CYTOKINE MESSENGER-RNA EXPRESSION DURING AN IN-VITRO RESPONSE OF HUMAN B-LYMPHOCYTES - KINETICS OF B-CELL TUMOR-NECROSIS-FACTOR-ALPHA, INTERLEUKIN (IL)6, IL-10, AND TRANSFORMING GROWTH-FACTOR-BETA-1 MESSENGER-RNAS

Expression of mRNA for eight cytokines was analyzed in an in vitro response-proliferation and Ig-secretion - of normal human B lymphocytes. This was made possible by the use of murine thymoma cells as helper cells in conjunction with human T cell supernatant, and the design of human DNA sequence-specific primers for RT-polymerase chain reaction. mRNAs for interleukin (IL)2 and IL-4, but also for IL-1alpha and IL-1beta remained undetectable during the whole culture period in highly purified B cells prepared by a three-step purification protocol. However, tumor necrosis factor alpha and IL-6 mRNAs peaked during days 1-3 after culture start and became undetectable after 5-6 d, shortly before bulk B cell proliferation started to decline. In contrast, transforming growth factor beta1 mRNA, after a progressive increase during the first few days, and IL-10 mRNA, after a peak on days 1-3, remained detectable in immunoglobulin (Ig)-secreting cultures throughout the observation period of 22 d. Clonal analysis on 8-d cultures that had been seeded with single B cells by autocloning with the cell sorter, revealed that 85% of 77 B cell clones studied, expressed TGF-beta1 mRNA, and only 19% IL-10 mRNA. These findings show a differentiation stage-related cytokine program during a B cell response, whereby (a) B cells can become activated without IL-1alpha or IL-1beta expression; (b) mRNA for positive (IL-10) and negative (TGF-beta1) autoregulatory factors coexists in cell populations during the later phase of the response, although not necessarily in all B cell clones; and (c) normal Ig-secreting cells cease IL-6 expression in contrast to their malignant counterparts, myeloma cells.