CD45RO: a marker for BCR-mediated selection

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Germinal center (GC) B-cell survival is minimally influenced by IgH sequence alone.
• End-stage effector B cells exhibit higher mutation frequencies than founder GC B cells.
• Somatic hypermutation and selection are key processes in adaptive immunity.

Purpose of the Study:

• To develop an assay enriching for GC B cells with increasing somatic mutations.
• To investigate the role of CD45RO expression in B-cell selection and mutation frequency.
• To explore the relationship between CD45RO, B-cell activation, and developmental stage.

Main Methods:

• Subdividing CD19(+)IgD(-)CD38(+)CD77(+) centroblasts (CB) and CD19(+)IgD(-)CD38(+)CD77(-) centrocytes (CC) into CD45RO fractions (RO(-), RO(+/-), RO(+)).
• Assessing IgV(H)4 mutation frequency and selection characteristics across RO fractions.
• Analyzing clonally related sequences and cell surface marker expression (CD69, surface Ig).
• Inducing CD45RO expression via B-cell receptor (BCR) crosslinking.

Main Results:

• Mutation frequency in IgV(H)4 transcripts increased with CD45RO expression in centrocytes (CC), but not centroblasts (CB).
• Centrocytes (CC) showed an increase in replacement mutations correlating with CD45RO expression.
• RO-expressing CC and CB populations exhibited increased CD69 expression and were enriched for surface Ig(+) cells.
• BCR crosslinking significantly increased surface CD45RO on tonsillar and GC B cells.

Conclusions:

• CD45RO expression is associated with increased somatic mutations and selection in centrocytes.
• The CD45RO-associated increase in mutations may be linked to BCR-mediated selection or developmental transitions.
• CD45RO serves as a potential indicator of positive selection and ongoing B-cell maturation within germinal centers.