An investigation into IgE-facilitated allergen recognition and presentation by human dendritic cells

Background

Allergen recognition by dendritic cells (DCs) is a key event in the allergic cascade leading to production of IgE antibodies. C-type lectins, such as the mannose receptor and DC-SIGN, were recently shown to play an important role in the uptake of the house dust mite glycoallergen Der p 1 by DCs. In addition to mannose receptor (MR) and DC-SIGN the high and low affinity IgE receptors, namely FcϵRI and FcϵRII (CD23), respectively, have been shown to be involved in allergen uptake and presentation by DCs.

Objectives

This study aims at understanding the extent to which IgE- and IgG-facilitated Der p 1 uptake by DCs influence T cell polarisation and in particular potential bias in favour of Th2. We have addressed this issue by using two chimaeric monoclonal antibodies produced in our laboratory and directed against a previously defined epitope on Der p 1, namely human IgE 2C7 and IgG1 2C7.

Results

Flow cytometry was used to establish the expression patterns of IgE (FcϵRI and FcϵRII) and IgG (FcγRI) receptors in relation to MR on DCs. The impact of FcϵRI, FcϵRII, FcγRI and mannose receptor mediated allergen uptake on Th1/Th2 cell differentiation was investigated using DC/T cell co-culture experiments. Myeloid DCs showed high levels of FcϵRI and FcγRI expression, but low levels of CD23 and MR, and this has therefore enabled us to assess the role of IgE and IgG-facilitated allergen presentation in T cell polarisation with minimal interference by CD23 and MR. Our data demonstrate that DCs that have taken up Der p 1 via surface IgE support a Th2 response. However, no such effect was demonstrable via surface IgG.

Conclusions

IgE bound to its high affinity receptor plays an important role in Der p 1 uptake and processing by peripheral blood DCs and in Th2 polarisation of T cells.

Cross-reacting antibodies enhance dengue virus infection in humans

Dengue virus co-circulates as four serotypes, and sequential infections with more than one serotype are common. One hypothesis for the increased severity seen in secondary infections is antibody-dependent enhancement (ADE) leading to increased replication in Fc receptor-bearing cells. In this study, we have generated a panel of human monoclonal antibodies to dengue virus. Antibodies to the structural precursor-membrane protein (prM) form a major component of the response. These antibodies are highly cross-reactive among the dengue virus serotypes and, even at high concentrations, do not neutralize infection but potently promote ADE. We propose that the partial cleavage of prM from the viral surface reduces the density of antigen available for viral neutralization, leaving dengue viruses susceptible to ADE by antibody to prM, a finding that has implications for future vaccine design.

Studying General Practice in the Inner City — A Model for Linking Available Sources of Data: Preliminary Communication

The effect of implementing proposals intended to improve general practice primary care in inner London is not known. To test it requires a model of how general practice works and methods of measuring appropriate variables. The methods must be sufficiently simple to allow measurement prior to, as well as during, change. This paper presents such a model, describes methods used to measure some of those variables, and illustrates the results.