Fig. 3. Use of DCDHF as an oxidative indicator during phagocytosis. (a) Three DCDHF-conjugated zymosan particles are shown before and after addition of H₂O₂ (0.83 mM). The traces below show the time courses for the increase in fluorescence (SI=summated intensity) for the three particles with the arrow indicating the addition of H₂O₂. (b) The fluorescence intensity of internalised (arrowed) and adherent (asterisk) DCDHF-conjugated zymosan particles are compared. The DCDHF intensity image and the phase contrast image have been superimposed for clarity. (c) The dependence of the oxidation response on peroxidase activity is shown. The first two arrows show the addition of H₂O₂ (0.83 mM and 1.66 mM, respectively), enlarged in the inset figure. The third arrow shows the addition of horseradish peroxidase (0.25 units/ml), and then a further increase in H₂O₂ (2.49 mM). (d) A typical experiment in which FITC-conjugated zymosan particles were internalised is shown. The images show the internalisation of the particles and the graph shows the accompanying intensity change. This result was typical of four other experiments.