Secretion of IL-1β, IL-12p40 and TNF in response to strains of M. tuberculosis. Monocytes from 7 donors were infected with strains and co-cultured for 72 hours. The median secretion of IL-1β was significantly reduced by deletion of the 19 kDa gene (p = 0.02). Introduction of the native 19 kDa gene as Δ19::19 restored secretion to wild type levels but the response to Δ19::19NA and Δ19::19NOG remained significantly less when compared to Δ19::19 (p = 0.031 in both cases). No differences existed between strains in their ability to induce the secretion of IL-12p40 or TNF.