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.