Cultures of the murine myelomonocytic cell line, WEHI-3, can be induced to express the Class II MHC antigen, I-A, by incubation with rMuIFN-gamma and/or rHuTNF-alpha. A 24-hr incubation with the combination of rMuIFN-gamma (5.6 ng/ml) and rHuTNF-alpha (13 ng/ml) induced the highest level of expression in the cell population (more than 90%), followed by rMuIFN-gamma (75%) and rHuTNF-alpha (33%). Comparison of the level of mRNA for the heavy chain subunit of the I-A molecule, A alpha, indicates that the combination is 10 and 40 times as stimulatory as rMuIFN-gamma and rHuTNF-alpha alone, respectively. Each cytokine treatment induced a time-dependent increase in the level of A alpha mRNA over the 72 hr of incubation examined, although the combination continued to elevate the level of A alpha mRNA above that induced by either cytokine alone. The findings reported here demonstrate that the monokine rHuTNF-alpha can induce I-A antigen expression and A alpha mRNA. Furthermore, stimulation by the combination of rHuTNF-alpha and rMuIFN-gamma is more than additive, relative to the effects of each cytokine as individual agents.
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Chang et al. (1986) studied this question.