N. Badir

Differential effect of seasonal variation on lymphoid tissue of the lizard, Chalcides ocellatus

Abstract In the lizard, Chalcides ocellatus , the thymus and spleen are similar to those of mammals except that lymphoid tissue of the lizards thymus and spleen is atrophic in winter. Lizards also possess numerous dense lymphoid nodules associated with the entire gut mucosa and the submucosa of the ileo-colon junction and the caecum. A peculiar lymphoepithelial macroorgan, resembling the bursa of Fabricius occurs in the colon. Oesophageal nodules are few in winter, but their number and size increase in spring and summer and then decrease in autumn. In contrast, lymphoid tissue of the stomach, small and large intestines does not appear to be affected by seasonal variation. Dichotomy of lymphocyte populations in lizards is suggested.

Lymphoid tissues of the snake, Spalerosophis diadema, in the different seasons.

Abstract The thymus in the snake, Spalerosophis diadema , is lymphoepithelial, clearly differentiated into cortex and medulla; it undergoes involution in both winter and summer. During these seasons, the spleen is divided into distinct white and red pulps. In spring and autumn, lymphocytes completely obscure the splenic stroma so that red and white pulp boundaries are obliterated. Gut-associated lymphoid tissue (GALT) is extensively distributed along the entire gastrointestinal tract. Structures resembling Peyers patches, except in being composed of only two adjacent lymphoid accumulations, are prominent in the small intestine in winter and autumn, while decrease remarkably in number and size in spring and summer (the breeding season). In contrast, the gut-associated aggregates are numerous throughout the year. Differential sensitivity to seasonal variation is suggested as a possible marker for functional lymphocyte populations in reptiles.

Effect of seasonal variation on lymphoid tissues of the lizards, Mabuya quinquetaeniata licht. and Uromastyx aegyptia forsk

The thymus in the lizards Mabuya quinquetaeniata and Uromastyx aegyptia is highly involuted in winter but exhibits in the other seasons a rich lymphoepithelial organization. The splenic white pulp is severely depleted in winter but is extensively developed in spring, summer and autumn. In these seasons, the splenic lymphoid tissue of Mabuya occurs in a continuous phase throughout the organ obscuring the red pulp, whereas in Uromastyx the white pulp remains localized as periarteriolar aggregates and the red pulp is always clearly delineated. In both lizard species, gut-associated lymphoid tissue is well represented, especially in the large intestines and in Mabuya it is almost similar in different seasons. In Uromastyx, in winter, lymphoid nodules are only found in the caecum and the colon, but during warm seasons, inumerable nodules are distributed throughout the gut. The findings are important for a clearer understanding of immunologic competence in reptiles.

SEASONAL DISTRIBUTION AND HORMONAL MODULATION OF REPTILIAN T CELLS

Using PNA and anti-Thy-1 fluorescent binding assays, T lymphocytes of the lizard, Chalcides ocellatus were phenotypically distinguishable into four subpopulations (PNA+ Thy-1-, PNA+ Thy-1+, PNA- Thy-1+ and PNA-Thy-1-), which seemed to be affected independently by endogenous steroid levels. Indeed, the size of PNA+ thymocytes is maximal and coincides with the low level of circulating cortisol during spring through summer and decreases gradually with the elevation of the cortisol level. On the other hand, as the endogenous testosterone (TS) level begins its physiological rise, lympholysis of Thy-1+ thymic cells begins in spring with gradual increase in size and with the decrease in TS levels. Among splenocytes and bone marrow lymphocytes, seasonal-dependent alterations in the size of both lymphocyte subpopulations seemed to correlate in part with the status of the thymus. Direct support of this observation was derived from subsequent in vitro studies with exogenous hydrocortisone (HC) and testosterone propionate (TP) treatments in spring and autumn. In all incidents, the data were indicative of the selective susceptibility of the PNA+ Thy-1- subpopulation to HC in the thymus and not in the periphery, and the susceptibility of the PNA- Thy-1+ subpopulation to TP in all three lymphoid organs tested. In vivo studies with a purified fraction of thymosin alpha 1 (T alpha 1) suggested that the PNA+ Thy-1- subpopulation in the different organs was the selective target for the action of T alpha 1. Finally, the dual treatment with T alpha 1 in vivo followed by TP or HC in vitro confirmed that TP-sensitivity was confined to the PNA- Thy-1+ and HC to PNA(+)-Thy-1- subpopulations in any of the three lymphoid organs.

