CHARACTERIZATION OF A HIGH-MOLECULAR-WEIGHT TUMOR-NECROSIS-FACTOR-ALPHA MESSENGER-RNA IN INFLUENZA-A VIRUS-INFECTED MACROPHAGES

Infection by influenza A virus has previously been shown to prime macr ophages for a high TNF-alpha production. Influenza A virus induced a T NF-alpha mRNA accumulation that consisted of two types: a regular 1.7 kb and an additional high m.w. 2.4 kb species in murine macrophages, a nd a high m.w. 3.6 kb species in human monocytes. In this study, we fu rther characterized this virus-induced, novel high m.w. TNF-alpha mRNA . The additional high m.w. TNF-alpha mRNA represented a true polyadeny lated mRNA and its induction required exposure to infectious viruses. The regular and the high m.w. TNF-alpha mRNA were both found in the nu clear fraction and the cytoplasm. We excluded that the novel high m.w. TNF-alpha mRNA was an intron-containing precursor TNF-alpha mRNA that could have persisted in virus-infected macrophages. When TNF-alpha ex ons 1 to 4 and TNF-alpha exons 2 to 4 were amplified by polymerase cha in reaction, only regular and no high m.w. bands were detected. By use of specific TNF-alpha intron I and intron III cDNA we could definitel y demonstrate the absence of introns in the high m.w. TNF-alpha mRNA. The high m.w. TNF-alpha mRNA was free of TNF-beta and TNF intergenic r egion elements but contained the 5' and 3' untranslated region of TNF- alpha. Influenza A virus infection also induced a double band of IL-1b eta and IL-6 mRNA. Whether this novel high m.w. TNF-alpha mRNA represe nts a virus-induced abnormality or a superinduction of an otherwise no rmal but minor TNF-alpha transcript, and whether this high m.w. TNF-al pha mRNA species codes for a biologically active product, remains to b e examined.