FIG 3.

ATM deficiency in B cells attenuates MHV68-driven B cell differentiation. B-Cre-positive and -negative mice were either mock treated or infected intranasally with 10⁴ PFU of MHV68. At 16 days postinfection (dpi), splenocytes were harvested and analyzed using flow cytometry. Each data point represents an individual mouse; data from 2 to 4 independent experiments were pooled. (A) Class-switched B cells were pregated on B220⁺ and identified as IgM⁻ IgD⁻ (a representative flow diagram is shown). Boxed areas identify immune populations of interest. (B and C) The frequencies (B) and the absolute numbers (C) of B220⁺ IgM⁻ IgD⁻ splenocytes were quantified. (D) Germinal center B cells were pregated on B220⁺ and further identified as CD95⁺ GL7⁺ (a representative flow diagram is shown). (E and F) Frequencies (E) and absolute numbers (F) of B220⁺ CD95⁺ GL7⁺ splenocytes. (G) Plasma cells were pregated on B220⁺, further gated as IgM⁻ IgD⁻, and identified for surface expression of CD138⁺ and for intracellular IgG⁺ (representative flow diagrams are shown). (H and I) Frequencies (H) and absolute numbers (I) of B220⁺ IgM⁻ IgD⁻ CD138⁺ IgG⁺ plasma cells. (J to M) Serum total immunoglobulin (J) and MHV68-specific antibodies (total [K], IgM [L], and IgG [M]) were measured by ELISA at 16 days post-mock treatment or -MHV68 infection; pooled data are shown. *, P < 0.05; **, P < 0.01; ***, P < 0.001. The error bars indicate standard deviations.