Allergic sensitization in asthma develops as a consequence of complex inter
actions between T cells and antigen-presenting cells. We have developed sev
eral in vivo models to study allergen-specific T cell and B cell function a
nd their relevance to allergic airway hyperresponsiveness (AHR), focusing o
n the role of the costimulatory molecules CD80 and CD86. Treatment of mice
with anti-CD86, but not anti-CD80, significantly inhibited increased serum
levels of ovalbumin (OA)-specific IgE and IgG(1), airway eosinophilia, and
AHR both after 10 d of OA aerosol exposure (in the absence of adjuvant) and
after intraperitoneal sensitization followed by repeated airway challenges
. Inhibition of AHR was associated with decreased IL-4 and IL-5 levels in t
he BAL fluid of sensitized mice, suggesting impaired Th2 function in anti-C
D86-treated animals. This effect was not seen when mice received treatment
only before allergen challenge, indicating that anti-CD86 acts through inhi
bition of allergic sensitization and not simply by inhibiting the influx of
inflammatory cells. These data suggest that the CD86 costimulatory ligand
plays a major role in the development of allergic inflammation and AHR in a
llergen-challenged mice. Further, this study demonstrates that T-B cell int
eractions during allergic sensitization are amenable to therapeutic manipul
ation and that selective blockade of accessory signals can be an effective
means for modulating distinct T cell functions.