Induction of the CD4-8+ suppressor phenotype in CD4+8+ human thymocytes by phorbol myristate acetate

Human thymocytes were separated according to differential agglutination by peanut lectin (PNA). In the fractions obtained, the distribution and quantitative expression of CD antigens was determined by two-color fluorescence flow cytometry. A major population of CD4+8+ and minor populations of CD4+8- and CD4-8+ cells existed in unfractionated thymocytes. Agglutination of human thymocytes by PNA led to a highly effective enrichment of the CD4+8+ phenotype in the PNA+ thymocytes, and left three distinct phenotypes, CD4+8+, CD4+8-, and CD4-8+, in the PNA-thymocytes. After treatment of the CD4+8+ cells in both PNA+ and PNA- fractions for 20 hr with phorbol 12-myristate 13-acetate (PMA), 60%-90% of the cells expressed the CD4-8+ phenotype, whereas the CD4+8+ phenotype was decreased to 1%-3% of the population. In addition, pretreatment of both PNA+ and PNA- thymocytes with PMA induced suppressor activity in these cells, as shown by inhibition of immunoglobulin secretion by pokeweed mitogen (PWM)-stimulated peripheral blood lymphocytes (PBL).