The blockage of proline incorporation by HF could activate amino acid starvation responses [16, 37], which consequently leads to caspase 3-dependent apoptosis as demonstrated in many previous studies [15, 16, 27], suggesting that cell apoptosis probably is the downstream pathway for HF-mediated suppression of cell growth, not only in anti-CD3 antibody-stimulated T cells but also in T cells even without antibody stimulation (i.e. non-stimulated control splenocytes, and Jurkat cells in Table 1). Here, CASP3 is linked to hydrops fetalis.