TB Antigens for Assay Development: CFP-10, ESAT-6 and the 16/38 kDa Panel

Updated 2026-09-20

Why CFP-10 and ESAT-6 anchor TB-specific immunoassays, what the 16 and 38 kDa antigens add, and what to specify when you order recombinant TB antigen raw material.

Why these four antigens

CFP-10 and ESAT-6 are encoded within the RD1 region of Mycobacterium tuberculosis and secreted through the same ESX-1 system. RD1 is absent from all BCG vaccine strains and from most environmental mycobacteria, which is precisely why a response to these two antigens is far more likely to reflect TB exposure than exposure to related organisms. The 16 kDa (alpha-crystallin, HspX) and 38 kDa (phosphate-binding protein, PstS1) antigens come from outside RD1 and have a long history as antibody-detection targets, so the practical panel is a pair of RD1 antigens plus two serology targets — available separately or as fusion constructs covering two or three of them in one polypeptide.

Where they are used

Interferon-gamma release assays read T-cell responses to CFP-10 and ESAT-6, and that framework continues to grow: ELISPOT-based formats established the approach, and new detection chemistries keep extending it — a recent example is a CRISPR-driven aptamer fluorescence method reporting ultrasensitive detection of an ESAT6/CFP10 fusion antigen in plasma. Outside T-cell assays, the antigens serve as immunogens for raising antibody pairs, as calibrator and control material, and in serological development where the 16 and 38 kDa targets carry a long track record. The variability literature is worth reading before you optimise: sources of variability in IGRA results are documented and partly traceable to reagent behaviour.

What to specify when you order

Buffer and pH differ across the panel — the RD1 antigens ship in neutral phosphate buffer or Tris at pH 8.0 to 8.5, which matters if your conjugation or coating chemistry is pH-sensitive. Ask for the lot-specific CoA rather than a catalogue purity figure, confirm whether your application needs an endotoxin specification (recombinant E. coli-expressed material is not automatically low-endotoxin), and state your downstream application so the format — single antigen versus fusion construct — can be matched to the assay you are building. All of it is research-use material; if your programme needs a specific regulatory status, raise it before the first order, not after.

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