Q.35 The membrane of mature B cells have
(A) both IgG and IgM
(B) both IgG and IgD
(C) both IgM and IgE
(D) both IgM and IgD
Mature B cells express both IgM and IgD as membrane-bound antigen receptors, enabling antigen recognition before activation and class switching.
Correct Answer
Option (D) both IgM and IgD is correct. Naïve mature B cells co-express membrane IgM (mIgM) and membrane IgD (mIgD) with identical antigen specificity via alternative RNA splicing, forming the B cell receptor (BCR) complex with CD79a/b for signaling.
Option Analysis
(A) Both IgG and IgM: Incorrect
IgG appears after class switch recombination in activated B cells/plasma cells; mature naïve B cells lack surface IgG, expressing only IgM/IgD before antigen-driven differentiation.
(B) Both IgG and IgD: Incorrect
Similar to (A), IgG is not on mature B cell membranes pre-activation; IgD co-exists with IgM, not IgG, in naïve peripheral B lymphocytes.
(C) Both IgM and IgE: Incorrect
IgE production follows class switching from IgM/IgD in response to IL-4/Th2 cytokines; mature B cells do not express surface IgE initially.
(D) Both IgM and IgD: Correct
Mature circulating B cells display both mIgM and mIgD via alternative splicing of VDJ-Cμ/Cδ transcripts, providing dual BCR isotypes for tonic signaling and antigen encounter.
| Option | Immunoglobulins | Expressed on Mature B Cells? | Stage of Expression |
|---|---|---|---|
| (A) | IgG + IgM | No | Post-class switch |
| (B) | IgG + IgD | No | Post-class switch |
| (C) | IgM + IgE | No | IgE after Th2 help |
| (D) | IgM + IgD | Yes | Naïve mature B |
