Human IgE mRNA expression by peripheral blood lymphocytes stimulated with interleukin 4 and pokeweed mitogen.

Expression of human IgE mRNA by peripheral blood lymphocytes (PBL) and an IgE-producing myeloma cell line, U-266, was examined by Northern blot hybridization and compared with IgE levels in culture supernatants. A 2.35-kb IgE mRNA was detected in unstimulated atopic PBL and U-266 cells but not in normal PBL, and its levels correlated with IgE protein levels in the supernatant. Upon stimulation with interleukin 4, a new 1.75-kb transcript was revealed in both atopic and normal PBL but not in U-266 cells. Its expression did not correlate with IgE levels in the supernatant. Pokeweed mitogen also induced the expression of the 1.75-kb transcript without concomitant induction of IgE synthesis by normal PBL and even suppressed the spontaneous expression of the 2.35-kb transcript and IgE protein synthesis by atopic PBL. Interferon-gamma, which suppressed both the 2.35-kb transcript and IgE protein production, had no inhibitory effect on the 1.75-kb transcript. Expression of the 1.75-kb transcript was already high after 2 days of stimulation and peaked around day 4. The length of the transcript is smaller than that of mRNA coding for secreted human IgG and IgA and contains all four C epsilon exon sequences, suggesting it might be a truncated transcript without v region and might be a human counterpart of the murine germ-line C epsilon transcript.