Ultrastructural localization of the Charcot-Leyden crystal protein (lysophospholipase) to granules and intragranular crystals in mature human basophils.

Human blood basophils have been shown to form Charcot-Leyden crystals (CLC) and to contain quantities of CLC protein comparable to the eosinophil (Ackerman SJ, Weil GJ, Gleich GJ, J Exp Med 155:1597, 1982). We examined the subcellular localization of CLC protein in human basophils from peripheral blood using an ultrastructural postembedding immunogold method and affinity chromatography-purified polyclonal primary antibody to purified human eosinophil CLC protein. We found CLC protein to be uniquely associated with the main, large, particle-filled granule population of human basophils and particularly within intragranular Charcot-Leyden crystals in these granules. Rarely, CLC protein was localized within small, smooth perigranular vesicles. Neutrophils, lymphocytes, and monocytes present in preparations stained for the CLC protein were negative as were controls for the specificity of the immunogold staining. Mature eosinophils contained small numbers of positive crystalloid-free primary granules, as previously reported (Dvorak AM, Letourneau L, Login GR, Weler PF, Ackerman SJ, Blood 72:150, 1988). The presence of CLC protein in hexagonal and pyramidal crystals regularly present in activated types II and III basophils suggests two possibilities currently being investigated. Like eosinophils, basophils could synthesize CLC protein, or eosinophil-derived CLC protein could be internalized and stored in basophil granules. Regardless of the mechanism for acquisition of CLC protein (lysophospholipase) by basophils, the identification and subcellular localization of this enzyme in basophils requires that it be considered in basophil cell biology as well as in the pathobiology of basophil-rich reactions.