166
E . N. W I L L M E R
V I I I . LESSONS FROM T H E M E T A P L A S I A OF
MAEGLERIA
This is not the place to review the evidence of these controversial
matters or to express an opinion, but it is perhaps relevant to call
attention to the somewhat parallel behaviour of the protozoan Mastigamoeba, Maegleria gruberi. This is a soil-inhabiting amoeboid organism
which has two functional forms, one amoeboid and phagocytic, the other
flagellate and free-swimming. It changes from one form into the other
under the influence of the ionic composition of the medium. Dilute media,
bicarbonate and lactate ions, and high temperatures, favour the flagellate form; concentrated media, acidity, Na, K, N H 4 , Ca and M g ions
favour the amoeboid form. There is increasing evidence that the two
forms of cell are differently organized with respect to the maintenance
of their ionic equilibrium. Thus the flagellate form is adopted when the
cell has to keep water out and needs to conserve and collect Na and/or
K ions from its surroundings. The amoeboid form is adopted when the
organism needs to conserve water but when Na and K present no
problem except that of their excretion. The relevant point here, however, is that this organism can, in spite of these very fundamental
differences in organization and behaviour, in a matter of not more than
a few hours, or less in the case of the flagellate to amoeboid transformation, switch over reversibly from one form to the other (Willmer, 1956,
1958). The changes from macrophage to fibroblast and vice versa, if
they occur, must be changes which are just as radical and probably
of rather similar character to those which occur so readily in this
Protozoon.
If we are right in supposing that mechanocytes and amoebocytes,
being derived from two differently polarized epithelial cells, are
mutually opposed to each other, then the parallel with JVaegleria is
quite strong and the change in character which can be induced readily
in JVaegleria by appropriate changes in its environment can perhaps be
phosphatase, rapid pinocytosis, phagocytosis and the segregation of
vital dyes, especially neutral red and trypan blue, would all tend to
establish the identity of a cell as a macrophage, especially if the cell
showed an avoiding reaction with respect to other cells of its kind.
There are at least a dozen characteristics in all by which mechanocytes
differ from amoebocytes, so the case for making a distinction between
them is a strong one. Nevertheless, rapid changes of form and function
are not unknown elsewhere, and a change in the character of the cell
surface could, for instance, produce drastic consequential changes in
many other properties.
E . N. W I L L M E R
V I I I . LESSONS FROM T H E M E T A P L A S I A OF
MAEGLERIA
This is not the place to review the evidence of these controversial
matters or to express an opinion, but it is perhaps relevant to call
attention to the somewhat parallel behaviour of the protozoan Mastigamoeba, Maegleria gruberi. This is a soil-inhabiting amoeboid organism
which has two functional forms, one amoeboid and phagocytic, the other
flagellate and free-swimming. It changes from one form into the other
under the influence of the ionic composition of the medium. Dilute media,
bicarbonate and lactate ions, and high temperatures, favour the flagellate form; concentrated media, acidity, Na, K, N H 4 , Ca and M g ions
favour the amoeboid form. There is increasing evidence that the two
forms of cell are differently organized with respect to the maintenance
of their ionic equilibrium. Thus the flagellate form is adopted when the
cell has to keep water out and needs to conserve and collect Na and/or
K ions from its surroundings. The amoeboid form is adopted when the
organism needs to conserve water but when Na and K present no
problem except that of their excretion. The relevant point here, however, is that this organism can, in spite of these very fundamental
differences in organization and behaviour, in a matter of not more than
a few hours, or less in the case of the flagellate to amoeboid transformation, switch over reversibly from one form to the other (Willmer, 1956,
1958). The changes from macrophage to fibroblast and vice versa, if
they occur, must be changes which are just as radical and probably
of rather similar character to those which occur so readily in this
Protozoon.
If we are right in supposing that mechanocytes and amoebocytes,
being derived from two differently polarized epithelial cells, are
mutually opposed to each other, then the parallel with JVaegleria is
quite strong and the change in character which can be induced readily
in JVaegleria by appropriate changes in its environment can perhaps be
phosphatase, rapid pinocytosis, phagocytosis and the segregation of
vital dyes, especially neutral red and trypan blue, would all tend to
establish the identity of a cell as a macrophage, especially if the cell
showed an avoiding reaction with respect to other cells of its kind.
There are at least a dozen characteristics in all by which mechanocytes
differ from amoebocytes, so the case for making a distinction between
them is a strong one. Nevertheless, rapid changes of form and function
are not unknown elsewhere, and a change in the character of the cell
surface could, for instance, produce drastic consequential changes in
many other properties.