Mature MCs derived in vitro from CD34⁺ adult hematopoietic progenitors are resistant to infection with HIV. (A) FMF analysis of (CD117⁺) mature MCs derived from adult CD34⁺ hematopoietic progenitors in serum-free mast cell medium at 9 weeks in culture in vitro showed a lack of surface expression of CD4, CCR5, and CXCR4 (HIV) viral receptors and coreceptors. Black lines indicate cell populations treated with antigen-specific antibody; white lines indicate cell populations treated with isotype-matched control. (B) No detectable evidence by PCR of viral entry (SS cDNA) in mature MCs after challenge with either R5-tropic (HIV_BAL) or with X4-tropic (HIV_TYBE); LAD-2 control cells were susceptible to both HIV_BAL and HIV_TYBE. (C) Two separate cultures of productively infected HIV-infection resistant 9-week-old MCs express detectable levels of HIV p24 by ELISA. (D) Replication of infectious virus (HIV-p24⁺) could be reactivated in latently infected (HIV-p24 below detectable limits by ELISA) mature MCs. Activation of 13-week-old, latently infected mature MCs resulted in a dose-dependent elevation of HIV-p24 after signaling through TLR2, TLR4, TLR9, or after FcϵRIα coaggregation. (E) Latently infected 13-week-old mature MCs showed undetectable levels of HIV FL or MS mRNA that was significantly elevated (4-6 × 10⁵-fold) after activation by IgE cross-linking. All experiments were performed a minimum of 3 times. All error bars represent standard deviation of the mean of replicate PCR reactions at each data point.