(A) allelic exclusion

(B) class switching

(C) differential RNA processing

(D) affinity maturation

Immunoglobulins exist as membrane-bound B-cell receptors or secreted antibodies based on post-transcriptional regulation. This SEO article covers Q.72 with the correct answer and all options explained for immunology exams.

Correct Answer

The correct answer is (C) differential RNA processing.

B cells produce heavy chain transcripts with alternative 3′ exons: secreted forms use secretory tail polyadenylation, while membrane forms splice to include transmembrane exons. Naive B cells favor membrane Ig; activated plasma cells switch to secreted Ig via splicing changes.

Option Breakdowns

(A) Allelic exclusion

Allelic exclusion ensures one B cell expresses one heavy/light chain allele, maintaining monospecificity.
Does not control secreted vs membrane forms from the same gene.

(B) Class switching

Class-switch recombination changes constant region (IgM to IgG/IgA), retaining antigen specificity.
All isotypes can produce both membrane and secreted versions.

(C) Differential RNA processing

Alternative splicing/polyadenylation of heavy chain pre-mRNA selects membrane exons (M1/M2) or secretory tail.
Primary mechanism for form switching during B-cell activation.

(D) Affinity maturation

Somatic hypermutation in germinal centers increases antibody affinity via selection.
Affects binding strength, not membrane/secretory fate.