Alveolar macrophages are a major determinant of early responses to viral lung infection but do not influence subsequent disease development.

Macrophages are abundant in the lower respiratory tract. They play a central role in the innate response to infection but may also modulate excessive inflammation. Both macrophages and ciliated epithelial cells respond to infection by releasing soluble mediators, leading to the recruitment of innate and adaptive effector cells. To study the role of lung macrophages in acute respiratory viral infection, we depleted them by the inhalation of clodronate liposomes in an established mouse model of respiratory syncytial virus (RSV) disease. Infection caused an immediate local release of inflammatory cytokines and chemokines, peaking on day 1, which was virtually abolished by clodronate liposome treatment. Macrophage depletion inhibited the activation (days 1 to 2) and recruitment (day 4) of natural killer (NK) cells and enhanced peak viral load in the lung (day 4). However, macrophage depletion did not affect the recruitment of activated CD4 or CD8 T cells, weight loss, or virus-induced changes in lung function. Therefore, lung macrophages play a central role in the early responses to viral infection but have remarkably little effect on the adaptive response occurring at the time of peak disease severity.

The chemokine MIP1alpha/CCL3 determines pathology in primary RSV infection by regulating the balance of T cell populations in the murine lung.

BACKGROUND: CD8 T cells assist in the clearance of respiratory syncytial virus (RSV) infection from the lungs. However, disease after RSV infection is in part caused by excessive T cell activity, and a balance is therefore needed between beneficial and harmful cellular immune responses. The chemokine CCL3 (MIP1alpha) is produced following RSV infection and is broadly chemotactic for both T cells and natural killer (NK) cells. We therefore investigated its role in RSV disease. METHODOLOGY/PRINCIPAL FINDINGS: CCL3 was produced biphasically, in both the early (day 1) and late (day 6-7) stages of infection. CCL3 depletion did not alter the recruitment of natural killer (NK) cells to the lungs during the early stage, but depletion did affect the later adaptive phase. While fewer T cells were recruited to the lungs of either CCL3 knockout or anti-CCL3 treated RSV infected mice, more RSV-specific pro-inflammatory T cells were recruited to the lung when CCL3 responses were impaired. This increase in RSV-specific pro-inflammatory T cells was accompanied by increased weight loss and illness after RSV infection. CONCLUSIONS/SIGNIFICANCE: CCL3 regulates the balance of T cell populations in the lung and can alter the outcome of RSV infection. Understanding the role of inflammatory mediators in the recruitment of pathogenic T cells to the lungs may lead to novel methods to control RSV disease.

Identification of major outer surface proteins of Streptococcus agalactiae.

To identify the major outer surface proteins of Streptococcus agalactiae (group B streptococcus), a proteomic analysis was undertaken. An extract of the outer surface proteins was separated by two-dimensional electrophoresis. The visualized spots were identified through a combination of peptide sequencing and reverse genetic methodologies. Of the 30 major spots identified as S. agalactiae specific, 27 have been identified. Six of these proteins, previously unidentified in S. agalactiae, were sequenced and cloned. These were ornithine carbamoyltransferase, phosphoglycerate kinase, nonphosphorylating glyceraldehyde-3-phosphate dehydrogenase, purine nucleoside phosphorylase, enolase, and glucose-6-phosphate isomerase. Using a gram-positive expression system, we have overexpressed two of these proteins in an in vitro system. These recombinant, purified proteins were used to raise antisera. The identification of these proteins as residing on the outer surface was confirmed by the ability of the antisera to react against whole, live bacteria. Further, in a neonatal-animal model system, we demonstrate that some of these sera are protective against lethal doses of bacteria. These studies demonstrate the successful application of proteomics as a technique for identifying vaccine candidates.