Autocrine regulation of cord blood-derived human mast cell activation by IL-10

Background: Ligation of the high-affinity receptor for IgE on human mast ce lls (MCs) induces the release of proinflammatory mediators, including vasoa ctive amines and cytokines (TNF-alpha, IL-5, and IL-8). Moreover, we have r ecently shown that IL-10 inhibits the release of proinflammatory mediators by activated MCs. Objective: We investigated whether human cord blood-derived MCs (CBMCs) cou ld produce IL-10 and whether this production could inhibit their activation in an autocrine fashion. Methods: IL-10 synthesis by resting or activated human MCs derived from cor d blood progenitors was investigated in cell supernatants or by using immun ostaining and RT-PCR methods. In addition, the effect of IL-4 on such synth esis was also studied. Anti-IL-10-neutralizing antibodies were used to inve stigate the validity of the hypothesis of an autocrine regulation of MCs by IL-10. Finally, the presence of specific receptors for IL-10 was searched on human CBMCs by using flow cytometric analysis. Results: Human CBMCs spontaneously synthesize and release IL-10, and this s ynthesis is increased after IgE/anti-IgE stimulation. In addition, the pres ence of IL-10 in resting or in activated MCs was proved by immunostaining. Interestingly, the release of IL-10 was also increased after incubation of the cells with IL-4. Besides, the use of neutralizing antibodies against IL -10 confirmed that IL-10 released inhibited MC activation in an autocrine f ashion. Finally, the presence of specific receptors for this cytokine was o bserved on the membranes of our population of human CBMCs. Conclusion: Taken together, our data are in favor of an autocrine regulatio n pathway through synthesis and release of IL-10 by human MCs. Such an auto regulatory mechanism is, to our knowledge, the first described for these el ements.