Suher Zada

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.

Ontogeny of hemopoietic and lymphopoietic tissues in the lizard Chalcides ocellatus (Reptilia, Sauna, Scincidae)

The first and major blood‐forming organ to develop in the viviparous lizard Chalcides ocellatus is the yolk sac, which exhibits prominent erythropoietic activity from as early as stage 21 through birth (stage 41). Myeloid cells and megakaryocytes are produced in the yolk sac from stage 23 onward. During lizard embryogenesis hemopoietic activity is also observed in spleen and bone marrow but in neither kidney nor liver. Cells capable of giving rise to lymphocytes both in vivo and in vitro are first found in the thymus at stage 35. Active lymphopolesis in thymus and spleen begins at stages 36 and 39, respectively. In contrast, the gut‐associated lymphoid aggregates are not evident before birth.

THE GUT-ASSOCIATED LYMPHOEPITHELIAL TISSUE (GALT) OF LIZARDS AND SNAKES

ABSTRACT Lizards and snakes possess numerous lymphoid accumulations associated with the entire alimentary tract. Occurrence, number and size of the majority of these gut-associated lymphoid aggregates are markedly influenced by the ambient seasonal conditions. Studies in the lizard, Chalcides ocellatus revealed that the oesophageal lymphoid aggregates are sensitive to the seasonal changes and are significantly reduced in number and size following adult thymectomy while, lymphoid accumulations of small and large intestines are not affected by either seasonal variation or adult thymectomy thus providing circumstancial evidence of lymphoid cell heterogeneity in reptilian GALT. Since spleen and GALT are, beside thymus, the only well-organized lymphoid structures in lizards, and removal of spleen does not drastically impair allograft rejection or humoral reactivity it was assumed that GALT in lizards is an important peripheral lymphoid organ. Experiments of Nature, however, led to expansion of this postulate. The lizards, Agama stellio and Chamaeleon ahamaeleon possess a lymphoid complex indistinguishable from that of other lizards investigated except for the notorious absence of GALT. Agama stellio rejects skin allografts in a manner and tempo absolutely comparable to those recorded in the GALT-rich lizards, Ch. ocellatus and Tarentola annularis. However, while heterologous erythrocytes and serum albumin are excellent antigens for GALT-rich lizards, the GALT-less lizards, A. stellio and Chamaeleon ahamaeleon are unable to produce but a negligible amount of immune antibodies when confronted with various mammalian erythrocytes or human serum albumin over a wide dose range, via the intraperitoneal, intramuscular or subcutaneous routes and whether the antigen is incorporated or not in Freunds adjuvant. Nevertheless, A. stellio possesses small amounts of 2-mercaptoethanol (2-ME) sensitive heterohaemagglutinins, and forms 2-ME sensitive antibodies when stimulated with Salmonella typhimurium. The results infer that GALT of lizards may play a crucial role in humoral immunity i.e. might be a central lymphoid organ equivalent to the avian bursa of Fabricius.

The development of lymphocytes with T- or B- membrane determinants in the lizard embryo

To study the ontogeny of lymphocytes in the lizard, Chalcides ocellatus antisera were raised in rabbits against thymocytes collected from adult lizards (AATS) or from embryos of stages 40 and 41 (AETS), and against serum immunoglobulins (AGGS). AATS recognized in adult lizards a surface membrane antigenic system (TA) specific to thymocytes and thymus-derived (T-) cells in spleen, and a distinct antigenic entity (Tt) found exclusively on intrathymic lymphocytes. After exhaustive absorption with adult thymocytes, AETS defined a further antigen (TE). On the other hand, AGGS combined with the immunoglobulin (Ig) determinants present in the cytoplasm and surface membrane of lizard presumptive B lymphocytes. Immunofluorescence assays during the development of the T and B lineage showed that TA+ and Tt+ thymocytes increased from 35% at stage 37 to 96% at stage 41, and were exported precociously to the embryonic splenic environment. Embryonic thymocytes were shown to totally lack surface Ig, whereas 40-50% of splenocytes carried cytoplasmic and/or surface membrane Ig determinants. The data revealed further the presence of a subset of splenocytes bearing the specific markers of both T and B cells.

Anti-miracidial effect of recombinant glutathione S-transferase 26 and soluble egg antigen on immune responses in murine schistosomiasis mansoni

The anti‐miracidial potential of recombinant Schistosoma mansoni glutathione S‐transferase 26 (rSmGST26) or native crude soluble egg antigens (SEA) was assessed. The associated dynamics of granuloma formation and immune responses were evaluated. Naive C57BL/6 mice were injected intravenously with multiple doses of either SEA (SEA‐group) or rSmGST26 (GST‐group) 7 days before cercarial infection. The immunized groups and the respective controls were sacrificed 6, 8 and 16 weeks postinfection (p.i.). Acceleration of ova destruction and reduction of granuloma diameter were greater in the GST‐group than the SEA‐group, mainly at 8 weeks p.i. However, the amelioration of hepatic pathology and function was more evident in the SEA‐group. Concurrently, serum‐specific IgG1 levels were elevated throughout the course of infection in the immunized groups compared to the infected controls. Initial rise of all splenic cytokines and serum anti‐SEA IgE levels at 6 weeks p.i. was observed, followed by a dramatic drop in the levels of the proinflammatory cytokines IL‐2, IFNγ, IL‐4 and TNF‐α and IgE at 8 weeks of infection. IL‐I0 level was lower at 8 weeks p.i. than at 6 weeks, but was higher in immunized groups than in infected controls. Several responses may be implicated as an outcome of the present immunization protocol, such as increased levels of blocking antibody (IgG1) and IL‐10 with decreased levels of proinflammatory cytokines and IgE.

LYMPHOCYTE STRUCTURAL HETEROGENEITY IN THE LIZARD, CHALCIDES OCELLATUS

Publisher Summary The immune system of birds and mammals consists of lymphocytes with diverse origins, functions, and surface membrane structures. This chapter discusses a study to determine whether lymphocytes of the lizard, Chalcides ocellatus , could be defined by the presence or absence of thymus-derived lymphocyte specific antigen, readily demonstrable surface immunoglobulins and receptor for erythrocyte-antibody complexes. A specific antiserum was raised in rabbits by immunization with thymocytes from lizards, Chalcides ocellatus , and was absorbed repeatedly with lizard erythrocytes, kidney, and liver cells. In complement-dependent cytotoxicity assays, the absorbed anti-thymocyte serum was, at any given dilution, cytotoxic to lizard thymocytes peripheral blood lymphocytes spleen cells and could be titrated to a plateau defining a population of 100% of thymocytes, about 85% of peripheral blood lymphocyte, and 56% of spleen lymphocytes.