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Hydrocortisone enhances total IgE levels—but not the synthesis of allergen‐specific IgE—in a monocyte‐dependent manner

Recently, hydrocortisone (HC), when combined with human IL‐4, has been reported to increase IgE levels in supernatants (SN) of in vitro cultured leucocytes. In this study we investigated the influence of HC on allergen‐specific IgE synthesis. Moreover, we examined the relevance of different cell types in this respect. Peripheral blood mononuclear cells (PBMC), T cell‐depleted PBMC, CD14‐depleted PBMC and highly purified B cells from 10 allergic (birch pollen and/or grass pollen) patients and five non‐allergic individuals were investigated. The cells were incubated with HC and/or recombinant human IL‐4 (rIL‐4) for 8 days. A considerable increase of total IgE was observed in HC/rIL‐4‐stimulated cultures compared with rIL‐4 alone, HC alone or non‐stimulated cultures. We demonstrate that this effect depends on the presence of monocytes in in vitro cultures. These results were seen in every experiment, irrespective of healthy or atopic state of the blood donor. The increase of IgE could not be attributed to a rise of birch pollen‐ and/or grass pollen‐specific IgE in patients allergic to these allergens, as shown by IgE‐immunoblot. Radioallergosorbent test (RAST) investigations of HC/rIL‐4‐stimulated cell cultures from allergic and non‐allergic patients confirmed that HC/rIL‐4‐induced elevated IgE production was also not due to increased production of IgE, specific for important aero‐allergens (pollens, house dust mite or animal dander). Therefore we conclude that newly synthesized IgE is not specific for allergens, but that sequential isotype switching in human B cells leads to increased polyclonal IgE production.