Frequencies of interleukin-5 mRNA-producing cells in healthy individuals and in immunoglobulin-deficient patients, measured by in situ hybridization

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Abstract
Interleukin‐5 (IL‐5) has previously been demonstrated to enhance immunoglobulin synthesis, especially IgA. Thus, it could be hypothesized that a defect production of IL‐5 may cause immunoglobulin deficiency. We have analysed the frequency of IL‐5 mRNA‐producing cells in healthy adults and in patients with common variable immunodeficiency or selective IgA deficiency. Unstimulated lymphocytes were rarely found to synthesize IL‐5 as measured by in situ hybridization. However, pokeweed mitogen and several other activating ligands induced the synthesis of IL‐5 mRNA in peripheral blood and spleen lymphocyte cultures. After pokeweed mitogen activation, the number of IL‐5 mRNA‐producing cells most often peaked on day 3 with a maximal frequency of around 1–2% of mononuclear cells. In a kinetic study we were unable to detect any peak frequency differences between healthy controls (mean 0.44%) and 20 patients (mean 0.58%), Thus, although IL‐5 has been reported to be an important regulator of IgA synthesis, a defect production does not seem to be the underlying mechanism in human immunoglobulin deficiency.