Matrix metalloproteinase‐9 (MMP‐9) activity is implicated in pathogenesis of central nervous system tuberculosis (CNS‐TB). IFNγ, a key cytokine in TB, usually inhibits MMP‐9 secretion. Addition of IFNγ to conditioned media from M. tb‐infected monocytes (CoMTB) resulted in a 7‐fold increase in MMP‐9 activity detected by gelatin zymography (P<0.01). In contrast, tissue inhibitor of metalloproteinase (TIMP)‐1 and ‐2 secretion, measured by ELISA, was suppressed. Dexamethasone abolished the synergistic increase in MMP‐9 activity. Interleukin (IL)‐1β in CoMTB is a critical mediator of synergy with IFNγ, and IL‐1β alone synergizes with IFNγ to increase MMP‐9 secretion from 51 ± 31 to 762 ± 136 U. IL‐1β activity is dependent on p38 mitogen‐activated protein (MAPK) kinase, which was found to be phosphorylated in tissue specimens from patients with CNS‐TB. Extracellular signal regulated kinase (Erk) and p38 MAPK activation did not affect IFNγ signaling pathways. Inhibition of janusactivated kinase (JAK)‐2 by 50 μM AG540 decreased MMP‐9 secretion to 124 ± 11.1 from 651 ± 229 U of activity (P<0.01). However, signal transducer and activator of transcription (STAT)‐3 but not STAT‐1 phosphorylation was synergistically up‐regulated by IFNγ and CoMTB. In summary, synergy between IL‐1β and STAT‐3 dependent IFNγ signaling is key in control of up‐regulation of MMP‐9 activity in CNS‐TB and may be a significant mechanism of brain tissue destruction.—Harris, J. E., Fernandez‐Vilaseca, M., Elkington, P. T. G., Horncastle, D. E., Graeber, M. B., and Friedland, J. S. IFNα synergizes with IL‐1β to upregulate MMP‐9 secretion in a cellular model of central nervous system tuberculosis. FASEB J. 21, 356–365 (2007)