​

Unknown antigens can be detected or measured by a sandwich ELISA, whereas Elispot assays measure the number of cells capable of secreting particular molecules such as cytokines, which are considered antigens.

Which of the following is true for both assays?

Correct option is D

​

Explanation:

Sandwich ELISA

• Used for detecting and quantifying soluble antigens (e.g., proteins, cytokines, hormones).
• Uses two antibodies: a capture antibody bound to a solid surface and a detection antibody that binds to the antigen.
• The reaction produces a soluble colored product in the supernatant, measured via spectrophotometry.

Elispot Assay

• Measures cytokine-secreting cells at the single-cell level.
• Uses an antibody-coated plate where secreted antigens (e.g., cytokines) bind directly to the surface.
• A secondary detection antibody and enzyme-substrate reaction produce insoluble spots on the plate, which can be counted.

Evaluating the Options:

Option 4 (Correct):

• Sandwich ELISA → Soluble reaction product (measured in liquid).
• Elispot → Insoluble reaction product (spots on the plate).

Option 1 (Incorrect):

• Elispot does not produce a soluble reaction product.

Option 2 (Incorrect):

• Sandwich ELISA produces a soluble product, not an insoluble one.

Option 3 (Incorrect):

• Opposite of the correct answer; Elispot produces insoluble products, and sandwich ELISA produces soluble products.