Cell-mediated immune kinetics in experimental bronchiectasis

Abstract

In a recently developed rat model of bronchiectasis (BX) generated by partial bronchial ligation and injection of Pseudomonas aeruginosa (Pa), the composition and distribution of immunocompetent cells were analysed at progressive timeintervals by immunohistochemical methods. Four groups of 25 animals were prepared: 1) Partial ligation and injection of Pa (Pa+LIG); 2) Injection of Pa without bronchial ligation (Pa+NOLIG); 3) Sham operated (S); 4) Age-matched normal controls (N). Bronchiectasis developed in 22/25 animals of the Pa+LIG group but in none of the 75 controls of the other 3 groups. This bronchial dilation began within 2 weeks and was accompanied by a T- lymphocyte proliferation beginning in the bronchus-associated lymphoid tissue (BALT). Up to week 4 this was composed mainly of CD4+ve cells. Large de novo lymphoid aggregates appeared in the lung parenchyma, with an initial (2–4 wks.) predominance of CD4+ cells. From week 8 onwards, a predominance of CD8+ cells was noted in both areas. The bronchial lamina propria of rats from the Pa+LIG group was infiltrated by significantly larger numbers of T-lymphocytes (mainly of CD8+ phenotype) and macrophages when compared with the other 3 groups, at all time points. The bronchial epithelium of 17/22 animals showing bronchial dilation in the Pa+LIG group expressed Ia antigen but that of the 75 animals in the other groups did not. These findings support the hypothesis that chronic inflammation in bronchiectasis is associated with a cell-mediated immune response developing as a consequence of bacterial infection in an airway where the clearance mechanisms have been impaired.