ABNORMAL ALVEOLAR MACROPHAGE POPULATIONS IN BONE-MARROW TRANSPLANT RECIPIENTS WITH PNEUMONITIS

The purpose of this investigation was to determine whether there is an y relationship between different subsets of alveolar macrophages and t ype of infection or survival from interstitial pneumonitis following b one marrow transplantation (BMT). The population of alveolar macrophag es found in bronchoalveolar lavage fluid (BALF) from 16 BMT recipients with 19 episodes of interstitial pneumonitis was investigated, using immunocytochemical methods. Results were compared with those from seve n normal volunteers. The results showed that patients with pneumonitis had significantly higher numbers of total cells in BALF than normals but reduced proportions of macrophages, although the absolute numbers were unchanged. Of the cells present which were morphologically macrop hages, there were raised proportions of both RFD1+ cells (interdigitat ing cells) and RFD7+ cells (mature macrophages) in patients compared w ith normals, but expansion of these two subsets could be explained in part, by a significant increase in cells positive for both markers (42 % in patients compared with 9% in normals). Proportions of cells with the monocyte phenotype (CD14+, UCHM1) were also significantly raised i n patients with pneumonitis (17% compared with 6% in normals). These p atients, however, had significantly reduced proportions of macrophage- like cell which were positive for the DR antigen (Class II major histo compatibility complex (MHC) antigen) (47% compared with 88% in normals ), and this abnormality was greater still in patients who died from pn eumonitis (40%) compared with those who survived (52%). The results of this study indicate a breakdown of local immunoregulation, thus contr ibuting to the high incidence of, and mortality from, opportunistic pu lmonary infections in this group.