Antigen (labelled, drawn ~20× size)The selected clonePlasma cellsAntibodies; titer traceClonal selection, about 150 µm of a lymph-node follicle at true scale (ruler: 1 tick = 10 µm); the coverslip stands in for the follicle, and the 100 nm antigen particles and antibodies are drawn ~20× size. Every naive B cell carries one receptor, here a key; about one in 10⁵ fits a given antigen. Only that cell is selected: it turns GFP, swells and divides every ~8 h for five days, ~13 divisions and ~10⁴ cells. The field shows 64 places on a log scale of clone size. Some daughters become plasma cells, each secreting ~2,000 antibodies a second; IgM titer peaks near day 11, the clone shrinks to memory cells, and the antigen is cleared. A second dose on day 21 meets those memory cells: IgG rises within days to 10–100× the first peak. Days 0–35 run in 21 s, ~140,000× faster.
~1 in 10⁵能识别某一抗原的初始 B 细胞比例naive B cells that fit a given antigen~6–8 h活化后克隆的分裂周期clone doubling time after activation~2,000/s每个浆细胞分泌的抗体数antibodies secreted per plasma cell~day 10–14初次应答（IgM）峰值primary (IgM) response peak10–100×再次应答（IgG）比初次高secondary (IgG) response vs primary~10¹⁰–10¹¹人体 B 细胞总数B cells in a human body