Alveolar macrophages from HIV-infected patients with pulmonary tuberculosis retain the capacity to respond to stimulation by lipopolysaccharide

The functional capacity of alveolar macrophages (AM) in human immunodeficiency virus (HIV)-infected patients with pulmonary tuberculosis (TB) is not completely understood. To investigate the capacity of AM to mediate inflammatory responses, we obtained AM from human subjects by bronchoalveolar lavage (BAL) and studied the cells ex vivo. We compared AM from HIV-infected patients with suspected pulmonary TB to AM from healthy, HIV-negative controls for their capacity to produce TNF-α or IL-6 spontaneously and upon stimulation with lipopolysaccharide (LPS). Cytokine-producing cells were identified by macrophage markers and intracellular cytokine staining and flow cytometry. A higher proportion of AM from patients with microbiologically confirmed pulmonary TB than patients with probable TB or controls spontaneously expressed TNF-α shortly after isolation (geometric means: 38.5%, 23.7% and 15.8%, respectively), suggesting endogenous cytokine production. The proportions of AM spontaneously expressing TNF-α positively correlated with peripheral blood CD4+ T-lymphocyte counts in patients (partial r = 0.60, p = 0.003) but not controls. Stimulation with LPS resulted in a significant increase in the proportions of TNF-α- and IL-6-positive AM from patients and controls (p < 0.01). Bronchoalveolar lavage fluid (BALF) from confirmed TB patients also contained higher concentrations of the inflammatory cytokines predominantly produced by macrophages, IL-6 and IL-8, than controls (geometric mean cytokine concentrations per gram of BALF albumin were 1291 pg/g vs. 115 pg/g, p = 0.03 for IL-6 and 4739 pg/g vs. 704 pg/g, p = 0.03 for IL-8). We concluded that AM from HIV-infected patients with pulmonary TB produced and released inflammatory cytokines in vivo and retained their innate ability to respond to stimulation by LPS.