60
First and second-set skin allograft rejections (37,59) characteris
tic of T-cell reactions in mammals have also been demonstrated in rep
tiles with an anamnestic second-set response. However there is a major
difference between transplantation reactions of reptiles and mammals, in
that reptilian reactions are typically chronic (36,37) as opposed to the
acute rejections occuring in mammals. These data suggest that T-like
functions may differ from those in mammals. Indeed, graft rejection
sites in turtles and snakes are infiltrated very early not only with
lymphocytes and macrophages, but also with an abundance of plasma., cells
(11). This observation suggests that such chronic graft rejections may
be antibody-mediated rather than cellularly (via T-like cell) mediated.
Responses to haptens conjugated to protein carriers have also been
demonstrated in reptiles (8,73) although the hapten-carrier effect has
apparently not been studied. In brief, data demonstrating that reptiles
can 1) show a 19S to 7S switch, 2) produce anti-hapten antibodies,and 3)
undergo graft rejections are at best only circumstantial evidence for
the existence of a T-like cell in these species. In fact one could
conceivably (although perhaps not too convincingly) argue for the exist
ence of only B-like cells from the same data.
Many of the reports from previous In vivo experiments in which
humoral responses to antigenic challenge were tested conflicted with
one another and in some cases there were questions as to whether rep
tiles could respond to antigenic challenges at all (36). Many of these
discrepancies have since been attributed to differences in the tempera
tures at which the animals were maintained after immunization. As early
as 1901, Metchnikoff demonstrated that the alligator responded to diph
theria toxin by forming antitoxin if the alligators were maintained at