Tolerance to Contact Al lergens in Mice : A Funct ional Ro le for CD 8 § T Helper Type 2 Cells

Normal skin is permeable to low molecular hydrophobic substances, including allergenic chemicals. Whereas such foreign matter appears to enter the skin naturally, it rarely induces contact hypersensitivity. This suggests that immunological tolerance would be the normal state o f affairs. In search o f a suitable model, we painted picryl chloride or oxazolone once or repeatedly on normal skin o f BALB/c or C57B1/6 mice and found subsensitizing doses to be tolerogenic. The most effective doses in inducing tolerance were doses between those at the point o f inflection from no responses to threshold sensitivity. But even doses three orders of magnitude lower than these suppressed subsequent sensitization if applied repeatedly. C57B1/6 mice (low responders) were consistently easier to make tolerant than B A L B / c mice (high responders). The tolerant state established by a single painting was found to be fully developed at 48 h after initiation and long-lasting (> 14 d). It could be adoptively transferred by intravenous injection of total spleen cells (SC), lymph node cells (LNC), or purified T cells and shown to be hapten specific. Pretreatment with cyclophosphamide (Cy) prevented tolerization. The T cells capable of transferring suppressive activity were found to be generated irrespective of the dose applied. O n day 2 after painting, tolerance could be transferred with L N C from both tolerant and sensitized animals. O n day 5, however, only cells f rom tolerant donors transferred tolerance. But by action o f Cy, suppression was shown to be part o f every sensitization, although masked. Production ofhapten-specific antibodies was suppressed as well. Through depletion by m o n o clonal antibody in vitro the T suppressor cells were shown to belong to the murine CD8 + subset (Lyt2+). U p o n restimulation in vitro by haptenized and irradiated normal SC, L N C from tolerant donors produced predominantly interleukin (IL)-4, IL-5, and IL-10. In contrast, L N C from sensitized donors produced preferentially IL-2 and interferon-"/. Thus we demonstrate that painting subsensitizing doses o f contact sensitizers on normal murine skin generates CD8 + Th2-1ike cells that give rise to hapten-specific tolerance. The model may have broader significance and apply to other species, including humans.