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IL-4 secretion and histamine release by human basophils are differentially regulated by protein kinase C activation
J T Schroeder1, B P Howard, M K Jenkens
1The Johns Hopkins University School of Medicine, Division of Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Baltimore, Maryland 21224, USA. schray@welchlink.welch.jhu.edu
Abstract:
The role of protein kinase C (PKC) activation was investigated in the secretion of interleukin-4 (IL-4) protein by human basophils. Phorbol myristate acetate (PMA) induced little to no detectable IL-4 protein in culture supernatants, despite being a potent secretagogue of histamine release by basophils. In fact, the secretion of IL-4 by basophils stimulated with ionomycin alone was down-regulated (30-70%) with the simultaneous addition of PMA. In peripheral blood lymphocytes (PBL), however, the combination of ionomycin and PMA were highly synergistic, resulting in maximum IL-4 release but at a slower rate. PKC inhibitors reversed these effects on IL-4 secretion. In sharp contrast to its inhibitory effect on IL-4 protein secretion, PMA did not block the accumulation of IL-4 mRNA in basophils activated by ionomycin. These data suggest that there are marked differences in the regulatory processes for IL-4 transcription, translation, or secretion between basophils and lymphocytes.
Insights
Protein kinase C (PKC) activation inhibits interleukin-4 (IL-4) protein secretion in human basophils, contrasting with its synergistic effect in lymphocytes. This suggests distinct regulatory mechanisms for IL-4 production in these cell types.
Area of Science:
- Immunology
- Cell Biology
Background:
- Interleukin-4 (IL-4) is a key cytokine in allergic responses and immune regulation.
- Human basophils and peripheral blood lymphocytes (PBL) are critical immune cells involved in inflammatory and adaptive immunity.
- Protein kinase C (PKC) is a family of enzymes involved in cell signaling pathways that regulate various cellular functions, including immune responses.
Purpose of the Study:
- To investigate the role of protein kinase C (PKC) activation in the secretion of interleukin-4 (IL-4) protein by human basophils.
- To compare the effects of PKC activation on IL-4 secretion in human basophils versus peripheral blood lymphocytes (PBL).
Main Methods:
- Human basophils and PBL were stimulated with ionomycin and/or phorbol myristate acetate (PMA), a PKC activator.
- IL-4 protein levels in culture supernatants were measured.
- IL-4 mRNA accumulation was assessed.
- PKC inhibitors were used to confirm the role of PKC signaling.
Main Results:
- PMA alone induced minimal IL-4 protein secretion from basophils, despite being a potent histamine secretagogue.
- PMA inhibited ionomycin-induced IL-4 secretion in basophils by 30-70%.
- In PBL, ionomycin and PMA acted synergistically to maximize IL-4 release, albeit at a slower rate.
- PKC inhibitors reversed the observed effects on IL-4 secretion.
- PMA did not inhibit the accumulation of IL-4 mRNA in ionomycin-activated basophils.
Conclusions:
- PKC activation plays a differential role in regulating IL-4 protein secretion between human basophils and lymphocytes.
- The inhibitory effect of PMA on IL-4 protein secretion in basophils suggests post-transcriptional or post-translational regulation.
- These findings highlight distinct mechanisms controlling IL-4 production and secretion in different immune cell types.