Normal CD5+ B lymphocytes are poor stimulators in the autologous mixed lymphocyte reaction (AMLR)

The AMLR is decreased in chronic lymphocytic leukaemia (CLL), which is characterized by a monoclonal expansion of CD5+ B lymphocytes. Since B cells are used to stimulate the AMLR, we investigated the capacity of normal CD5+ B cells to function as stimulators in the AMLR. We isolated B cells from the peripheral blood of normal individuals and fractionated them into subpopulations enriched for CD5+ and CD5- cells, which were used as stimulators in the AMLR. We found that the CD5- B cells were excellent stimulators, whereas stimulation of AMLR by B cells enriched for CD5+ cells resulted in significantly reduced proliferative responses (P < 0.005). This suggests that the reduced AMLR in CLL is due to the predominance of CD5+ B lymphocytes in the stimulating cell population.