Cytokines as targets of immunotherapy in bacterial pneumonia

Ensuring animal welfare while meeting scientific aims using a murine pneumonia model of septic shock

With animal models, death as an intentional end point is ethically unacceptable. However, in the study of septic shock, death is still considered the only relevant end point. We defined eight humane end points into four stages of severity (from healthy to moribund) and used to design a clinically relevant scoring tool, termed "the mouse clinical assessment score for sepsis" (M-CASS). The M-CASS was used to enable a consistent approach to the assessment of disease severity. This allowed an ethical and objective assessment of disease after which euthanasia was performed, instead of worsening suffering. The M-CASS displayed a high internal consistency (Cronbach α = 0.97) with a high level of agreement and an intraclass correlation coefficient equal to 0.91. The plasma levels of cytokines and markers of oxidative stress were all associated with the M-CASS score (Kruskal-Wallis test, P < 0.05). The M-CASS allows tracking of disease progression and animal welfare requirements.

Sequence of immunoglobulin isotype exposure modulates inflammatory response to bacteria and lipopolysaccharide in vitro

BACKGROUND

Secretory immunoglobulin A (sIgA) and immunoglobulin G (IgG) are the principal immunoglobulins in the respiratory tract. Under normal circumstances, the upper respiratory tract contains predominantly sIgA, whereas IgG is of primary importance in the lower tract. Unlike other antibody isotypes, IgA antibodies participate in host defense functions without inciting inflammatory processes that might cause collateral damage to tissues. However, the ability of sIgA to modulate inflammatory reactions induced by other humoral factors is unclear. We examined the effect of the sequence of exposure to the two immunoglobulin isotypes on bacteria- or lipopolysaccharide (LPS)-mediated cytokine production by monocyte-polymorphonuclear neutrophil (PMN) cells in vitro.

METHODS

Blood monocytes were co-cultured with Escherichia coli or LPS. Either sIgA or IgG was added to subsets of cultures, which were incubated for 1 h at 37 degrees C. Culture supernatant liquids were then co-cultured with naïve PMNs for 1 h at 37 degrees C. Either IgG was added during this co-culture step or sIgA was added if IgG was added first. Cytokines were quantitated by enzyme-linked immunosorbent assay.

RESULTS

Significant increases in interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and IL-8 were noted after E. coli or LPS co-culture with monocytes and subsequent PMN challenge. Marked decreases in these pro-inflammatory cytokines were seen after the addition of sIgA or sIgA-IgG but not after IgG alone. This effect was more apparent with the immunoglobulin sequence IgA followed by IgG.

CONCLUSION

The sequence of immunoglobulin isotype involvement in infectious processes is important in modulating the cytokine response to bacteria and LPS by inflammatory cells. Our in vitro results support the critical role of sIgA in the proximal airways in mitigating inflammatory responses by other humoral defenses in the distal airways. Loss of effective sIgA function may contribute to increased morbidity and deaths from nosocomial pneumonia in compromised patients.

Mucosal lipocalin 2 has pro-inflammatory and iron-sequestering effects in response to bacterial enterobactin

Nasal colonization by both gram-positive and gram-negative pathogens induces expression of the innate immune protein lipocalin 2 (Lcn2). Lcn2 binds and sequesters the iron-scavenging siderophore enterobactin (Ent), preventing bacterial iron acquisition. In addition, Lcn2 bound to Ent induces release of IL-8 from cultured respiratory cells. As a countermeasure, pathogens of the Enterobacteriaceae family such as Klebsiella pneumoniae produce additional siderophores such as yersiniabactin (Ybt) and contain the iroA locus encoding an Ent glycosylase that prevents Lcn2 binding. Whereas the ability of Lcn2 to sequester iron is well described, the ability of Lcn2 to induce inflammation during infection is unknown. To study each potential effect of Lcn2 on colonization, we exploited K. pneumoniae mutants that are predicted to be susceptible to Lcn2-mediated iron sequestration (iroA ybtS mutant) or inflammation (iroA mutant), or to not interact with Lcn2 (entB mutant). During murine nasal colonization, the iroA ybtS double mutant was inhibited in an Lcn2-dependent manner, indicating that the iroA locus protects against Lcn2-mediated growth inhibition. Since the iroA single mutant was not inhibited, production of Ybt circumvents the iron sequestration effect of Lcn2 binding to Ent. However, colonization with the iroA mutant induced an increased influx of neutrophils compared to the entB mutant. This enhanced neutrophil response to Ent-producing K. pneumoniae was Lcn2-dependent. These findings suggest that Lcn2 has both pro-inflammatory and iron-sequestering effects along the respiratory mucosa in response to bacterial Ent. Therefore, Lcn2 may represent a novel mechanism of sensing microbial metabolism to modulate the host response appropriately.

Bacterial pathogens such as Klebsiella pneumoniae require iron and use secreted molecules called siderophores to strip iron from mammalian proteins. When bacteria colonize the upper respiratory tract, the mucosa secretes the protein lipocalin 2 (Lcn2) that binds to the siderophore enterobactin (Ent) and disrupts bacterial iron acquisition. In addition, Lcn2 bound to Ent stimulates release of the neutrophil-recruitment signal IL-8 from cultured respiratory cells. Some pathogens avoid Lcn2 binding by attaching glucose to Ent (to make Gly-Ent) or by making alternative siderophores. To determine the effect of Lcn2 on bacterial colonization, we colonized mice that express or lack Lcn2 with K. pneumoniae mutants that express or lack Ent, Gly-Ent and the alternative siderophore Yersiniabactin (Ybt). Our results indicate that mucosal Lcn2 inhibits colonization through iron sequestration and increases the influx of neutrophils in response to K. pneumoniae producing Ent. Therefore, Lcn2 acts as a barrier to colonization that pathogens must overcome to persist in the upper respiratory tract.

