We have shown previously that intracellular phagosome movement require
s microtubules. Here we provide evidence that within cells phagosomes
display two different kinds of microtubule-based movements in approxim
ately equal proportions, The first type occurs predominantly in the ce
ll periphery, often shortly after the phagosome is formed, and at spee
ds below 0.1 mu m/second. The second is faster (0.2-1.5 mu m/second) a
nd occurs mainly after phagosomes have reached the cell interior. Trea
ting cells with nanomolar concentrations of taxol or nocodazole alters
microtubule dynamics without affecting either total polymer mass or m
icrotubule organisation. Such treatments slow the accumulation of phag
osomes in the perinuclear region and reduce the number of slow movemen
ts by up to 50% without affecting the frequency of fast movements, Thi
s suggests that a proportion of slow movements are mediated by microtu
bule dynamics while fast movements are powered by microtubule motors,
In macrophages, interphase microtubules radiate from the microtubule o
rganising centre with their plus-end towards the cell periphery To und
erstand the behaviour of 'early' phagosomes at the cell periphery we i
nvestigated their ability to bind microtubule plus-ends in vitro, We s
how that early phagosomes have a strong preference for microtubule plu
s-ends, whereas 'late' phagosomes do not, and that plus-end affinity r
equires the presence of microtubule-associated proteins within cytosol
, We suggest that phagosomes can bind to the plus-ends of dynamic micr
otubules and move by following their shrinkage or growth.