INCREASED PROTEIN-KINASE-C ACTIVITY IN LOW-DENSITY EOSINOPHILS

Eosinophil heterogeneity is expressed in cell density, membrane recept ors and function. It has been observed that increases in some function al activities correlate with decreased sedimentation density in human eosinophils. However, the cellular mechanisms to explain the up-regula tion of eosinophil function have not been fully explored. Protein kina se C (PKC) is an important family of enzymes mediating signal transduc tion for a wide variety of functions in many different cell types. Cha nges in the activity of PKC could explain some of the observed differe nces in function. In these experiments, PKC activity of human granuloc yte lysate supernatants was measured as the phosphatidyl serine-depend ent transfer of P-32 from [gamma-P-32]ATP to a protein substrate under conditions of maximal stimulation; a measure of activatable PKC conce ntration. We observed that the activity present in eosinophils (87.2 /- 8.4 pmol PO4 incorporated into histone per minute per 10(6) cells, n = 30) was not significantly different from that of neutrophils assay ed under the same conditions (91.5 +/- 5.6 U, n = 31) but the percent of total activity that was phosphatidyl serine dependent was greater i n eosinophils (97 +/- 1% vs 81 +/- 1% for neutrophils, p = 0.001). Blo od eosinophils isolated from low density Percoll fractions had a highe r activity (120 +/- 16 U) than that found in the higher density cells from the same subjects (81 +/- 19 U, n = 9, p = 0.011). When eosinophi ls recovered from bronchoalveolar lavage (BAL) fluid after segmental A g challenges were assayed, the PKC activity of BAL eosinophils was sim ilar to that of blood-derived eosinophils of equal density and low den sity BAL eosinophil PKC tended to be equal to or greater than higher d ensity cells. The beta isozyme of PKC but not the alpha or gamma was d etected in eosinophils by Western blotting with isozyme-specific mAb. These data indicate that eosinophil PKC activity is primarily caused b y the beta-isozyme, is related to cell density in blood-derived cells, and may have a relationship to cell function.