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since its modulated appearance on cell surfaces depends on
the removal of cells already expressing it at their
surface.
Development of Purified Cells
It is clear that A2B5(+) cells were recruited in
purified cultures. It is also clear that neurons appeared
in purified cultures when grown on a nonselective
substratum. Initially, the small proportion of identifiable
neurons present before separation were depleted by 83% as
evident by NF immunoreactivity. Degeneration of purified
cells on polyornithine also suggests that neurons were
depleted because no cells survived. Presumably, they would
have grown if they were present in the purified cells. This
degeneration occured even though the cells had become
A2B5(+). Thus, the presence of A2B5 antigen on a cell
surface does not in itself correlate with survival on
polyornithine. Microsphere fraction cells (A2B5(+)-
enriched), on the other hand, resulted in the visually most
dense network of neurons, which suggests that the majority
of neurons were A2B5(+).
When grown on a nonselective substratum such as glass
for  1-2 weeks there appeared to be no decrease in the
density of A2B5(+) neurons or of neurofilaments in purified
cultures as compared to unpurified monolayers. If the
purified A2B5(-) cells were initially devoid of the
majority of neurons as is suggested above, then, neurons