FIG. 5.

Proliferative responses to FIV antigen of individual cats immunized with FIV-RBC (solid bars) or BSA-RBC (open bars). (A) Response at the time of first challenge (4 months after completion of primary immunization). (B) Response at the time of second challenge (2 months after a booster dose of immunogen). The SI is the ratio of radioactivity incorporated by PBMC in the presence of the antigen to that incorporated in the absence of the antigen. Only values of ≥2 were considered indicative of FIV-specific lymphoproliferation. In the absence of antigen, values ranged between 177 and 4,488 cpm in individual cats.