T-LYMPHOCYTE RESPONSES TO PLICATIC ACID HUMAN SERUM-ALBUMIN CONJUGATEIN OCCUPATIONAL ASTHMA CAUSED BY WESTERN RED CEDAR

Background: T cells are known to play a major role in the pathogenesis of atopic allergic asthma, but it is less clear whether they are invo lved in occupational asthma caused by low molecular weight chemicals s uch as plicatic acid. Objectives: We sought to determine whether perip heral blood T cells from patients with western red cedar asthma (WRCA) recognize plicatic acid (PA) conjugated to human serum albumin (HSA) as judged by proliferation or cytokine production and to analyze the r esponse to PA inhalation with flow cytometry. Results: Significant pro liferative responses to PA-HSA were observed in eight of 33 patients w ith WRCA, none of 10 exposed nonasthmatic cedar workers, and one of 18 nonasthmatic control subjects. Two of 25 patients with WRCA also show ed proliferative responses to unconjugated PA. All the WRCA responders were either currently exposed to cedar or had ceased exposure within the preceding 2 years. None of the four patients receiving oral steroi ds responded, but inhaled steroids did not seem to influence responsiv eness. No correlations were found between the maximum stimulation resp onse and any of the current FEV1 values, the current PC20 methacholine values, or the magnitude of the late asthmatic response to PA. Periph eral blood T-cell subset proportions and their degree of activation we re similar in patients with WRCA and exposed control subjects. There w as no change in T-cell phenotypes or their activation markers after PA inhalation challenge. In vitro, PA-HSA stimulation did not affect sub set ratios but led to release of small amounts of IL-5 and IFN-gamma, with no detectable increase in IL-4. Conclusions: PA-HSA-specific T ly mphocytes seem to be present in small numbers in the peripheral blood of patients with WRCA and may respond to antigenic exposure by produci ng IFN-gamma and IL-5, However, the proportion of responding cells wou ld appear to be lower than in comparable studies of atopic asthma.