Protein kinase C (PKC) isotype profile in eosinophils from ponies with sweet itch and role in histamine-induced eosinophil activation

Eosinophils have been implicated in the pathogenesis of the seasonal equine allergic skin disease, sweet itch. Protein kinase C (PKC) is involved in regulating eosinophil function and antigen challenge has been reported to alter PKC isotype expression in blood eosinophils from allergic human subjects. Here we have compared the pattern of PKC isotype expression in eosinophils from sweet itch ponies with that in cells from normal ponies both during the active and inactive phases of the disease. A role for PKC in histamine-induced eosinophil activation was also investigated. Conventional PKCs alpha and beta, novel PKCs delta and epsilon and atypical PKCs iota and zeta were identified in eosinophils pooled from four allergic ponies during the inactive phase, when no clinical signs were evident. The PKC isotypes, like those in eosinophils from normal ponies, were located primarily in the particulate fraction of the cell. Isotype expression in cells from normal and allergic animals did not appear to be different. In contrast, during the active phase of the disease, when the sweet itch ponies had clinical signs, the expression of PKCs beta, epsilon and iota in eosinophils from these animals appeared to be increased relative to that in cells from normal ponies. When PKC expression in eosinophils from five individual normal and sweet itch ponies was compared, small, but statistically significant, increases in PKC epsilon and PKCdelta expression were evident in eosinophils from the sweet itch ponies during the active and inactive phases, respectively. The non-selective PKC inhibitors, staurosporine and Ro31-8220, significantly reduced histamine-induced superoxide production. Use of G?6976, an inhibitor of conventional PKCs, suggested that PKCalpha and/or beta were involved and that there was significantly greater inhibition of the response in eosinophils obtained from sweet itch ponies during the active phase. There was no significant difference in histamine-induced superoxide production by eosinophils from allergic and normal ponies and the functional significance of the increased PKC isotype expression in eosinophils from sweet itch ponies relative to that in cells from healthy animals remains to be established.