Assays for Escherichia coli heat-labile enterotoxin (LT): Which of the following laboratory techniques are used to demonstrate or quantify LT activity or antigen?

Introduction / Context:
ETEC produces two principal enterotoxins: heat-labile (LT), structurally and functionally similar to cholera toxin, and heat-stable (ST). Detecting LT helps confirm ETEC in clinical and research settings. Several classic bioassays and immunoassays exist for this purpose.

Given Data / Assumptions:

• LT increases intracellular cyclic AMP in target cells.
• Bioassays rely on characteristic cellular responses.
• Immunoassays detect toxin antigen directly with antibodies.

Concept / Approach:
The Y1 mouse adrenal cell assay measures steroidogenesis stimulated by elevated cAMP after LT exposure. Chinese hamster ovary (CHO) cell assays detect LT-induced morphological rounding related to cAMP changes. Enzyme-linked immunosorbent assay (ELISA) uses specific antibodies to detect LT antigen quantitatively or qualitatively in samples, offering higher throughput and specificity.

Step-by-Step Solution:
Recognize LT mechanism: ADP-ribosylation of Gsα → adenylate cyclase activation → cAMP rise.Link mechanism to bioassay readouts (Y1 steroidogenesis, CHO rounding).Acknowledge ELISA as a sensitive antigen detection method.Since all listed tests are valid, select the inclusive option.

Verification / Alternative check:
Modern labs may also use GM1 ganglioside-binding ELISAs and PCR for LT genes (eltAB), which corroborate these classical assays.

Why Other Options Are Wrong:
Each individual option is correct but incomplete alone; the question asks which techniques are used—hence “All of these.”

Common Pitfalls:
Confusing LT (cAMP-mediated) with ST (cGMP-mediated, tested in suckling mouse or T84 cell assays); choose assays appropriate to the toxin.

Final Answer:
All of these