No abstract

Until recently it was believed that the T cell response of atopic dermatitis patients challenged with inhalant allergens originates almost exclusively and specifically from Th2 cells capable of secreting an abundance of interleukin (IL)-4 while producing no interferon (IFN)-gamma. To reevaluate this concept in a large cohort of atopic dermatitis patients we established 177 CD4+ T cell clones (45 of which showed specificity for house dust mite antigen) from the peripheral blood (n = 76), naturally occurring skin lesions (n = 40), and allergen-exposed skin (n = 61) of different patients. These clones were examined for their capacity to secrete IL-4 and IFN-gamma upon mitogenic stimulation. Moreover, 20 of these T cell clones were investigated for the synthesis of transcripts for IL-5, another Th cytokine. Our results indicate that the majority (52-100%) of allergen-specific T cells in both skin and blood of atopic individuals failed to exhibit a restricted cytokine secretion pattern and thus were classified as Th0 cells. House dust mite antigen specific T cells displaying a restricted secretion pattern (n = 16) were either of the Th1 or the Th2 type. Specific Th2 cells, however, were found almost exclusively in allergen patch test reactions, indicating that the Th2 differentiation pathway is seen preferentially in allergen-exposed skin. The cytokine secretion profile of T cell clones obtained from naturally occurring skin lesions showed similarity to those of patch test lesion, suggesting that the patch test represents a useful model to investigate the pathogenesis of atopic dermatitis.

The modulation of growth of normal and leukemic myeloid progenitor cells in soft agar cultures by recombinant human tumor necrosis factor-alpha (TNF alpha) and recombinant human interferon-gamma (IFN gamma) was investigated. TNF alpha inhibited colony formation of all colony types representing different maturational stages of normal progenitor cells committed to the myeloid lineage with different orders of sensitivity. Blast-type colonies derived from patients with acute myelogenous leukemia were more sensitive to TNF alpha inhibition than progenitor cells purified from normal bone marrow or bone marrow from patients with stable-phase chronic myelogenous leukemia. The response of most colony types to IFN gamma was poor. However, when IFN gamma was administered together with TNF alpha, synergistically enhanced antiproliferative effects were detected in all colony types tested. The antiproliferative action of IFN gamma on myelopoiesis was enhanced in culture by the presence of autologous monocytes, presumedly by inducing endogenous production of TNF alpha. However, TNF alpha seemed to act directly on the progenitor cells themselves to suppress their clonal growth, rather than involving accessory marrow elements such as monocytes and/or T lymphocytes.

T cells are known to interact cooperatively with monocytes to produce Colony-Stimulating Factors (CSF), although T cell-mediated signals leading to CSF secretion by monocytes are not completely understood. We have made use of Northern blot hybridization and specific bioassays to study the effects of the T cell product interleukin-4 (IL-4) on monocyte CSF expression. The results suggest a previously unrecognized role of IL-4 as a CSF inducer since exposure of monocytes to IL-4 resulted in accumulation of transcripts for granulocyte-CSF (G-CSF) and macrophage-CSF (M-CSF). Consequently, IL-4-activated monocytes released factors in their culture supernatants biologically and antigenically indistinguishable from G- and M-CSF.