# DBT JRF 2020 — Question 36

Exam: DBT JRF 2020 · Section: B · Topic: Bioprocess Engineering · Difficulty: Hard

## Question

Immobilization of enzymes to water insoluble, anionic porous carriers often results in an apparent shift in the pH optima of the enzyme. The physico-chemical interaction likely to cause such a behaviour is

## Options

- **A.** internal mass transfer limitation
- **B.** partitioning effect
- **C.** enzyme deactivation
- **D.** external mass transfer limitation

## Answer

Option B

## Explanation

ELISPOT (Enzyme-Linked ImmunoSpot) assay measures immune responses at the single-cell level. Principle: cells are incubated in wells coated with a capture antibody (e.g. anti-cytokine). Each cytokine-secreting cell creates a localised 'spot' of secreted cytokine directly on the membrane beneath it, captured by the coating antibody. After removing cells, spots are detected with a secondary antibody-enzyme conjugate + substrate, producing a visible precipitate. Each spot = one secreting cell. Advantages: detects even rare cytokine-secreting cells (1/100,000); captures cytokines before dilution or degradation; provides both frequency and secretion level data. This single-cell resolution makes ELISPOT far more sensitive than bulk ELISA for detecting antigen-specific T cells or antibody-secreting B cells.

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