70-75 kd molecules expressed on LGL and T cells recognized by a mitogenic monoclonal antibody YTA-1; co-modulation and functional association with the interleukin 2 receptor p75.

We have raised a mAb YTA-1 which recognizes 75 kd antigen (Ag) on large granular lymphocytes (LGL) and T cells using a human natural killer (NK)/LGL cell line YT as the immunogen. YTA-1 mAb not only enhanced the growth of peripheral blood mononuclear cells (PBMC) but also down-regulated both high- and intermediate-affinity interleukin 2 receptors (IL-2R) on resting PBMC. When incubated with 5-50 micrograms/ml of YTA-1 mAb at 37 degrees C, up to 50% of high- and intermediate-affinity IL-2R of the Tac+ YT subclone (YTCl.1) were down-regulated within 120 min. YTA-1 mAb also down-regulated the intermediate-affinity IL-2R on YT2C2 cells, which express only IL-2Rp75. On the other hand, 5 nM recombinant IL-2 down-regulated the expression of YTA-1 Ag on YT cells after 120 min culture, indicating a close association between YTA-1 Ag and IL-2R. However, YTA-1 mAb did not affect the low-affinity IL-2R on an HTLV-1+ T cell line MT-1. Furthermore, interleukin 1 receptor (IL-1R) on YT cells was not affected by YTA-1 mAb. It appears that the down-regulation by YTA-1 mAb is selective for IL-2Rp75 of the IL-2R complex. Pre-incubation of YT cells with 20 micrograms/ml YTA-1 mAb accelerated the internalization of IL-2Rp75 but did not accelerate that of IL-2Rp55, indicating that YTA-1-induced down-regulation of IL-2R is associated with the internalization of IL-2Rp75.(ABSTRACT TRUNCATED AT 250 WORDS)