Mycobacterium tuberculosis (MTB)-stimulated production of nitric oxide by human alveolar macrophages and relationship of nitric oxide production to growth inhibition of MTB.
METHODS
Although nitric oxide (NO) is a major proximate mediator of microbicidal activity in murine macrophages against intracellular pathogens including mycobacteria, its production by and effector role in human macrophages is not clear.


OBJECTIVE
To determine the capacity of Mycobacterium tuberculosis (MTB) to stimulate NO in human monocytes (MN) and alveolar macrophages (AM) and to assess the relationship between NO production and intracellular growth of MTB.


METHODS
NO production (measured as nitrite) by MTB (H37Ra)-infected macrophages and intracellular growth of MTB were measured in cells from 17 healthy subjects.


RESULTS
MTB (5:1, MTB:cells) stimulated little to no NO by MN, but induced NO in AM at days 4 and 7 after infection. There was, however, variability in the response by AM to MTB: among seven subjects MTB-induced NO was low (4 +/- 2 microM, mean +/- SE); six subjects were moderate (56 +/- 11); four subjects were high (502 +/- 167). NO synthase inhibitors inhibited the production of NO by AM but did not significantly affect the intracellular growth of MTB, although a trend towards increased intracellular growth was seen on day 4 of culture. Intracellular growth of MTB in AM from low NO producers was significantly higher than that in AM from moderate NO producers, P < or = 0.05. Inducible NO synthase (iNOS) mRNA by RT-PCR was constitutively expressed by both MN and AM, but was further stimulated by MTB in AM > MN; MTB-induced iNOS protein was present in both MN and AM by Western blot analysis.


CONCLUSIONS
Thus, MTB-infected human AM are capable of producing NO and NO production correlates with intracellular growth inhibition of MTB in AM suggesting that NO may serve either directly or indirectly as a mycobactericidal mediator in human tissue macrophages.
Rich
E A
EA
Department of Medicine, Case Western Reserve University, Cleveland, OH 44106-4984, USA.
Torres
M
M
Sada
E
E
Finegan
C K
CK
Hamilton
B D
BD
Toossi
Z
Z
D000328:Adult; D018929:Cell Culture Techniques; D015169:Colony Count, Microbial; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D016676:Macrophages, Alveolar / Q000378:metabolism* / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000254:growth & development / Q000502:physiology*; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014376:Tuberculosis / Q000378:metabolism*
D004791:Enzyme Inhibitors; D012333:RNA, Messenger; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase