Kinetics of phytohemagglutinin response in chickens infected with various strains of Marek's disease virus.

Phytohemagglutinin (PHA) response of whole blood lymphocytes from white leghorn inbred line 7(2) chickens infected with various strains of Marek's disease virus (MDV) was monitored sequentially for 6 weeks postinfection. A significant difference between JM and GA strains was shown. A two-phase depression in the PHA response was observed in chickens infected with the JM strain. Early depression occurred 1 week postinfection and was followed by recovery a week later. The second depression occurred at 4 weeks postinfection and lasted until the end of the experiment. The GA strain-infected group, on the other hand, began to show depression 4 weeks postinfection, and most chickens died within a short time thereafter. PHA response of chickens infected with strain Md11/75C, attenuated in cell culture from highly virulent strain Md11, was almost the same as that of control chickens.