L-plastin is essential for alveolar macrophage production and control of pulmonary pneumococcal infection.

We report that mice deficient for the hematopoietic-specific, actin-bundling protein L-plastin (LPL) succumb rapidly to intratracheal pneumococcal infection. The increased susceptibility of LPL(-/-) mice to pulmonary pneumococcal challenge correlated with reduced numbers of alveolar macrophages, consistent with a critical role for this cell type in the immediate response to pneumococcal infection. LPL(-/-) mice demonstrated a very early clearance defect, with an almost 10-fold-higher bacterial burden in the bronchoalveolar lavage fluid 3 h following infection. Clearance of pneumococci from the alveolar space in LPL(-/-) mice was defective compared to that in Rag1(-/-) mice, which lack all B and T lymphocytes, indicating that innate immunity is defective in LPL(-/-) mice. We did not identify defects in neutrophil or monocyte recruitment or in the production of inflammatory cytokines or chemokines that would explain the early clearance defect. However, efficient alveolar macrophage regeneration following irradiation required LPL. We thus identify LPL as being key to alveolar macrophage development and essential to an effective antipneumococcal response. Further analysis of LPL(-/-) mice will illuminate critical regulators of the generation of alveolar macrophages and, thus, effective pulmonary innate immunity.

Peptide-mediated activation of Akt and extracellular regulated kinase signaling prevents lymphocyte apoptosis.

Lymphocyte apoptosis is a hallmark of sepsis and contributes to disease mortality. In other acute injuries, such as myocardial and cerebral ischemia/reperfusion, apoptosis plays a significant role in disease-associated morbidity and mortality. We previously showed that constitutive activation of the potent antiapoptotic Akt/protein kinase B signaling pathway in lymphocytes both reduces sepsis-induced lymphocyte apoptosis and confers a significant survival advantage compared to wild-type littermates. Here, we demonstrate a therapeutic approach to acutely augment Akt activity in a wild-type animal. A cell-permeable peptide conjugated to the Akt-binding domain of the endogenous Akt coactivator, Tcl-1, prolongs Akt activity, activates extracellular regulated kinase (ERK) signaling and protects lymphocytes from numerous apoptotic stimuli both in vitro and in vivo. Molecular approaches to activate the antiapoptotic Akt and ERK signaling pathways may provide a novel tool to study these signaling pathways, as well as a new antiapoptotic strategy for the treatment of sepsis and other acute injuries.

Anti-apoptotic peptides protect against radiation-induced cell death.

The risk of terrorist attacks utilizing either nuclear or radiological weapons has raised concerns about the current lack of effective radioprotectants. Here it is demonstrated that the BH4 peptide domain of the anti-apoptotic protein Bcl-xL can be delivered to cells by covalent attachment to the TAT peptide transduction domain (TAT-BH4) and provide protection in vitro and in vivo from radiation-induced apoptotic cell death. Isolated human lymphocytes treated with TAT-BH4 were protected against apoptosis following exposure to 15Gy radiation. In mice exposed to 5Gy radiation, TAT-BH4 treatment protected splenocytes and thymocytes from radiation-induced apoptotic cell death. Most importantly, in vivo radiation protection was observed in mice whether TAT-BH4 treatment was given prior to or after irradiation. Thus, by targeting steps within the apoptosis signaling pathway it is possible to develop post-exposure treatments to protect radio-sensitive tissues.