CD28 and heart failure: Moreover, our results showed that CARD CP had lower CD8+ proliferative response to PHA, low level of T cells expressing CD28+ cells, lower expression CD3ζ (CD3ζ bright/CD3ζ dim Ratio) and still higher fractions of activated T cells than individuals with non-chagasic cardiomyopathy; suggesting that parasite persistence, more than the systemic changes derived from heart failure, are associated with these cellular immune abnormalities.