TARC, a CC chemokine, is frequently expressed in classic Hodgkin's lymphoma but not in NLP Hodgkin's lymphoma, T-cell-rich B-cell lymphoma, and most cases of anaplastic large cell lymphoma

Thymus and activation-regulated chemokine (TARC) has been identified as a l ymphocyte-directed CC chemokine that attracts activated T-helper type 2 (Th 2) cells in humans. Recent studies showed that the T cells surrounding Reed -Sternberg cells in Hodgkin's lymphomas (HL) are Th2 type. Anaplastic large cell lymphomas (ALCL), T-cell-rich B-cell lymphoma (TCRBCL) can mimic HL i n some instances. This study aimed to establish the pattern of TARC express ion in these diseases. Immunohistochemical stain using a polyclonal goat an ti-human antibody to TARC was performed on 119 cases of confirmed HL; 99 we re classical type (43 mixed cellularity, 43 nodular sclerosis, 5 lymphocyte depleted, 4 lymphocyte rich, 4 unclassifiable) and 20 lymphocyte predomina nt HL. Additional 27 ALCL (9 T-, 18 null-cell phenotype), 16 T-cell and 8 B -cell non-Hodgkin's lymphoma (NHL) were studied. A total of 85.8% of the cl assical HL, one case of ALCL, and one case of large cell B-cell lymphoma wi th anaplastic morphology showed positive TARC expression in the tumor cells . The expression was paranuclear and/or diffuse in the cell cytoplasm. The tumor cells in all cases of lymphocyte predominant HL, TCRBCL, null ALCL, a nd T-NHL did not express TARC. The high frequency of TARC expression in the Reed-Sternberg cells of classical HL may explain the characteristic T-cell infiltrate in this disease. The absence in other types that may be morphol ogically similar indicates that staining for TARC may aid in differential d iagnosis.