Blocking effect of human T lymphocyte extracts on E-rosette inhibition by sheep red cell fragments

Abstract

Rosette formation, particularly active rosette formation, of human peripheral blood lymphocytes with sheep red blood cells (SRBC) was inhibited by the pretreatment of lymphocytes with sonicated SRBC fragments. However, when SRBC fragments were pretreated with a freeze-thawed extract of unfractionated peripheral blood lymphocytes, the inhibitory activity of SRBC fragments on E-rosette formation was abolished. Based on the different rosetting abilities, peripheral lymphocytes were separated into the populations enriched with active rosette-forming cells, late rosette-forming cells, and non-rosette-forming cells by rosette formation with SRBC followed by gradient centrifugation. A soluble extract of each population was prepared by extensive freeze-thawing in phosphate-buffered saline and the activity of each extract was assayed with the blocking effect on E rosette inhibition by SRBC fragments. This blocking activity was identified in the extract from the population enriched with active rosette-forming cells as well as in the extract from unfractionated peripheral blood lymphocytes, but not in the extracts from the other cell populations. These results suggest that the active rosette-forming cells of human lymphocytes have a unique receptor activity for SRBC fragments, presumably for intact SRBC, and the active materials in this cell population, although dissociated from the cells. retain their ability to bind competitively to SRBC fragments.