Q.9 Heat inactivation of serum is done to inactivate
(A) prions (B) mycoplasma (C) complement (D) pathogenic bacteria
Heat inactivation of serum at 56°C for 30 minutes primarily inactivates complement proteins to prevent cell lysis in culture, making (C) the correct answer. This standard lab protocol ensures serum compatibility with sensitive mammalian cells.
Correct Answer
The correct option is (C) complement. Complement cascade proteins (C1-C9) in serum can lyse nucleated cells via membrane attack complex formation during culture. Heating denatures heat-labile components (C1, C2, C4) while preserving growth factors, essential for immunology assays and primary cell lines.
Option Explanations
FBS/serum heat inactivation targets thermolabile immune effectors; protocol timing/temperature critical to avoid protein precipitation.
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(A) Prions: Incorrect; prions resist 56°C/30min (require autoclaving/NaOH); heat inactivation ineffective against misfolded PrPSc.
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(B) Mycoplasma: Incorrect; mycoplasma survive heat (need filtration/antibiotics); common contaminants reduced by 0.1μm sterile filtration.
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(C) Complement: Correct; destroys classical/alternative pathway initiators, preventing cytotoxicity in lymphocyte/ESC cultures.
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(D) Pathogenic bacteria: Partially true (kills vegetative bacteria) but unnecessary; gamma irradiation/0.1μm filtration standard for sterility.
Mechanism Overview
Serum water bath at 56°C ± 0.5°C for 30min, swirl periodically, ice quench. Complement C3-C9 partially remain but nonfunctional without initiators. Risk: excess heat (>60°C) denatures labile vitamins/growth factors. Modern low-complement FBS reduces need except for complement-sensitive applications.
| Target | Heat Sensitivity | Inactivated by 56°C/30min? |
|---|---|---|
| Complement | High | Yes |
| Mycoplasma | Low | No |
| Prions | Very low | No |
| Bacteria | Variable | Partial |
