Expression Pattern of the Cortical Immature Thymocyte Specific Antigen JL1 in Thymomas; a New Adjunctive Diagnostic Marker

ABSTRACT

BACKGROUND: JL1 is a novel antigen that has been reported to be expressed exclusively in immature CD4 CD8 double positive T-cells in the thymic cortex. Thymomas are often infiltrated with lymphocytes that are mostly immature T-cells. METHODS: We evaluated 67 cases of surgically resected thymomas and reviewed their histological, surgical, and clinical findings. Representative sections were immunostained using anti-JL1 monoclonal antibody and the immunostaining score was evaluated in each case. RESULTS: JL1 was strongly positive in immature T cells infiltrated in various subtypes of thymomas. The mean value of the immunostaining score was 0 for type A, 0.24 for the A areas of type AB, 2.71 for the B areas of type AB, 3 for type B1, 1.87 for type B2, 0.67 for type B3, and 0.13 for type C. The immunostaining score correlated with the histological subtypes according to the WHO classification, and stages according to the modified Masaoka system. CONCLUSION: JL1 was specifically detected in immature thymocytes in thymomas. Therefore, JL1 immunostaining can be useful for subtyping thymomas. JL1 can also serve as an adjunctive marker to diagnose thymomas in small biopsy specimens.