Antigen presentation in the lung: dendritic cells and macrophages

Antigen presentation is a required prime event before T-cell activation can occur. Cells which constitutively express major histocompatibility antigen class I or II an responsible for presenting antigens. These are essentiall y alveolar macrophages (AM) residing mostly in the air spaces, and dendriti c cells (DC), which create a tight surveillance network just below the epit helial cells of the airways and in the loose connective tissue around the v essels or in the pleura. AM are poor antigen presenting cells compared to D C. AM when encountering foreign particles or organisms may, however, influe nce the degree of activity or maturation of neighbouring DC, by releasing c ytokines. Thus, we will describe how the innate immune processes may influe nce specific immunity and perhaps Th1 and Th2 differentiation. Following th e description of the differences in phenotype and functions of AM and DC, w e will provide data showing that in some pathological conditions, such as s arcoidosis, AM can acquire some specificities of DC.