T cell functions

Mitogen responsiveness in reptiles was first described in Alligator mississippiensis by Cuchens and Clem, whereby PBLs were shown to respond by powerful proliferation to concanavalin A (Con A) and lipo-polysaccharide. Significant Con A-mediated mitogen-esis is consistently observed in thymocytes, spleen cells and PBLs of lizards and snakes. Acute graft-ver-sus-host reaction is readily induced in newly hatched (or born) turtles and lizards following intraperitoneal injection with spleen cells from adult allogeneic donors. Reptilian lymphocytes are also able to respond powerfully to alloantigenic cells in the mixed leukocyte reaction (MLR). Significant responses are obtained in 50-90% of random MLR cultures performed, depending on the species examined, culture conditions and putative major histocompatibility complex (MHC) gene differences between responder and stimulator. Data gathered in several species suggest that the lymphocyte activating determinants in MLR are not extremely polymorphic in reptiles. Most importantly, seasonal and other environmental parameters, including captivity, malnutrition, etc., have an extremely strong impact on reptilian T cell functions. Deterioration in these ambient factors is paralleled by significant impairment, up to complete abrogation, of the different aspects of T cell responsiveness. So, in inadequate seasonal and laboratory conditions mitogen and MLR responsiveness is abolished (Tables 1 and 2). The severe impact of ambient factors on T cell functions, together with the putative low polymorphism of reptilian MHC class I/II loci, may explain why chronic graft rejection was thought to be the rule in reptiles. But in optimal seasonal conditions, a significant proportion of lizards and snakes reject skin allografts in the acute manner typical of mammals (Table 3). Anamnestic responses characterized by an earlier onset and a more rapid rejection time are invariably observed. These findings indicate that reptiles display the major functional markers of the

Table 1 Lizard lymphoproliferative responses to Con A and in MLRa

Table 2 Snake lymphoproliferative responses to Con A and in MLR"

Table 1 Lizard lymphoproliferative responses to Con A and in MLRa

Season

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