Alveolar epithelial cells type II (AEC-II) express MHC class II on their su
rface, an important prerequisite for antigen presentation. However, accesso
ry signals are required for an efficient T-cell activation. We therefore is
olated AEC-II from tumor-free sections of human lungs obtained by lobectomy
/pneumectomy and purified the cells by magnetic-activated cell sorting. Fur
thermore, we tested the expression of CD54, CD58, CD80, and CD86 on AEC-II
and evaluated their accessory function (AF) in cell culture using a cocultu
re of interleukin-2 (IL-2), releasing Jurkat cells and AEC-II. An increased
AF is documented by an elevated IL-2 release and expressed as accessory in
dex (AI), In 33 experiments the AF of AEC-II proved to be highly variable.
AI ranged between 0.3 and 17.1 with a median of 1.4 (0.3-17.1), Forty-four
percent (4-77) of the AEC-II expressed HLA-DR, 44% (12-89%) of the cells ex
pressed CD58, and CD54 was expressed by 55% (16-89%). AEC-II also expressed
CD80 and CD86 (38% [0-77%] and 40% [4-68%], respectively), Interestingly,
AEC-II released high levels of TGF beta (1730 pg/mL [771-5876]) and the acc
essory index could be increased (approximate to 2-fold) by the addition of
neutralizing anti-TGF beta antibodies or radiation. Thus, type II alveolar
cells express costimulatory molecules and are able to deliver costimulatory
signals for T cells, providing evidence that AEC-II are able to act as ant
igen-presenting and immunoregulatory cells of the lung. Additionally, the a
ccessory function of AEC-II is under the control of endogenously released T
CF beta.