T-cell and macrophage subsets in the bronchial wall of clinically healthy subjects

Abstract

This study was conducted to obtain quantitative data on the numbers of T- cells and macrophage subsets in the normal bronchial wall of man, and, thus, produce a baseline against which the numbers of these cells present in inflamed bronchi may be judged. Bronchial biopsies were obtained from 27 clinically healthy subjects attending hospital for elective orthopaedic operations. Eight of the subjects were smokers (median 3.5 pack-years), and eight were atopic as defined by skin prick test. Three to eight weeks after biopsy, subjects attended the lung function laboratory for spirometric testing and determination of provocative concentration of histamine producing a 20% fall in forced expiratory volume in one second (PC20FEV1). The bronchial biopsies were frozen and cryostat sections prepared. These sections were investigated with immunohistochemical techniques to reveal the presence and distribution of T-cell and macrophage subsets. Twenty six out of 27 subjects had spirometric values within the normal range, but a wide spectrum of bronchial reactivity was observed (PC20FEV1 range 2-36 mg histamine). Using monoclonal antibodies in immunohistological techniques, only small numbers of T-cells were seen, the majority being CD8+ cells in the epithelium. In the underlying tissue, CD4+ cells predominated (CD4/CD8 ratio, epithelium 1:9; underlying tissue 4:1). In both cases, approx. 50% of T- cells expressed the CD45Ro isotype. Small numbers of macrophages were observed in all samples. The majority of these cells expressed a 'suppressor cell' phenotype (RFD1+RFD7+), whilst only a small proportion (median 11%) exhibited the phenotype of antigen presenting cells (RFD1+RFD7-). Only very low levels of human leucocyte antigen-DR (HLA-DR) were recorded, both on the epithelium and underlying tissues. Smoking status and atopy did not influence the numbers and distribution of the T-cells and macrophages. These data offer, for the first time, a baseline against which the severity of immunopathological reactions in the bronchial wall may be evaluated.