इम्यूनोग्लोबुलिन E के बारे में निम्नलिखित में से कौन सा कथन गलत... | Agrigyan

Typical virion diameters in veterinary virology are:

• Poxviruses: Largest animal viruses, brick-shaped, measuring approximately $200\text{--}400\text{ nm} \times 170\text{--}260\text{ nm}$.
• Herpesviruses: Enveloped icosahedral capsids, approximately $150\text{--}200\text{ nm}$.
• Birnaviruses: Non-enveloped icosahedral dsRNA viruses, approximately $60\text{--}70\text{ nm}$.
• Picornaviruses: Among the smallest animal RNA viruses, approximately $25\text{--}30\text{ nm}$.
  Arranged in descending order: Poxvirus ($\gt 200\text{ nm}$) $\gt $ Herpesvirus ($150\text{--}200\text{ nm}$) $\gt $ Birnavirus ($60\text{--}70\text{ nm}$) $\gt $ Picornavirus ($25\text{--}30\text{ nm}$).
  
  Option analysis:
• Correct. Matches the precise descending dimensions from largest to smallest.
• Represents ascending order.
• Incorrect ranking.
• Swaps Birnavirus and Picornavirus.

IgE is monomeric in structure with a sedimentation coefficient of $8\text{S}$, consisting of two light chains and two heavy epsilon ($\varepsilon$) chains containing four constant domains ($C_H1$ through $C_H4$, meaning an extra domain compared to IgG). Each monomeric IgE molecule has only $2$ antigen-binding $F(ab)$ regions. IgM is the only standard pentameric antibody having $10$ $F(ab)$ arms. Thus, statement 4 is completely false and is the correct answer.

Option analysis:

• True. IgE mediates allergic type I reactions and host defense against helminthic parasites.
• True. Epsilon heavy chains contain four constant domains ($C_H1\text{--}C_H4$), one extra domain compared to IgG.
• True. Elevated IgE correlates with atopy and systemic anaphylaxis.
• Incorrect statement (hence correct answer). IgE is a monomer with two $F(ab)$ regions, NOT a pentamer.