Macrophages RestrictPseudomonas aeruginosaGrowth, Regulate Polymorphonuclear Neutrophil Influx, and Balance Pro- and Anti-Inflammatory Cytokines in BALB/c Mice

Abstract

The role of macrophages in Pseudomonas aeruginosa corneal infection in susceptible (cornea perforates), C57BL/6 (B6) vs resistant (cornea heals), BALB/c mice was tested by depleting macrophages using subconjunctival injections of clodronate-containing liposomes before corneal infection. Both groups of inbred mice treated with clodronate-liposomes compared with PBS-liposomes (controls) exhibited more severe disease. In B6 mice, the cornea perforated and the eye became extremely shrunken, whereas in BALB/c mice, the cornea perforated rather than healed. The myeloperoxidase assay detected significantly more PMN in the cornea of both groups of mice treated with clodronate-liposomes vs PBS-liposomes. In independent experiments, ELISA analysis showed that protein levels for IL-1 beta, macrophage-inflammatory protein 2, and macrophage-inflammatory protein 1 alpha, all regulators of PMN chemotaxis, also were elevated in both groups of mice treated with clodronate-liposomes. Bacterial plate counts in B6 mice treated with clodronate-liposomes were unchanged at 3 days and were higher in control-treated mice at 5 days postinfection (p.i.), whereas in BALB/c mice, bacterial load was significantly elevated in the cornea of mice treated with clodronate-liposomes at both 3 and 5 days p.i. mRNA expression levels for pro (IFN-gamma and TNF-alpha)- and anti (IL-4 and IL-10)-inflammatory cytokines also were determined in BALB/c mice treated with clodronate-liposomes vs control-treated mice. Expression levels for IFN-gamma were significantly elevated in mice treated with clodronate-liposomes at 3 and 5 days p.i., while IL-10 levels (mRNA and protein) were reduced. These data provide evidence that macrophages control resistance to P. aeruginosa corneal infection through regulation of PMN number, bacterial killing and balancing pro- and anti-inflammatory cytokine levels.

The Role of CD1d-Restricted NKT Cells in the Clearance of Pseudomonas aeruginosa from the Lung Is Dependent on the Host Genetic Background

“…1A), consistent with previous reports demonstrating that BALB/c mice are more resistant to PAO1 infection (24)(25)(26). Interestingly, a comparison of BALB/c and BALB/c CD1d Ϫ/Ϫ mice revealed that BALB/c CD1d Ϫ/Ϫ mice were impaired in their ability to clear PAO1 from the lungs; a comparison of B6 to B6 CD1d Ϫ/Ϫ and B6 JA18 Ϫ/Ϫ mice revealed no such impairment (Fig.…”

Vasoactive Intestinal Peptide Balances Pro- and Anti-Inflammatory Cytokines in the Pseudomonas aeruginosa-Infected Cornea and Protects against Corneal Perforation

“…Data from our in vivo experiments revealed through MPO assay that PMN numbers were reduced in the cornea of rVIP-treated vs PBStreated mice after 3 and 5 days p.i. Previous studies by this laboratory suggest that M play a major role in regulating the influx and persistence of PMN in the cornea (24). Delgado and Ganea (31, 32) also have shown that VIP inhibits the production of MIP-2, a potent chemoattractant for PMN, by BALB/c-derived M .…”

“…It is of interest to note that not only were BALB/c-derived M more sensitive to the lower concentrations of rVIP (10 Ϫ10 /10 Ϫ9 vs 10 Ϫ8 M) compared with B6, but when stimulated with LPS alone, BALB/c M also displayed a significantly more robust response than B6 via proinflammatory cytokine/chemokine production of both IL-1␤ and MIP-2. It has been reported by this laboratory that depletion of the M in both BALB/c and B6 mouse strains before ocular infection with P. aeruginosa results in an exacerbated disease response, suggesting that M play a key role in regulating/balancing pro-and antiinflammatory activity in the resistant and susceptible models (24). Previous studies also have also suggested that M from Th1 T cell responder mouse strains (B6) are different regarding functional behavior (phagocytic activity, NO generation) when compared with those from Th2 strains (BALB/c) (26,27).…”

“…These data are consistent with previous studies indicating that VIP inhibits production of several proinflammatory cytokines and chemokines, including TNF-␣, IL-6, IL-1␤, IL-12, MIP-1, and MIP-2, while stimulating the production of anti-inflammatory cytokines IL-10 and IL-1R antagonist (15,16,19,22,23). In addition, we have previously used M depletion with clodronate and provided evidence that IL-10 is an important modulator of the resistant phenotype, functioning to balance IFN-␥ levels in the BALB/c cornea (24).…”

TREM-1 Amplifies Corneal Inflammation after Pseudomonas aeruginosa Infection by Modulating Toll-Like Receptor Signaling and Th1/Th2-Type Immune Responses

“…Activation of TLR signaling initiates a variety of inflammatory events, such as infiltration of inflammatory cells (e.g., polymorphonuclear neutrophils [PMNs] and monocytes/macrophages) (13,20,21,27), as well as the production of inflammatory cytokines (e.g., tumor necrosis factor alpha [TNF-␣], macrophage inflammatory protein 2 [MIP-2], interleukin-1␤ [IL-1␤], gamma interferon [IFN-␥], IL-6, and IL-12) (12,22). In bacterial keratitis, the TLR-induced inflammatory mediators promote bacteria clearance and induce tissue repair; however, if unbalanced or uncontrolled, they may amplify the host inflammatory response, leading to tissue damage and corneal perforation (12,24).…”