Charcot‐Leyden crystal protein in the degranulation and recovery of activated basophils

The Charcot‐Leyden crystal (CLC) protein, a prominent cell constituent unique to eosinophils and basophils, possesses lysophospholipase activity. This activity and the extracellular deposition and formation of CLC in tissues and body fluids in association with eosinophils suggest an extracellular function for this protein in inflammation. During degranulation, basophils release granule‐derived mediators of inflammation. We postulated that CLC protein, localized in part to the basophil granule, might be released along with other mediators during this process. The extracellular release of CLC protein was studied during the degranulation of basophils stimulated by anti‐immunoglobulin E (anti‐IgE), N‐formyl‐methionyl‐leucyl‐phenylalanine (fMLP), phorbol myristate acetate, eosinophil major basic protein (MBP), and calcium ionophore A23187. Histamine release was used as a marker of basophil degranulation; its release was measured utilizing the fluorometric technique. CLC protein was not released into the supernatant during this process as determined by radioimmunoassay. CLC protein in the extracellular space, either as intact crystals or aggregates, was undetectable by indirect immunofluorescent staining of basophils activated with either anti‐IgE or fMLP. However, upon activation, the immunofluorescent cytoplasmic and nuclear staining pattern for CLC protein was significantly altered. Decreased cytoplasmic staining and persistent or increased nuclear staining for CLC protein were observed after activation, with recovery of the preactivation, unstimulated cellular staining pattern at 30 and 45 min after stimulation with fMLP and anti‐IgE, respectively. These findings suggest that CLC protein functions intracellularly in basophils during the process of activation, degranulation, and recovery. The potential nuclear function(s) of this lysophospholipase in the basophil requires further investigation.