OBJECTIVETo examine whether lipopolysaccharide (LPS)-induced apoptosis correlates with TNF-alpha release by type II alveolar epithelial cells (AEC II), whether TNF-alpha knockout (TNF KO) abrogates the induction of apoptosis by LPS and whether TNF-alpha is sufficient to induce apoptosis in this cell type.

METHODSAEC II were isolated from wild type mice and TNF KO mice. Cells were stimulated with LPS or recombinant murine TNF-alpha for 24 h. TNF-alpha in culture supernatant was determined by ELISA following LPS stimulation. Apoptosis was determined by the terminal deoxynucleotidyl transferase end-labeling (TUNEL) assay after treatment with either LPS or TNF-alpha.

RESULTSLPS induced apoptosis in wild type AEC II in a concentration-dependent manner. LPS-induced AEC II apoptosis was accompanied by an 11-fold increase (from 0.073 +/- 0.065 ng/ml in control to 0.94 +/- 0.14 ng/ml in 50 micro g/ml of LPS, P < 0.01) in TNF-alpha release. However, increasing concentrations (5 or 25 ng/ml) of recombinant murine TNF-alpha failed to induce AEC II apoptosis. In addition, apoptosis did occur in AEC II isolated from TNF KO mice following LPS stimulation.

CONCLUSIONSThis study confirms that LPS induces TNF-alpha release and apoptosis in murine AEC II in vitro. Exogenous TNF-alpha failed to induce AEC II apoptosis, and apoptosis occurred following LPS stimulation in cells lacking the ability to produce TNF-alpha. Taken together, these results suggest that LPS-induced AEC II apoptosis occurs by a TNF-alpha-independent mechanism.