Differential tumor necrosis factor alpha expression by astrocytes from experimental allergic encephalomyelitis-susceptible and -resistant rat strains

When comparing TNF-ci mRNA and protein expression in the two strains, the differences in TNF-ci mRNA levels are not as striking as those for TNF-a protein, especially in response to either LPS alone or IFN-y/LPS. There are several explanations for these findings, one being the sensitivity of RTPCR . Using conventional Northern blot analysis, we were unable to detect mRNA from LPS-stimulated astrocytes from outbred rat strains (11) , as well as Lewis and BN rats. The analysis by PCR has increased our level of sensitivity, and we are now able to detect TNF-a mRNA from LPS-stimulated astrorytes. It is also possible that the TNF-a gene is effectively transcribed in Lewis and BN astrocytes in response to all the stimuli tested, but there are differences in mRNA stability. We have observed that although TNF-a protein levels are comparable for astrocytes stimulated with IFN-y/LPS and IFN-y/IW0 from Lewis and Sprague Dawley strains (11) , RNA levels are consistently higher from IFNy/IIT1f-stimulated astrocytes. This may reflect TNF-(x mRNA instability in LPS-stimulated astrocytes, as observed by Lieberman et al . (10) . Alternatively, transcriptional activity in response to LPS for Lewis astrocytes, and IFN-y/II710 for BN astrocytes, may occur, with a subsequent block in either translation or secretion of mature TNF protein .