Resident CD8+ T cells suppress CD4+ T cell-dependent late allergic airway responses

Background: The role of CD8(+) T cells in the immune response to airway challenge with an allergen is poorly understood. Objective: The aim of this study was to test the hypothesis that resident naive CD8(+) T cells modulate the magnitude of CD4(+) T cell-dependent allergic airway responses. Methods: Cervical lymph node CD4(+) T cells (2 X 10(6)) were harvested from ovalbumin (OVA)- or sham-sensitized rats and injected intraperitoneally into naive Brown Norway recipients. The recipients were treated with a CD8 alpha mAb (OX-8) to deplete the resident CD8+ T cells (n = 12) or mouse ascites (n = 12). Two days after adoptive transfer, the recipient animals were OVA challenged, lung resistance was measured for 8 hours, and bronchoalveolar lavage (BAL) was performed. Results: After OVA challenge, primed CD4-transferred CD8-depleted rats had larger early airway responses and late airway responses compared with primed CD4-transferred CD8-nondepleted rats (early airway responses: 158.6% +/- 19.2% vs 115.7% +/- 5.9%, P < .05; late airway responses: 8.5% +/- 1.7% vs 4.4% +/- 0.9%, P < .05). BAL eosinophilia was also greater (4.67% +/- 0.45% vs 2.34 +/- 0.26%, P < .01). The cells in BAL fluid expressing IL-4 mRNA were not significantly changed by CD8 depletion, but IL-5 mRNA(+) cells were higher in number, and IFN-gamma mRNA+ cells were fewer in the CD8-depleted group. Conclusions: Resident CD8(+) T cells downregulate the late allergic response and airway inflammation evoked by CD4(+) T-cell transfers in Brown Norway rats. This downregulation does not require antigen priming.