ZAP70 and neoplasm: Alternative mechanisms leading to the aberrant expression of ZAP-70 relate to tumor-microenvironment mediated induction of ZAP-70: In B cells derived from peripheral blood, which have consistently low ZAP-70 levels, BCR-activating stimuli (e.g., anti-IgM, sCD40L, IL-4, IL-6, and IL-10) upregulate the expression of ZAP-70 (14).