeting pathogens

Haemophilus influenzae oral whole cell vaccination for preventing acute exacerbations of chronic bronchitis

BACKGROUND: Acute bronchitis leading to ongoing exacerbations is a serious condition predisposed to by viruses, bacteria or environmental factors. It can be fatal. Antibiotic therapy is not particularly useful. An oral Haemophilus influenzae vaccine has been developed. OBJECTIVES: To assess the effects of an oral, monobacterial whole-cell, killed, nontypeable H. influenzae vaccine in protecting against recurrent acute episodes in chronic bronchitis. SEARCH STRATEGY: In this updated review, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2006), MEDLINE (1966 to January Week 4 2006), EMBASE (1990 to September 2005) and ISI Current Contents (2004 to May 2006). SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing the effects of the H. influenzae vaccine on patients with recurrent acute exacerbations of chronic bronchitis were included when there was overt matching of the vaccine and placebo groups on clinical grounds. DATA COLLECTION AND ANALYSIS: Three authors extracted data and assessed trial quality independently from original records and publications for incidence and severity of bronchitis episodes and carriage rate of nontypeable H. influenzae measured in the upper respiratory tract every three months following vaccination. MAIN RESULTS: Six trials were included in the study with a total of 440 participants. The vaccine reduced the incidence of bronchitic episodes at three months after vaccination (rate ratio is 0.69; 95% CI 0.41 to 1.14) and at six months after vaccination (rate ratio 0.82; 95% CI 0.62 to 1.09). If these results been statistically significant, they would have represented a reduction in acute bronchitic attacks for vaccinated individuals of 31% at three months, and 18% at six. The effect had disappeared by nine months.The severity of exacerbations in the treatment group, as measured by requirement to prescribe antibiotics, was likewise reduced by 58% at three months (Peto odds ratio = 0.42; 95% CI 0.16 to 1.13), and by 65% at six months (Peto odds ratio = 0.35; 95% CI 0.16 to 0.75). AUTHORS' CONCLUSIONS: Vaccinating patients with recurrent acute exacerbations of chronic bronchitis in the autumn may reduce the number and severity of exacerbations over the following winter. A large clinical trial is needed

Effects of bacterial products on enterocyte-macrophage interactions in vitro

We describe a coculture model of a human intestinal epithelial cell line and human peripheral blood monocytes in which monocytes differentiate into cells with features of resident intestinal macrophages. Caco-2 cells are grown on the lower surface of a semipermeable filter with pore size of 3μm (Transwells®) until they differentiate into enterocytes. Peripheral-blood monocytes are added and the co-culture incubated for two days. Monocytes migrate through the pores of the membrane, come into direct contact with the basolateral surfaces of the epithelial cell monolayer, and develop characteristics of resident intestinal macrophages including downregulation of CD14 expression and reduced pro-inflammatory cytokine responses (IL-8, TNF and IL-1β) to bacterial products. The apical application of lipopolysaccharide (LPS) and muramyl dipeptide (MDP) resulted in an increased number of integrated monocytes, but abrogated the downregulation of CD14 expression and the diminished cytokine responses. MDP also reduced tight-junctional integrity, whilst LPS had no effect. These data indicate that LPS and MDP have significant pathophysiological effects on enterocyte-monocyte interactions, and confirm other studies that demonstrate that enterocytes and their products influence monocyte differentiation. This model may be useful in providing insights into the interaction between monocytes, epithelial cells and intestinal bacteria in health and disease

Xylitol inhibits J774A.1 macrophage adhesion in vitro

The aim of this work was to evaluate the effect of xylitol on J774A.1 macrophage adhesion. Adhesion consisted of a three-hour interval, at room temperature, followed by washing and cell incubation at 37ºC/5% CO2/ 48h. Xylitol was used to treat the cells either before (for 24h) or after the cell incubation (for 48h) at 5% as final concentration in both the situations. It was found that xylitol was effective in preventing the adhesion in both the conditions in spite of the former being 100-fold greater and significant (p < 0.001). The results pointed to an important xylitol action on macrophage adhesion, which should be further investigated as an inflammatory control