CD4 counts in the blood paralleled virus burden in plasma in that most animals showing viral rebound within the first 5 months after stopping ART exhibited CD4 decline by the end of the study to levels that were below 50% of the baseline level measured prior to infection whereas all animals that contained viral rebound for at least 5 months after drug was stopped showed stable CD4+ lymphocyte counts for the duration of the study (Fig. 3). Here, CD4 is linked to infection.