Torbjørn Bjerke

Atopic dermatitis: a total genome-scan for susceptibility genes

Atopic dermatitis is one of the most common chronic diseases of childhood and closely related to other clinical manifestations of allergy. The incidence is high and still increasing. The genetic contribution to disease development is substantial and complex. Only recently genetic research has begun to focus on this phenotype, and specific susceptibility genes remain to be found. To identify candidate regions holding genes for atopic dermatitis we performed a genome-scan in Danish affected sib-pair families containing sib-pairs matching a phenotype definition of both clinical atopic dermatitis and confirmed specific allergy. The scan was undertaken using 446 microsatellite markers and non-parametric linkage results were obtained from the MAPMAKER/SIBS computer program. We found evidence of linkage to three candidate regions in chromosomes 3p (MLS=2.14), 4p (MLS=2.00) and 18q (MLS=2.25), one of which has not been reported previously. Eight additional regions showed weaker but positive results.

Allergic rhinitis - a total genome-scan for susceptibility genes suggests a locus on chromosome 4q24-q27

Allergic rhinitis is a common disease of complex inheritance and is characterised by mucosal inflammation caused by allergen exposure. The genetics of closely related phenotypes such as asthma, atopy and to some extend atopic dermatitis has attracted attention in recent years. Genetic reports of allergic rhinitis on the contrary have as yet been most sparse. To identify candidate regions holding genes for allergic rhinitis we performed a total genome-scan on affected sib-pair families. From 100 Danish sib-pair families selected for allergy, families containing sib-pairs matching a phenotype definition of both clinical allergic rhinitis and confirmed specific allergy were chosen. Thirty-three affected sib-pair families qualified for the scan that was undertaken using 446 microsatellite markers. Non-parametric linkage results were obtained from MAPMAKER/SIBS computer program. The study revealed one major candidate region on chromosome 4q24-q27 (LOD=2.83) and eight minor candidate regions 2q12-q33, 3q13, 4p15-q12, 5q13-q15, 6p24-p23, 12p13, 22q13, and Xp21 (LOD=1.04–1.63) likely to contain susceptibility genes for allergic rhinitis. Our findings did not support a previous report of linkage of allergic rhinitis to chromosome 12q14-q24 but they added positive evidence to the asthma and atopy candidate regions 2q33 and 6p23. Further identification of the specific genes involved in allergic rhinitis will give opportunities for improved diagnosis and treatment.

Purification of human blood basophils by negative selection using immunomagnetic beads

A simple and rapid method for isolating highly purified and functionally intact basophils from normal human blood is described. Blood from healthy volunteers was centrifuged through a two layer Percoll density gradient. The majority of the basophils were recovered between Percoll layers with densities of 1.070 and 1.080, constituting 45.6% of total leukocytes. Lymphocytes, monocytes and neutrophils were extracted from this fraction using a panel of mabs in a direct or indirect selection procedure using immunomagnetic beads (Dynabeads) coated with sheep anti-mouse IgG. These negative immunoselection procedures produced a high yield of basophils with a mean purity of 97.8% (range 93.0-99.5%) and 97.0% (range 96.2-99.0%) using the direct and indirect method, respectively. The cells isolated by this method are viable, release histamine to various stimuli in a normal manner, and appear morphologically normal in transmission electron microscopy.

No linkage and association of atopy to chromosome 16 including the interleukin‐4 receptor gene

Background: Several susceptibility genes for atopy have been suggested in recent years. Few have been investigated as intensively as the interleukin‐4‐receptor α (IL4Rα) gene on chromosome 16. The results remain in dispute. Therefore, in a robust design, we tested for association of type I allergy to the IL4R variations I50V and Q576R, and investigated chromosome 16 for atopy candidate regions in general.

Histamine Release from Cord Blood Basophils

The histamine release (HR) after challenge with anti-IgE, concanavalin A, N-formyl-met-leu-phe and the calcium ionophore A23187 from 97 cord blood samples was determined by a microfiber-based assay. Maximum HR with anti-IgE showed great inter-individual variation (median: 20.5; range: 1-104 ng/ml blood), but was not significantly different from the results obtained in identically treated blood samples from 50 adults (median: 23; range: 1-93 ng/ml blood). Both the maximum HR and the sensitivity to anti-IgE were dependent on total plasma IgE content. Blood samples with plasma IgE greater than or equal to 0.5 IU/ml (n = 15) had significantly higher maximum HR than those with plasma IgE less than 0.5 IU/ml (n = 82; median: 32 vs. 18 ng/ml blood; p less than 0.01). Passive sensitization with IgE-rich atopic plasma increased the maximum HR with anti-IgE only in samples with a plasma IgE content of less than 0.5 IU/ml, although sensitivity to anti-IgE was universally increased. Preincubation with pharmacologic agents modulating the IgE-mediated HR produced effects generally similar to previous findings in adult blood. However, the effects of inhibiting the cyclooxygenase pathway in cord blood differed from our observations in adult blood, and may represent a maturational phenomenon. The family history of allergy was obtained by a questionnaire, and clinical observations were gathered from patient records. None of these parameters were found to influence HR with any secretagogue. However, HR stimulated by the calcium ionophore A 23187 was found to be highly dependent on the storage time of the EDTA-anticoagulated blood samples, which should be carefully controlled.

Basophil histamine release induced by anti-IgE and concanavalin A Relation to the total plasma IgE content

The plant lectin concanavalin A (Con A) has been shown to induce basophil histamine release by an IgE‐receptor‐dependent process resembling that of anti‐IgE‐antibodies.

Renal Tubular Uptake of Protein: Effect of pH

The present study was performed to determine to what extent pH influences protein reabsorption in renal proximal tubule cells. Rat surface proximal tubules were microinfused in vivo with 125I-labelled albumin in buffer solutions at different pHs. Tubular uptake was determined as the difference between microinfused and urinary trichloroacetic acid-precipitable radioactivity. In separate experiments the tubular uptake was followed by electron microscope autoradiography. The results showed that the uptake at pH 4.5 and 6.0 was about 15% higher as compared to uptake at pH 7.4. Furthermore, the electron microscope autoradiography demonstrated that albumin is taken up by endocytosis at acid pH as under normal conditions.

Regulation of FcepsilonARI synthesis in human eosinophils.

FcεRI, the high–affinity receptor for IgE, and eosinophils are thought to be key components of the allergic reaction underlying asthma and rhinitis. We provide evidence at the protein level that FcεRI is expressed in human blood eosinophils, and that the synthesis of FcεRI in purified human blood eosinophils is regulated by fibronectin in combination with IgE, IL–4, both involved in allergic reactions, and by RANTES, a strong chemotactic agent for eosinophils. This provides further evidence for a regulatory effect of IgE on human eosinophils in allergic disease.