β₂AR stimulation induces lymphopenia in a cell-intrinsic manner. (A and B) Numbers of B cells (CD19⁺, top) and CD4⁺ T cells (CD4⁺, bottom) in blood (A) and lymph (B) that were collected from WT mice 2 h after i.v. injection with the indicated doses of clenbuterol or salbutamol. Data are pooled from seven experiments and are shown as mean ± SEM for at least three mice. (C and D) Numbers of B cells (top) and CD4⁺ T cells (bottom) in blood (C) and lymph (D) at the indicated times after i.v. injection of saline, clenbuterol (0.4 mg/kg), or salbutamol (12 mg/kg). Data are pooled from 11 experiments and are shown as mean ± SEM for at least five mice. (E) Quantitative RT-PCR analysis showing the abundance of Adrb2 mRNA transcripts (encoding β₂AR) relative to Gapdh (encoding glyceraldehyde-3-phosphate dehydrogenase) for the indicated lymphocyte populations isolated from the mouse spleen. Data are representative of three experiments and shown as mean + SD of triplicates. (F and G) B cell numbers in blood (F) and lymph (G) from WT (Adrb2^+/+ or Adrb2^+/− littermates) or Adrb2^−/− mice that received i.v. injection of saline or clenbuterol (0.4 mg/kg). Data are pooled from five experiments. (H and I) BM chimeras generated using WT or Adrb2^−/− (−/−) mice as donors and recipients received i.v. injection of saline or clenbuterol (0.4 mg/kg), and 2 h later, the fractions of B cells in the blood (H) and lymph (I) were determined as percentages relative to those in saline-treated mice. Data are pooled from six experiments and the dashed lines show the levels of saline-treated control as 100%. Each symbol represents an individual mouse and bars indicate means (F–I). Sal, Saline; Clen, clenbuterol; Salb, salbutamol. *, P < 0.05; **, P < 0.01; ****, P < 0.0001; ns, not significant (one-way ANOVA with Bonferroni’s post-test).