The limited available data for patients with SCD suggest that lymphocyte proliferation can be reduced, normal, or occasionally increased compared to subjects without SCD.30-32 Differences in lymphocyte proliferation between patients with SCD and subjects without SCD may be related to disease severity (concentrations of sickle [S] and fetal [F] Hb), spleen dysfunction, undernutrition, frequent pain crisis episodes, or infection.32 This evidence concerns the gene GSTM1 and infection.