A number of aspects of the humoral and cellular immune
responses of the common dogfish Scyliorhinus canicula L.
were examined in order to define the immunological status
of the animal in relation to its phylogenetic origins.
The dogfish was shown to have the ability to produce
specific antibody in response to a variety of soluble and
particulate protein antigens. The existence of several
non-specific defence mechanisms was demonstrated including
a well established reticulo-endothelial system capable of
rapidly clearing injected foreign material from the blood
and also the bacteriolytic enzyme, lysozyme.
Specific antibody from the fish had marked
agglutinating properties which could be destroyed with
reducing agents but which could not be demonstrated to form
precipitin lines in agar gels. It could also fix
complement. Isolation and characterisation of the antibody
molecule showed it to have virtually neutral electrophoretic
mobility, a molecular weight of approximately 800,000 daltons
and a sedimentation coefficient of 18.6S. On reduction the
molecule was shown to comprise heavy and light polypeptide
chains with molecular weights of 76,000 and 18,000 daltons,
respectively. On the basis of these findings the antibody
was considered to be of the IgM class of immunoglobulin
found in higher vertebrates. This was the only
immunoglobulin found in the dogfish although an
antigenically identical protein with a molecular weight
of 160,000 daltons was also demonstrated and this was
considered to be a monomeric form of an IgM pentamer.
A survey of lymphoid tissues revealed that the fish
had a well developed spleen. This organ was also shown
to be directly involved in immunological reactions.
Conversely, the thymus was poorly developed and involuted
during an early stage in the life of the fish. Its
immunological contribution was not determined. Two other
tissues, the organ of Leydig and the epigonal tissue were
found to comprise a high proportion of poorly differentiated
lymphoid cells and these were considered to be similar to
the stem cells of the bone marrow found in mammals.
Ultrastructural examination of peripheral blood leucocytes
showed that they comprised populations of cells analagous,
to mammalian lymphocytes, plasma cells, granulocytes, and
monocytes. Using a specific antiserum and an immunofluorescence
technique, a high proportion of leucocytes were
revealed to have immunoglobulin determinants on their
surface.
In a number of experiments to investigate cellular
functions in vitro it was found that dogfish leucocytes
could be stimulated by a variety of mitogenic substances
but these results were insufficient to provide evidence
for lymphocyte heterogeneity. Evidence that the dogfish
was capable of weak recognition of histocompatibility
antigens was provided in vitro by mixed lymphocyte
cultures and in vivo by reaction to injected allogeneic
leucocytes.
Although several different techniques were used no
evidence of immediate hypersensitivity reactions could be
demonstrated. Delayed hypersensitivity was shown, however,
by the leucocyte migration inhibition test and possibly by
local skin reactions.
The immunological relationship of the dogfish to an
intestinal helminth parasite, Proleptus obtusus, was also
investigated. The fish was found to be capable of
producing antibody specific for the cuticle of the nematode.
The parasite could also invoke several cellular reactions
including the stimulation of leucocytes in vitro and
delayed but not immediate hypersensitivity