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In this study, we investigated the importance of the beta 2-integrins for the development of tracheal hyperreactivity in a murine model for nonallergic asthma. The response was induced by skin sensitization with dinitrofluorobenzene (DNFB) followed by an intranasal challenge with the same hapten. Twenty-four hours after the challenge, tracheal hyperreactivity, a decrease in T cells in the blood, and increased neutrophil numbers in bronchoalveolar lavage fluid (BALF) and blood were observed. Monoclonal antibodies (mAbs) directed against the alpha-chains of LFA-1 (FD441.8) and Mac-1 (M1/70) were injected intravenously 2 h before and 2 h after the challenge. Treatment with anti-LFA-1 mAb totally inhibited the development of tracheal hyperreactivity measured 24 h after the challenge, whereas anti-Mac-1 mAb had only a partial effect on this response. The decrease in T cells in the blood, which was also evident 24 h after the challenge, was totally inhibited by treatment with anti-LFA-1, whereas anti-Mac-1 had little effect. The increase in the number of neutrophils in BALF at this time point was completely inhibited by both anti-LFA-1 and anti-Mac-1. In summary, evidence presented in this report highlights the possible importance of the adhesion molecule LFA-1 in the development of tracheal hyperreactivity. Our results suggest that LFA-1 present on T cells may play an integral role in this response.