FIG. 7.

Effects of GM-CSF on the frequency of coiling phagocytosis by different human phagocytes. Human monocytes, neutrophils, and eosinophils (2 × 10⁶) isolated from the same individual (different from those represented in Fig. 6), were incubated with B. burgdorferi cells (2 × 10⁷) for 45 min in the presence or absence of GM-CSF (100 ng/ml) added 10 min before. The bars represent the relative frequencies of coiling and conventional phagocytosis with GM-CSF and without, determined by electron microscopy as described in Materials and Methods, given as means ± standard errors of the means of triplicate determinations. Essentially the same results were observed in two additional identically performed experiments with phagocytes from different donors, and the results shown are therefore considered to be representative. PMA and especially GM-CSF increase the frequency of coiling phagocytosis selectively. The stimulated frequencies of the different phagocyte populations peak at about the same level, although their spontaneous frequencies are quite different.