SlOO‐positive Histiocytes in T‐Cell‐dependent Area in Human Lymph Nodes Express P‐Glycoprotein

In the present study, we examined P‐glycoprotein (P‐gp)‐expressing cells in human lymph nodes (LN) from patients with reactive lymph adenitis and various malignant lymphomas (ML). MDRl mRNA was detected in all reactive LN and in 8 of 10 ML samples examined hy reverse transcription polymerase chain reaction (RT‐PCR). The signal intensity of the bands was stronger in samples from T‐cell ML LN than in those from LN of reactive lymph adenitis and B‐celt ML. Immunohisto‐chemistry also showed positive reactivity with cellular components in the LN. The P‐gp‐positive cells, detected by UIC2, in reactive lymph adenitis and ML samples were large in size in the T‐cell‐dependent paracortical area in LN. Further, morphological characteristics were similar in UIC2‐positive cells between reactive and ML LN. Double staining with UIC2 and a hematopoietic cell lineage‐specific monoclonal antibody showed that UIC2‐positive cell co‐expressed S‐100, but not other lymphocyte‐ and ML cell‐specific antigens, indicating that these cells correspond to histiocytes in the T‐cell‐dependent paracortical area. Our results show that P‐gp was expressed in histiocytes but not ML cells in LN, and suggest that this molecule may play an important role in the biological function of histiocytes and/or for maintenance of homeostatic levels in T‐cell ML LN.