Detection of Antibodies Secreted from CirculatingMycobacterium tuberculosis-Specific Plasma Cells in the Diagnosis of Pediatric Tuberculosis

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Abstract
Diagnosis of tuberculosis (TB) in children is difficult because symptoms are often nonspecific or absent in infected children, diagnostic specimens are difficult to obtain from younger children, and >50% have negative TB cultures. Thus, there is an urgent need for improved diagnosis of pediatric TB. This study aimed to evaluate the diagnostic value of a new serological method, the ALS (antibodies in lymphocyte supernatant) assay, for the diagnosis of active TB in children with clinically identified TB. The ALS test is based on the concept that antigen-specific plasma cells are present in the circulation only at times of acute infection and not in latency. A cross-sectional study of pediatric patients (age range, 11 to 167 months) who were clinically identified as TB (n= 58) or non-TB (n= 16) patients was conducted, and they were monitored for 6 months. Healthy children (n= 58) were enrolled as controls. Spontaneous release of TB antigen-specific antibodies by in vitro-cultured, unstimulated peripheral blood mononuclear cells was assessed by an enzyme-linked immunosorbent assay usingMycobacterium bovisbacillus Calmette-Guérin (BCG) as the detecting antigen. Of the patients clinically diagnosed with TB, 15% had culture-confirmed TB, 64% were positive for TB by clinically established scoring charts (K. Edwards, P. N. G. Med. J. 30: 169-178, 1987; G. Stegen, K. Jones, and P. Kaplan, Pediatrics 43: 260-263, 1969; and stop TB Partnership, Childhood TB subgroup, World Health Organization, Int. J. Tuberc. Lung Dis. 10: 1091-1097, 2006), and 91% were TB positive by the ALS method. All TB patients had significantly higher BCG-specific ALS titers at enrollment (optical density [OD], 1.06 ± 0.32) than healthy-control children (OD, 0.18 ± 0.06) and non-TB children (OD, 0.21 ± 0.10) (P= 0.001). The ALS titers declined in children with active disease from enrollment through 6 months following anti-TB therapy (P= 0.001). The ALS assay is a novel diagnostic method with potential applications in the diagnosis of pediatric TB and in subsequent monitoring of treatment effectiveness.