Interleukin 3-dependent mediator release in basophils triggered by C5a.

Abstract

Basophils and mast cells are important effector cells of inflammation and in particular of acute allergic reactions. Basophils can be activated to release inflammatory mediators by IgE-dependent and IgE-independent stimuli (1-4). The mediator profile produced by basophils strongly depends upon the agonist used to activate the cells (4a) . For example, crosslinking ofhigh-affinity IgE-receptors by an antigen, anti-IgE or anti-receptor antibodies leads to the release of preformed mediators from granule stores, like histamine and proteolytic enzymes, and also results in the activation of enzymes (phospholipase[s] and 5-lipoxygenase) responsible for the generation of leukotriene C4 (LTC 4),' a very potent lipid mediator and smooth muscle contractant (6). Conversely, the anaphylatoxin C5a, which at low concentrations is a potent inducer of basophil degranulation, does not activate basophils to produce bioactive lipids . These observations clearly indicate that degranulation and the generation of the arachidonic acid metabolite LTC4 are dissociated events and therefore controlled by different mechanisms .Granulocyte/macrophage colony-stimulating factor (GM-CSF) is a pluripotent growth factor for myeloid bone marrow precursors (7,8), but more recent studies demonstrated that this cytokine also enhances the function (in particular cytotoxicity and oxygen radical release) of mature inflammatory effector cells, like monocytes, eosinophils, and neutrophils (PMN) (9-13). Studies from our laboratory demonstrated that PMN sequentially exposed to GM-CSF and the chemotactic peptides C5a or FMLP release relatively large amounts of LTB4 and LTB4 metabolites, while neither peptide alone triggers the formation of these lipid mediators (14). Preexposure of PMN to GM-CSF also results in a strong enhancement of chemotactic peptide-dependent generation ofplatelet-activating factor, another potent lipid mediator (15). From these experiments we concluded that GM-CSF not only enhances effector cell functions, but also qualitatively changes in the mediator profile of the neutrophils triggered by diverse agonists .These observations suggested that other growth-promoting cytokines may also modify the mediator profile of mature leukocytes, and we thus studied the effects of IL-3 on blood basophils. IL-3 stimulates the growth of early progenitor cells of

Dual Phase Priming by IL-3 for Leukotriene C4 Generation in Human Basophils: Difference in Characteristics Between Acute and Late Priming Effects

“…8Bb). The generation of free AA/LTC 4 is rapid and complete within 45 s, which is consistent with the nature of a transient increase in [Ca 2ϩ ] i following C5a stimulation (it returns to the basal level within 45 s) (12,13). In the current studies we have shown that the overlap in the two events was also adjusted by treatment of IL-3 for 18 h, but by a different mechanism.…”

“…Basophils are the major, if not sole, leukocytes to release histamine and to generate LTC 4 in response to a combination of IL-3 and C5a, and IL-3 affects the basophil response directly (13). We also confirmed that basophils were the major source of LTC 4 release stimulated by IL-3 (for 15 min or 18 h) plus C5a under our experimental conditions (see Results).…”

“…Kurimoto et al (13) previously demonstrated that basophils are the major, if not sole, leukocytes to generate LTC 4 in response to a combination of IL-3 (early effects) and C5a, and IL-3 affects the basophil response directly. To confirm these results under our experimental conditions we also examined LTC 4 release from pure (70 -96%) and impure (6%) basophil suspensions (from the same donor preparations) in response to combinations of IL-3 (15 min or 18 h) and C5a.…”

“…However, the treatment with IL-3 for 15 min or overnight (18 -24 h) enables C5a to induce a significant amount of LTC 4 (11)(12)(13). The kinetic characteristics of this priming effect were examined.…”

“…C5a is an excellent secretatgogue for histamine release, but for basophils from most donors it does not induce LTC 4 release (11)(12)(13). A 5-min preincubation of the cells with IL-3 permits C5a to induce marked LTC 4 release (12,13).…”