Chronic skin graft rejection in the Urodela. I. A comparative study of first- and second-set allograft reactions

Amphibian declines: an immunological perspective

Many, but not all, amphibian populations have been declining on all six continents on which they live. Although habitat destruction, direct application of toxicants, and introduction of predators/competitors are obvious causes of amphibian declines, many amphibians are dying of infectious diseases in relatively pristine habitats on several continents. In this paper, we review the patterns of these disease outbreaks and the characteristics of amphibian immune systems. Hypotheses are presented to explain the apparent susceptibility of amphibians to these pathogens. Natural and man-made factors that can alter amphibian immune responses to pathogens are discussed. Additional research is needed on the biology of the specific pathogens, the pattern of immune responses they elicit, and the nature of environmental stressors that may increase susceptibility to infectious disease.

Age-related changes in the tiger salamander retina

Tiger salamanders have been used in visual science because of the large size of their cells and the ease of preparation and maintenance of in vitro retinal preparations. We have found that salamanders over 27 cm in length show a variety of visual abnormalities. Compared to smaller animals (15-23 cm), large animals exhibited a decrease in visual responses determined by tests of the optomotor reflex. Small animals responded correctly an average of 84.5% of the time in visual testing at three light levels compared to an average of 68.4% for the large animals with the poorest visual performance at the lowest level of illumination. In addition, large animals contained (i) histological degeneration of the outer retina, in particular, loss and disruption of outer segments and abnormalities of the retinal pigmented epithelium, (ii) loss of cells, including photoreceptors, by apoptosis as evaluated with the TUNEL technique, and (iii) an increase in the number of macrophages and lymphocytes within the retina as determined by morphological examination. These histological changes were present in all large animals and all quadrants of their retinas. In contrast, small animals showed virtually no retinal degeneration, no TUNEL-positive cells, and few immune-like cells in the retina. Since large animals are also older animals. the visual changes are age-related. Loss of visual function and histological degeneration in the outer retina also typify aged human eyes. Thus, we propose that large salamanders serve as an animal model for age-related retinal degeneration. In addition to providing a source of aging retina that is readily accessible to experimental manipulation, the salamander provides a pigmented retina with a mixed (2:1, rod:cone) population of photoreceptors, similar to the degeneration-prone parafoveal region of the human eye.

Mitogen-activated axolotl (Ambystoma mexicanum) splenocytes produce a cytokine that promotes growth of homologous lymphoblasts

Culture supernatants (PHA-SNs) from axolotl splenocytes cultured with phytohemagglutinin-P (PHA) in medium supplemented with bovine serum albumin (BSA) were collected after 1, 2, and 3 days, pooled, treated to remove residual PHA, precipitated with saturated ammonium sulfate, dialyzed, aliquoted, and stored at -20 degrees C. PHA-SNs stimulated proliferation of homologous lymphoblasts, but not resting splenocytes. SDS-PAGE of metabolically labeled PHA-SNs revealed a band between 14 and 21 kDa. This corresponds to the M(r) of the gel fractions with biological stimulatory activity eluted from PHA-SNs. Blasts absorbed significant bioactivity of PHA-SNs whereas freshly harvested splenocytes did not. Although splenocytes cultured in medium supplemented with 1% fetal bovine serum (FBS) did not proliferate in response to PHA, they did secrete a cytokine with lymphoblast growth-promoting activity. Furthermore, PHA-induced lymphoblasts, initially cultured in medium supplemented with 0.25% BSA, could proliferate in response to PHA-SNs in 1% FBS-supplemented medium.

Ultrastructural and histochemical features of the thymus glands of the adult lungless salamander, Plethodon glutinosus (Caudata: Plethodontidae)

The thymus glands of adult slimy salamanders (Plethodon glutinosus) were examined by light and electron microscopy with the objective of describing the populations of epithelial cells believed to be secretory. The results of various histochemical procedures designed to demonstrate nucleic acids, proteins, lipids, and mucosubstances were evaluated by light microscopy. Each thymus is incompletely subdivided into a variable number of interconnected lobules by trabeculae extending inward from a thin capsule composed of connective tissues. The thymic parenchyma lacks distinct cortical and medullary regions, although developing lymphocytes and plasma cells tend to accumulate in larger numbers in the outermost portions of the glands. Basophils are found regularly in the capsule and trabeculae, but only very rarely within the thymic parenchyma. The epithelial cells of the thymus can be classified into five categories: epithelial reticular cells; three varieties of granulated cells (types I, II, and III), and myoid cells. Epithelial reticular cells form a three-dimensional network which extends throughout all portions of the thymus. Type I and type II granulated cells can be distinguished from one another by various morphological criteria at the ultrastructural level, but only small differences in the composition of their inclusions can be demonstrated histochemically. Both types of granules are composed principally of a proteinaceous material containing an abundance of primary amino and guanidyl groups. In addition, most type I inclusions possess a lipid component that cannot be demonstrated in type II granules. Type III granulated cells possess very small cytoplasmic inclusions resembling those of gastroenteric endocrine cells. Myoid cells contain concentrically arranged myofibrils composed of sarcomeres. In favorably oriented material, small cysts can be identified whose walls are composed of mixtures of type I cells, type II cells, and epithelial reticular cells. Groups of degenerating epithelial cells form lamellated structures corresponding to Hassall's (thymic) corpuscles.

Phylogeny of functional humoral transplantation immunity: comparative studies in amphibians and rodents

Remarkably comparable observations from parallel experiments in salamanders and mice utilizing three related model systems (implant-induced immunomanipulation; passive transfer; and putative B cell suppression) argue directly that functional humoral transplantation immunity is highly developed at the phylogenetic level of Amphibia and that it plays a major role in regulating graft survival in these species (Fig. 4). Although it is still conjectural whether such humoral immunity and weak H-antigens evolved concurrently, the argument that enhancing atibodies evolved exclusively in viviparous species to protect the fetus from potential rejection by the maternal immune system no longer seems tenable (1).