HUMAN LUNG MAST-CELL IL-5 GENE AND PROTEIN EXPRESSION - TEMPORAL ANALYSIS OF UP-REGULATION FOLLOWING IGE-MEDIATED ACTIVATION

The late-phase of allergic asthma is characterized by infiltration of the airway with eosinophils within 6 h of mast cell activation. Pro-eo sinophilic/pro-allergic (TH2) cytokines, originally described as T-lym phocyte products, have recently been ascribed to mast cells as well. T o date, however, it is unknown if TH2 cytokine gene expression by the human mast cells is subject to receptor-mediated regulation analogous to that of T-cells, and if messenger RNA (mRNA) expression results in protein secretion occurring in a temporal context consistent with the late-phase response. We examined interleukin-4 (IL-4), IL-5, and IL-6 mRNA expression induced by anti-IgE activation of human lung explants as assessed using reverse transcription/polymerase chain reaction (RT- PCR). Anti-IgE stimulation resulted in rapid and sustained upregulatio n of IL-5 message, but did not have analogous effects on IL-4 or IL-6. Using quantitative-competitive PCR, we demonstrated that 100 ng of to tal cellular RNA from human lung contained 1 fg of IL-5 mRNA; this inc reased to 100 fg 4 h after anti-IgE activation, The source of the anti -IgE-enhanced IL-5 mRNA is likely the mast cell itself, as anti-CD3 ac tivation oflung led to a dissimilar array of cytokine expression. In a ddition, human lung mast cells purified to near homogeneity expressed IL-5 mRNA after activation, as shown by both RT-PCR and in situ hybrid ization. In both lung fragments and purified human lung mast cells, th e modulation of IL-5 mRNA expression preceded the secretion of IL-5 pr otein, detected as early as 4 h after activation. Neither isolated pur ified mast cells nor purified peripheral blood T cells could be induce d to secrete detectable amounts of IL-5 protein when activated only wi th antibodies against IgE or CD3-T cell receptor complex, respectively . However, mast cells (n = 4) and T cells (n = 6) cultured at comparab le concentrations (4 x 10(6)/ml) activated through their respective an tigen receptors in the presence of phorbol ester yielded comparable IL -5 production (253 +/- 126 pg/ml versus 183 +/- 75 pg/ml, mean +/- SE) . We conclude that mast cells are analogous to T cells in the requirem ent of co-stimuli for the production of IL-5 protein. Moreover, the ra pid kinetics of IgE-mediated IL-5 transcription and protein elaboratio n are consistent with a primary role for mast cell activation directly leading to late-phase airway eosinophilia.