Apoptotic response of eosinophils in chronic eosinophilic pneumonia

To clarify the pathogenesis of chronic eosinophilic pneumonia (CEP), the ap optosis of eosinophils from bronchoalveolar lavage (BAL-Eos) was compared w ith that of eosinophils from peripheral blood (PB-Eos) in six cases of CEP, The survival rate of eosinophils and the percentage of apoptotic cells of b oth types of eosinophils were examined, and the effects of interleukin 5 (I L-5) were evaluated. The role of Fas expression in apoptosis of these eosin ophils was also studied. The survival rate of BAL-Eos on the third day of culture was significantly higher than that of PB-Eos (p < 0.01), This was associated with a lower pro portion of apoptotic cells in BAL-Eos than in PB-Eos; the percentages of ap optotic cells in PB-Eos and BAL-Eos after 24 h of incubation were 21.7 <plu s/minus> 3.4% and 10.6 +/- 1.7% respectively, IL-5 suppressed apoptosis and increased the survival rate of both PE-Eos and BAL-Eos, It was found that the apoptotic character of BAL-Eos differed from that of PB-Eos in at least three ways, Firstly, the positive rate of Fas expression on PB-Eos was inc reased after 24 h of incubation, whereas that on BAL-Eos did not change. Se condly, the expression of Fas on PB-Eos was suppressed by IL-5 (18.5 +/- 4. 2% - 8.3 +/- 3.2%, p < 0.05), whereas IL-5 failed to suppress Fas expressio n on BAL-Eos (3.3 <plus/minus> 1.6% - 3.6 +/- 1.0%). Lastly, binding of ant ibody to Fas antigen induced apoptosis of PB-Eos, but not of BAL-Eos. These data suggested that Fas seemed to be involved in the apoptosis of PE- Eos, whereas BAL-Eos were Fas-resistant in chronic eosinophilic pneumonia, In conclusion, apoptosis of eosinophils might he suppressed by proinflammat ory cytokines such as IL-5 leading to their accumulation in the lung. Chron ic stimulation of eosinophils in the alveolar space with IL-5 may play a cr ucial role chronic eosinophilic disorders.