| Abstrakt: |
Human neutrophils stimulated with immune complexes in the presence of platelets show enhanced superoxide anion (O2-.) responses that are proportional to the amount of agonist present and the number of platelets added. Platelet related enhancement of O2-. responses also occurs with the neutrophil agonists phorbol ester, formyl chemotactic peptide and zymosan particles. Pretreatment of platelets with cycloheximide does not alter their ability to enhance O2-. responses of neutrophils. In parallel with platelet-related enhancement of O2-. responses of immune complex-stimulated neutrophils, secretory release of myeloperoxidase is also increased. The platelet effects on O2-. responses can be reproduced with platelet lysates or with supernatant fluids which have been obtained from thrombin or immune complex-stimulated platelets and are rich in ATP and ADP content. Solutions containing ATP and ADP in amounts similar to those found in supernatant fluids of activated platelets reproduce the enhancement of O2-. responses in N-formyl methionyl leucyl phenylalanine (FMLP) or immune complex-activated neutrophils. The platelet factor responsible for the effects of neutrophils is heat-stable, elutes in gel sieving chromatography near the position of phenol red and does not, in the absence of a neutrophil agonist, trigger an O2-. response. With formyl peptide-stimulated neutrophils, ATP and ADP enhance O2-. responses while the responses are depressed by addition of AMP or adenosine. In immune complex-stimulated neutrophils, adenosine and all adenine nucleotides enhance the O2-. responses. Taking advantage of this information, treatment of ATP or of supernatant fluids from thrombin-stimulated platelets with alkaline phosphatase (resulting in formation of adenosine) converts the O2-. enhancing activity for formyl peptide-activated neutrophils into an inhibitory activity. In contrast, using immune complex-activated neutrophils, similar manipulations of ATP or supernatant fluids from stimulated platelets result only in enhanced O2-. responses. These data support the conclusion that the platelet-derived factor responsible for enhanced O2-. responses in neutrophils is ATP/ADP. In FMLP stimulated neutrophils, the presence of ATP or ADP leads to enhanced increases in intracellular levels of Ca++ as determined by the fura-2 probe, while the presence of AMP or adenosine results in inhibition of the increases in FMLP induced elevations in cytosolic Ca++. These data demonstrate a direct relationship between effects of adenine compounds on FMLP induced changes in cytosolic Ca++ and the associated O2-. responses. |
