Inhibition of T cell proliferation by human alveolar macrophages.

The demonstration by Upham et al that human alveolar macrophages selectively inhibit proliferation of T cells by secretion of unidentified eVector molecules raises the question as to whether pathological processes in the lung characterised by extensive macrophage recruitment or activation can have a systemic eVect on T cell development. It has been shown in several studies that patients with pulmonary tuberculosis who are not infected by HIV often show a lymphopenia principally aVecting the CD4+ T cells. 3 This appears to be a transient phenomenon as the CD4+ count reverts to normal after successful therapy. A similar transient CD4+ lymphopenia has also been observed after antigenic bronchial provocation in asthmatic subjects. It would be of great interest to determine whether this systemic phenomenon is due to the same mechanism as the one described by Upham et al, whether it accounts (at least in part) for the so-called “idiopathic CD4+ T lymphopenia syndrome”, and whether it aVects the balance between Th1 and Th2 cells which may be critical to the pathogenesis of both asthma and tuberculosis.