Immunology recall – heat sensitivity of antibody classes: Among the major human immunoglobulin (antibody) classes, which one is characteristically heat-labile (readily inactivated by moderate heating such as 56 °C for standard laboratory treatment)?

Introduction / Context:
Understanding the thermal stability of antibody classes is important in immunodiagnostics and allergy testing. Laboratories routinely heat sera (for example, at 56 °C) to inactivate complement; however, different immunoglobulin isotypes tolerate heat differently. This question tests recognition of the antibody class that is notably heat-labile.

Given Data / Assumptions:

• Sera may be heated during sample preparation (e.g., complement inactivation).
• Antibody isotypes have distinct structures (monomeric vs polymeric) influencing stability.
• We compare common human isotypes: IgG, IgA, IgM, and IgE.

Concept / Approach:
IgE is structurally similar in basic domain architecture to IgG but is markedly more labile to heat and storage, which matters for assays that measure IgE (e.g., total IgE or allergen-specific IgE). In contrast, IgG is relatively heat-stable under complement-inactivation conditions; polymeric IgM is large and can lose activity with heat but is not classically labeled the most heat-labile; secretory IgA is protected by the secretory component in mucosa but serum IgA overall tolerates routine handling better than IgE.

Step-by-Step Solution:
Identify which isotype is classically described as heat-labile in clinical immunology. Recall that IgE levels can drop with routine heat treatment, affecting allergy assays. Therefore, select IgE as the best answer.

Verification / Alternative check:
Laboratory guidelines caution against heating samples for IgE assays because activity and epitope recognition decline after moderate heating, confirming practical heat lability.

Why Other Options Are Wrong:
IgG is comparatively heat-stable at 56 °C for short periods; IgA and IgM can be affected but are not the most labile in routine workflows.

Common Pitfalls:
Confusing heat inactivation of complement (a serum component) with heat sensitivity of the antibodies themselves; not all isotypes respond the same.

Final Answer:
IgE.