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

Abstract

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‐γ, 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_ε exon sequences, suggesting it might be a truncated transcript without v region and might be a human counterpart of the murine germ‐line C_ε transcript.