Neutrophils are the predominant infected phagocytic cells in the airways of patients with active pulmonary TB.
BACKGROUND
The exact role of neutrophils in the pathogenesis of TB is poorly understood. Recent evidence suggests that neutrophils are not simply scavenging phagocytes in Mycobacterium tuberculosis (Mtb) infection.


METHODS
Three different types of clinical specimens from patients with active pulmonary TB who underwent lung surgery were examined: sputum, BAL fluid, and cavity contents. Differential cell separation and quantification were performed for intracellular and extracellular bacteria, and bacterial length was measured using microscopy.


RESULTS
Neutrophils were more abundant than macrophages in sputum (86.6% +/- 2.2% vs 8.4% +/- 1.3%) and in BAL fluid (78.8% +/- 5.8% vs 11.8% +/- 4.1%). Inside the cavity, lymphocytes (41.3% +/- 11.2%) were the most abundant cell type, followed by neutrophils (38.8% +/- 9.4%) and macrophages (19.5% +/- 7.5%). More intracellular bacilli were found in neutrophils than macrophages in sputum (67.6% +/- 5.6% vs 25.2% +/- 6.5%), in BAL fluid (65.1% +/- 14.4% vs 28.3% +/- 11.6%), and in cavities (61.8% +/- 13.3% vs 23.9% +/- 9.3%). The lengths of Mtb were shortest in cavities (1.9+/- 0.1 microm), followed by in sputum (2.9 +/- 0.1 microm) and in BAL fluid (3.6 +/- 0.2 microm).


CONCLUSIONS
Our results show that neutrophils are the predominant cell types infected with Mtb in patients with TB and that these intracellular bacteria appear to replicate rapidly. These results are consistent with a role for neutrophils in providing a permissive site for a final burst of active replication of the bacilli prior to transmission.
Eum
Seok-Yong
SY
International Tuberculosis Research Center, Division of Immunopathology and Cellular Immunology, 475-1, Gapo, Masan 631-320, Republic of Korea. syeumkr@gmail.com
Kong
Ji-Hye
JH
Hong
Min-Sun
MS
Lee
Ye-Jin
YJ
Kim
Jin-Hee
JH
Hwang
Soo-Hee
SH
Cho
Sang-Nae
SN
Via
Laura E
LE
Barry
Clifton E
CE
D000328:Adult; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology* / Q000382:microbiology; D001999:Bronchoscopy; D002452:Cell Count; D005500:Follow-Up Studies; D006801:Humans; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D009504:Neutrophils / Q000473:pathology*; D010586:Phagocytes; D011379:Prognosis; D013183:Sputum / Q000166:cytology* / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000382:microbiology / Q000473:pathology*; D055815:Young Adult