T cell response to alpha crystallin and Mycobacterium tuberculosis specific antigens using ex-vivo elispot assay for detecting latent tuberculosis infection in Addis Ababa, Ethiopia.

BACKGROUND: Mycobacterium tuberculosis (Mtb) persists in a state of non-replication or stationary phase, but resulting in active tuberculosis (TB) when the immune system is suppressed. Alpha-crystallin (ACR) is one of the bacterial antigens characterized known to be related to shifting of the bacilli from growth to a non-replicating persistent state.

OBJECTIVE: To compare the ex-vivo responsiveness of active TB patients, close household contacts and healthy controls to specific Mtb antigens.

METHODOLOGY: Antigen-specific interferon-gamma (IFN-g) responses were measured to a 16kDa-alpha crystallin (ACR) antigen along with its peptides and other Mtb antigens (ESAT-6, CFP-10, PPD, TB10.3 and Ag85A) in 39 active TB patients, 23 close household contacts and 25 community controls, using ex-vivo ELISPOT RESULT: The proportion of responders to ACR was 36% in active TB patients (76 +/- 14 spot forming cells), 48% in close household contacts (123 +/- 31 spot forming cells) and 76% in community controls (165 +/- 29 spot forming cells) indicating the presence of latency more in the community controls compared to the other groups. Sixty percent of community controls (131 +/- 27 spot forming cells), 61% of healthy household contacts (138 +/- 3 spot forming cells) and 54% of TB patients (198 +/- 37 spot forming cells) showed ESAT-6-specific T cell responses.

CONCLUSION: Antigen specific T cell response based on ex-vivo ELISPOT assay using combined ACR and ESAT-6/ CFP-10 antigens can be used as indicator of underlying latent TB infection in tropical setting where tuberculosis is endemic.