Interleukin 5 expressing allergen-specific T-lymphocytes in patients with house dust mite sensitization: analysis at a clonal level.

Interleukin 5 (IL-5) is a T-cell lymphokine known to stimulate development, functional activity, and in vitro survival of eosinophils. Tissue and blood eosinophilia occurring during allergic responses of the immune system are potentially mediated by IL-5 secreting T-cells. To test this hypothesis a series of allergen-specific T-cell clones were established from peripheral blood and skin lymphocytes of patients with atopic dermatitis and house dust mite sensitization. In addition, alloreactive T-cell clones were also prepared from peripheral blood lymphocytes of healthy donors. Cloned T-cells were analyzed for IL-5 mRNA expression and IL-5 secretion by means of in vitro gene amplification using the reverse transcriptase polymerase chain reaction and IL-5 specific oligonucleotide hybridization, as well as IL-5-specific ELISA. A majority of allergen-specific long-term cultured T-cell clones (84%) of different donors and of either phenotype (CD8+ or CD4+) disclosed IL-5 transcripts on stimulation with lectins. Almost all clones exhibiting IL-5 transcripts also released immunoreactive IL-5 protein into their culture supernatants. In contrast, only 2% of alloreactive T-cell clones obtained from healthy donors and none of alloreactive T-cell clones of one atopic patient investigated expressed detectable amounts of IL-5 mRNA in response to lectin stimulation, all of whom were CD4+. These results suggest that eosinophilia observed in allergic responses in the peripheral blood and in tissues at the site of induced late-phase cutaneous reaction may be associated with IL-5 release by allergen-specific T-cells.