Cystatin C-deficient APCs have a greater propensity to stimulate cystatin C-sufficient T cells. Splenocytes were prepared from either cystatin C-deficient mice or wild type mice and stimulated in vitro with either media alone or with 2 ug/mL ConA (change in production level (delta) is shown, where the response to media alone is deducted from the ConA response). Cystatin C-deficient splenocytes mice (CysC-/-) had a significantly higher production of IL-2 (A) after 24 h Cystatin C-deficient APCs were able to enhance the IL-2 production of T cells from wild type mice, where as there was no difference in IL-2 production in cystatin C-deficient T cells when co-cultured with either wild type (CysC+/+) or cystatin C-deficient APCs (B). However, when wild type APCs where co-cultured with T cells then the cystatin C-deficient T cells produced more IL-2 than wild type T cells. Six mice were used per group, statistical significance was calculated by Students t-test where * P-value < 0.05 and ** P-value < 0.01.