Pre-induction of heat shock protein 70 (HSP70) is known to effectively attenuate the lipopolysaccharide (LPS)-induced inflammatory response in lung tissue. However, it is unclear if HSP70 induction after LPS exposure attenuates the subsequent LPS-induced inflammatory response in alveolar epithelial cells. This study examined the effects of HSP70 induction after LPS exposure on the IL-6 production and the cell viability after a subsequent LPS challenge in murine alveolar epithelial cells, and investigated whether or not HSP70 itself may be involved in those effects.

Murine alveolar epithelial cells were cultured and divided into two groups; the Non-Pre-LPS group without a LPS pre-treatment and the Pre-LPS group with a LPS pre-treatment. Each group was subdivided into the following four subgroups: subgroup C (control), subgroup Q (quercetin), subgroup HSP70 (HSP70 induction), and subgroup HSP70-Inh (HSP70 inhibition). HSP70 expression, which was induced by sodium arsenite and inhibited by quercetin, was analyzed by western blot analysis. The IL-6 levels in the culture supernatant were measured by ELISA, and the cell viability was measured using a simplified MTT assay.

The IL-6 levels were lower in subgroup HSP70 than in subgroup C (P<0.01), and were higher in subgroup HSP70-Inh than in subgroup HSP70 in both the Non-Pre-LPS and Pre-LPS groups (P<0.05, P<0.01). The cell viability tended to decrease in the Pre-LPS group compared with the Non-Pre-LPS group. While the cell viability was higher in subgroups Q, HSP70, and HSP70-Inh than in subgroup C in the Non-Pre-LPS group (P<0.05, P<0.05, P<0.01), there was no difference in cell viability among the subgroups in the Pre-LPS group.

HSP70 induction after a LPS pre-treatment in murine alveolar epithelial cells inhibits the subsequent LPS-induced IL-6 production without affecting the cell viability, and HSP70 by itself may play an important role in this proccess.