A cell surface marker of thymus‐dependent lymphocytes in Xenopus laevis is identifiable by mouse monoclonal antibody

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Abstract
A mouse monoclonal antibody (mAb), named XT‐1 (IgG2b,λ), was prepared against J strain Xenopus laevis thymocytes. The determinant recognized by this mAb (XT‐1 determinant) was expressed by 92–98% thymocytes and 22–37% splenic lymphocytes from intact J strain frogs and larvae, as analyzed by flow cytofluorometry. The XT‐1 determinant was also expressed by 20–30% peripheral blood lymphocytes and 5–11% bone marrow lymphocytes from adult, and 11–17% liver lymphocytes from larval J strain Xenopus. Early larval thymectomy depleted XT‐1‐positive cells in the spleen to less than 2% of the total lymphocyte population. Double immunofluorescence experiments revealed that XT‐1+ lymphocytes in the spleen are surface IgM−. The strain distribution study on the expression of XT‐1 determinant suggests the allelic polymorphism of the XT‐1 determinant. The surface antigen identified by the present XT‐1 mAb may provide an important marker for lymphocytes in thymus‐dependent lineage in Xenopus.