Effect of hydrocortisone on immune system of the lizard, Chalcides ocellatus. I. Response of lymphoid tissues and cells to in vivo and in vitro hydrocortisone.

A single dose of 1 mg/g body weight of hydrocortisone acetate (HC) administered intraperitoneally to adult lizards, Chalcides ocellatus induced rapidly a reduction of about 85% of thymic lymphocytes. Histological evidence indicated that cortical, as well as, medullary thymocytes are sensitive to HC exposure. Around 40-50% of lymphocytes in peripheral blood (PB) and spleen were depleted at 3-7 days post-HC injection; such depletion durated about 4 weeks for PB but was rather temporary in spleen. Increase in number of bone marrow (BM) lymphocytes was negligible and transient and could by no way account for the dramatic cell losses in the different lymphoid tissues. The findings thus suggested that HC-mediated lymphocyte depletion in lizards is not attributable to redistribution between the different lymphoid compartments but rather to destruction. In direct conformation, lymphocytes were readily lysed in vitro by 10(-3)M HC, thymocytes being more vulnerable greater than PB greater than spleen greater than BM lymphocytes.

Effect of hydrocortisone on immune system of the lizard, Chalcidesocellatus II. Differential action on T and B lymphocytes

Lymphocytes of thymus, spleen, peripheral blood (PB) and bone marrow (BM) collected from adult lizards, Chalcides ocellatus were cultured for 24 hr in the presence of 10(-3)M hydrocortisone acetate (HC) in order to assess the effect of in vitro HC on lizard T and B cell viability. The results indicated that HC induced stepwise, time-dependent mortality of the majority of thymocytes carrying T cell specific antigen(s) (TSA), 30-50% of T cells of spleen, PB and BM, and of a proportion of splenic B lymphocytes. Administration of 1 mg/g body weight HC to adult Ch. ocellatus lead to depletion of all TSA+ thymocytes. In contrast, T lymphocytes in the peripheral lymphoid compartments revealed both sensitivity and resistance to HC; similarly, B lymphocytes constituted susceptible and resistant subpopulations.

Effect of splenectomy on the humoral immune response in the lizard,Scincus scincus

Adult splenectomy in the lizard,Scincus scincus, did not affect humoral immune response to rat erythrocytes until 30 days post-immunization, but severely depressed subsequent antibody production.

SURFACE MARKERS OF LYMPHOCYTES OF THE SNAKE, SPALEROSOPHIS DIADEMA: II. Distribution of snake lymphocyte subpopulations in different seasons

Publisher Summary This chapter discusses studies conducted to examine the distribution of the surface markers of lymphocytes of the snake, Spalerosophis diadema, in different seasons. In indirect immunofluorescent assay, a distinct population of about 29% of splenocytes and 10–15% of peripheral blood lymphocytes was scored as Ig-bearing population in spring and autumn. At any time throughout the year, no Ig-bearing lymphocytes were detected in thymus, with either lower or higher dilutions of the anti-snake γ globulin antiserum. During early summer, when the snake presumably appeared to be structurally thymectomized, the Ig-bearing lymphocytes were represented by 100% of the viable lymphocytes in spleen. The persistence of Ig-bearing lymphocytes in spleen, during this time, with the entire absence of viable thymocytes and thymus-derived lymphocytes in the peripheral lymphoid organs strongly suggests that this population in its sensitivity to seasonal fluctuations is quite different with respect to thymocytes and thymus-derived lymphocytes. The complete absence of Ig-bearing lymphocytes in the thymus at any time throughout the year implies that the Ig-bearing population is totally independent of thymus for its appearance and establishment in the peripheral lymphoid organs and circulation.

Natural heterohaemagglutinins in the serum of the lizard, Agama stellio.

Normal serum from the lizard, Agama stellio, contains a variety of haemagglutinins specific for human, rat and mouse erythrocytes. These natural heterohaemagglutinins are not obviously inhibited by simple sugars, do not require calcium ions for their activity and can act as haemolysins in a specific, complement-dependent manner. They are, moreover, sensitive to 2-mercaptoethanol treatment and can be eluted from the γ-globulin region on cellulose acetate electrophoresis. These results suggest that natural heterohaemagglutinins of A. stellio (Reptilia) have properties similar to those of natural antibodies of advanced vertebrates (birds and mammals).