78
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
et al. (196613) in the tissue extracts of certain marine pelecypods.
Certainly the occurrence of ‘( immune-like ” substances in molluscs
which act against incompatible parasites is not widespread. I have
tested many such combinations and have found nothing suggestive of
innate immunity except that reported by Cheng et al. (196610).
Another observation which suggests acquired immune factors in
molluscs has been reported by Barbosa and Coelho (1956). These
workers have demonstrated that Australorbis glabratus previously
‘( cured ” of Schistosoma mansoni infection could be reinfected ; however, some tissue reaction is evoked in reinfected snails, a phenomenon
not usually found in initial infections (exceptions reported by Cheng
and Cooperman (1964), Probert and Erasmus (1965) and Cheng et al.
(1966a) have been cited earlier). Barbosa and Coelho’s observations
could mean that some type of acquired incomplete immunity exists
in A . glabratus after the initial infection and becomes manifested during
the reinfection as cellular response. These workers, however, have
found that the sera (plasma) of infected A. glabratus has no effect on
S. mansoni miracidia.
Recently, Michelson (1963b, 1964) has reported the existence of
S. mansoni miracidia-immobilizing substances in tissue extracts of
A. glabratus infected with this trematode.* I n 1964 he stated that seven
species of gastropods were used ; furthermore, in the case of Helisoma
caribaeum, six ( ( strains ” were employed. Although the extracts of
all the species, including uninfected Australorbis glabratus extract and
water, gave positive miracidial-immobilization, that brought about by
infected A . glabratus extract was significantly greater. Michelson
(1963b) reported his results on whether the miracidia-immobilizing
substances were specifically associated with S. mansoni. To this end,
he tested extracts of (1) snails infected with an acid-fast bacillus,
(2) snails infected with an echinostome metacercaria, (3) snails infected
with the nematode Daubaylia potomaca, (4) snails inoculated with
bovine albumin, ( 5 ) snails inoculated with Schistosoma mansoni eggs,
and (6) snails inoculated with polystyrene spheres. Immobilization of
miracidia was observed only in extracts of snails infected with D.
potomaca or lyophylized S. mansoni eggs. I n neither case, however,
did the percentage of immobilization reach the level observed in extracts
of S. mansoni-infected snails.
From the review presented above, it is evident that there are
evidences which support the concept that acquired humoral immunity
does exist, a t least in certain species of molluscs, although, needless t o
state, more direct evidences are required. Relative to the miracidia*See note on p. 389.
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
et al. (196613) in the tissue extracts of certain marine pelecypods.
Certainly the occurrence of ‘( immune-like ” substances in molluscs
which act against incompatible parasites is not widespread. I have
tested many such combinations and have found nothing suggestive of
innate immunity except that reported by Cheng et al. (196610).
Another observation which suggests acquired immune factors in
molluscs has been reported by Barbosa and Coelho (1956). These
workers have demonstrated that Australorbis glabratus previously
‘( cured ” of Schistosoma mansoni infection could be reinfected ; however, some tissue reaction is evoked in reinfected snails, a phenomenon
not usually found in initial infections (exceptions reported by Cheng
and Cooperman (1964), Probert and Erasmus (1965) and Cheng et al.
(1966a) have been cited earlier). Barbosa and Coelho’s observations
could mean that some type of acquired incomplete immunity exists
in A . glabratus after the initial infection and becomes manifested during
the reinfection as cellular response. These workers, however, have
found that the sera (plasma) of infected A. glabratus has no effect on
S. mansoni miracidia.
Recently, Michelson (1963b, 1964) has reported the existence of
S. mansoni miracidia-immobilizing substances in tissue extracts of
A. glabratus infected with this trematode.* I n 1964 he stated that seven
species of gastropods were used ; furthermore, in the case of Helisoma
caribaeum, six ( ( strains ” were employed. Although the extracts of
all the species, including uninfected Australorbis glabratus extract and
water, gave positive miracidial-immobilization, that brought about by
infected A . glabratus extract was significantly greater. Michelson
(1963b) reported his results on whether the miracidia-immobilizing
substances were specifically associated with S. mansoni. To this end,
he tested extracts of (1) snails infected with an acid-fast bacillus,
(2) snails infected with an echinostome metacercaria, (3) snails infected
with the nematode Daubaylia potomaca, (4) snails inoculated with
bovine albumin, ( 5 ) snails inoculated with Schistosoma mansoni eggs,
and (6) snails inoculated with polystyrene spheres. Immobilization of
miracidia was observed only in extracts of snails infected with D.
potomaca or lyophylized S. mansoni eggs. I n neither case, however,
did the percentage of immobilization reach the level observed in extracts
of S. mansoni-infected snails.
From the review presented above, it is evident that there are
evidences which support the concept that acquired humoral immunity
does exist, a t least in certain species of molluscs, although, needless t o
state, more direct evidences are required. Relative to the miracidia*See note on p. 389.