Identification of immunogenic Salmonella enterica serotype Typhi antigens expressed in chronic biliary carriers of S. Typhi in Kathmandu, Nepal.
BACKGROUND
Salmonella enterica serotype Typhi can colonize and persist in the biliary tract of infected individuals, resulting in a state of asymptomatic chronic carriage. Chronic carriers may act as persistent reservoirs of infection within a community and may introduce infection to susceptible individuals and new communities. Little is known about the interaction between the host and pathogen in the biliary tract of chronic carriers, and there is currently no reliable diagnostic assay to identify asymptomatic S. Typhi carriage.


RESULTS
To study host-pathogen interactions in the biliary tract during S. Typhi carriage, we applied an immunoscreening technique called in vivo-induced antigen technology (IVIAT), to identify potential biomarkers unique to carriers. IVIAT identifies humorally immunogenic bacterial antigens expressed uniquely in the in vivo environment, and we hypothesized that S. Typhi surviving in the biliary tract of humans may express a distinct antigenic profile. Thirteen S. Typhi antigens that were immunoreactive in carriers, but not in healthy individuals from a typhoid endemic area, were identified. The identified antigens included a number of putative membrane proteins, lipoproteins, and hemolysin-related proteins. YncE (STY1479), an uncharacterized protein with an ATP-binding motif, gave prominent responses in our screen. The response to YncE in patients whose biliary tract contained S. Typhi was compared to responses in patients whose biliary tract did not contain S. Typhi, patients with acute typhoid fever, and healthy controls residing in a typhoid endemic area. Seven of 10 (70%) chronic carriers, 0 of 8 bile culture-negative controls (0%), 0 of 8 healthy Bangladeshis (0%), and 1 of 8 (12.5%) Bangladeshis with acute typhoid fever had detectable anti-YncE IgG in blood. IgA responses were also present.


CONCLUSIONS
Further evaluation of YncE and other antigens identified by IVIAT could lead to the development of improved diagnostic assays to identify asymptomatic S. Typhi carriers.
Division of Infectious Diseases, Massachusetts General Hospital, Boston, Massachusetts, USA. rccharles@partners.org
Richelle C
RC
Charles
Tania
T
Sultana
Mohammad Murshid
MM
Alam
Yanan
Y
Yu
Ying
Y
Wu-Freeman
Meagan Kelly
MK
Bufano
Sean M
SM
Rollins
Lillian
L
Tsai
Jason B
JB
Harris
Regina C
RC
LaRocque
Daniel T
DT
Leung
W Abdullah
WA
Brooks
Tran Vu Thieu
TV
Nga
Sabina
S
Dongol
Buddha
B
Basnyat
Stephen B
SB
Calderwood
Jeremy
J
Farrar
Farhana
F
Khanam
John S
JS
Gunn
Firdausi
F
Qadri
Stephen
S
Baker
Edward T
ET
Ryan
D000328:Adult; D000942:Antigens, Bacterial / Q000032:analysis* / Q000276:immunology; D001659:Biliary Tract / Q000382:microbiology*; D002353:Carrier State / Q000382:microbiology*; D002648:Child; D002675:Child, Preschool; D020869:Gene Expression Profiling; D054884:Host-Pathogen Interactions; D006801:Humans; D009390:Nepal; D012485:Salmonella typhi / Q000276:immunology*; D014435:Typhoid Fever / Q000382:microbiology*
D000942:Antigens, Bacterial