Relationship of PCV to PPE. Mean PCV (± standard error of the mean) of thymectomized calves treated with an isotype-matched MAb (•, control MAb) or anti-CD4 MAb (▾, anti-CD4 MAb) or mean PPE (± standard error of the mean) of thymectomized calves treated with an isotype-matched MAb (○, control MAb) or anti-CD4 MAb (▿, anti-CD4 MAb). The arrows indicate the day of infection for each experiment (experiment 1, day 5 following the commencement of MAb treatment; and experiment 2, day 12 following the commencement of MAb treatment).