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Identification of human macrophage genes differentially expressed by infection with Mycobacterium tuberculosis Tang, Raymond Kwok-Cheung


Mycobacterium tuberculosis infects mononuclear phagocytes and manifests disease by triggering a strong delayed type hypersensitivity response which is detrimental to the host. In most healthy individuals, infection is resolved; however, the bacillus possesses many evasion strategies which may allow it under certain conditions to survive and replicate within the macrophage. M. tuberculosis has been found to alter several host defences to promote its survival so the ability of M. tuberculosis to modulate the expression of genes in human macrophages was investigated, using a novel method which combined subtractive hybridization with differential display. Macrophage genes which appeared to be induced or suppressed by infection were identified and isolated. A total of 25 such cDNAs were isolated. Five of the cDNAs were identified as known genes: NADH ubiquinone oxidoreductase chain 2; p22-phox; an antioxidant enzyme, AOE 37-2; a possible growth arrest gene, B4B; and a human protein phosphatase g. Seven other cDNAs matched human cDNA sequences, and the remaining 13 were novel sequences. Successful quantitation of three cDNAs revealed that two were induced in macrophages infected with M. tuberculosis, while the other was constitutively expressed. In addition, three other cDNAs were also identified to be induced by infection. The sequence of one of the cDNAs matched an IFNinducible nuclear phosphoprotein sequence, another matched a cDNA sequence, while the last one was unique. These cDNAs were clearly induced by infection in THP-1 macrophages; however, a pattern of expression of these clones did not emerge in human peripheral blood macrophages. Further research must be performed before conclusions can be made regarding the expression and function of these clones.

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