Beta2-microglobulin-dependent bacterial clearance and survival during murine Klebsiella pneumoniae bacteremia

Klebsiella pneumoniae is a leading cause of both community-acquired and nosocomial gram-negative bacterial pneumonia. A significant clinical complication of Klebsiella pulmonary infections is peripheral blood dissemination, resulting in a systemic infection concurrent with the localized pulmonary infection. We report here on the critical importance of beta(2)-microglobulin expression during murine K. pneumoniae bacteremia. Beta(2)-microglobulin knockout mice displayed significantly increased mortality upon intravenous inoculation that correlated with increased bacterial burden in the blood, liver, and spleen. As beta(2)-microglobulin knockout mice lack both CD8(+) T cells and invariant NK T cells, mouse models specifically deficient in either cell population were examined to see if this would account for the increased mortality noted in beta(2)-microglobulin knockout mice. Surprisingly, neither CD8 T-cell-deficient (TAP-1 knockout; in vivo anti-CD8 antibody treatment) nor invariant NK (iNK) T-cell-deficient (CD1d knockout, J alpha281 knockout) mice were more susceptible to K. pneumoniae bacteremia. Combined, these studies clearly indicate the importance of a beta(2)-microglobulin-dependent but CD8 T-cell- and iNK T-cell-independent mechanism critical for survival during K. pneumoniae bacteremia.

Increased weight loss with reduced viral replication in interleukin-10 knock-out mice infected with murine cytomegalovirus

The anti-inflammatory cytokine interleukin (IL)-10 plays an important role in the regulation of host-immune responses. Here we studied the role IL-10 plays in host responses to cytomegalovirus (CMV) infection. We demonstrate that manifestations of murine CMV (MCMV) disease are more severe in IL-10 knock-out mice, despite significantly reduced levels of viral replication. Cytokine analysis of serum revealed increased levels of interferon (IFN)-gamma, monocyte chemotactic protein 1 (MCP-1) and IL-6, all of which are potent stimulators of inflammatory responses. Depletion of IFN-gamma by monoclonal antibodies in IL-10 knock-out mice failed to improve the physical condition of the mice, while increasing viral replication. In contrast, serum levels of IL-6 in the knock-out animals were unaffected by IFN-gamma depletion and remained significantly elevated early in the course of infection. These data suggest that increased weight loss observed in IL-10 knock-out mice may be attributed to the uncontrolled production of proinflammatory cytokines, including IL-6.

Gene therapy for pulmonary diseases

Gene therapy has not yet met the high expectations of "the early days." However, it is a promising new treatment for lung diseases. Not only single gene disorders such as CF are potential candidates for gene therapy, but also cancer and chronic lung diseases characterized by an imbalance of damaging and protective mechanisms. This review summarizes the recent advances in the development of more efficient gene transfer systems and highlights areas of clinical application of gene therapy.

Inflammation--a new therapeutic target in pneumonia

Inflammation is a hallmark of pneumonia. Therefore, managing inflammation is an attractive adjunct to targeted antibiotic therapy, mainly in severe pneumonia. Recent investigations indicate that glucocorticoids given in physiological doses (from 10-fold to 100-fold less than doses administered in the past) could be of benefit. We could also manage inflammation by administering or influencing cytokines. A major concern is that drugs designed to target a single cytokine or receptor could prove ineffective due to the redundancy of signaling pathways involved. This may require selection of drugs with broad activity or the targeting of molecules common to inflammatory signaling pathways. Drugs affecting multiple molecules or key inflammatory pathway intermediates could be more effective, but their use will need to be weighed against the risk of impairing innate immunity. Indirect approaches to manage inflammation, such as neutralizing cytotoxic substances in the lung (e.g., inhibiting, neutralizing and eliminating endotoxin), could be used in combination with other approaches. Ideally, potential treatment of life-threatening bacterial pneumonia will combine immunoadjuvant and conventional antibiotic therapy, although intense clinical research with immunotherapy has not yet yielded a successful treatment adjunct. We believe that compounds capable of stimulating early host defense and microbial clearance, but not the later phases of inflammatory tissue injury associated with sepsis, may be advantageous.

Roles for early response cytokines during Escherichia coli pneumonia revealed by mice with combined deficiencies of all signaling receptors for TNF and IL-1

During infection, inflammation is essential for host defense, but it can injure tissues and compromise organ function. TNF-alpha and IL-1 (alpha and beta) are early response cytokines that facilitate inflammation. To determine the roles of these cytokines with overlapping functions, we generated mice deficient in all of the three receptors mediating their effects (TNFR1, TNFR2, and IL-1RI). During Escherichia coli pneumonia, receptor deficiency decreased neutrophil recruitment and edema accumulation to half of the levels observed in wild-type mice. Thus these receptors contributed to maximal responses, but substantial inflammation progressed independently of them. Receptor deficiency compromised antibacterial efficacy for some infectious doses. Decreased ventilation during E. coli pneumonia was not affected by receptor deficiency. However, the loss of lung compliance during pneumonia was substantially attenuated by receptor deficiency. Thus during E. coli pneumonia in mice, the lack of signaling from TNF-alpha and IL-1 decreases inflammation and preserves lung compliance.

Macrophage inflammatory protein 1alpha/CCL3 is required for clearance of an acute Klebsiella pneumoniae pulmonary infection

The objective of these studies was to determine the role of macrophage inflammatory protein 1alpha/CCL3 in pulmonary host defense during Klebsiella pneumoniae infection. Following intratracheal inoculation, 7-day survival of CCL3(-/-) mice was less than 10%, compared to 60% for CCL3(+/+) mice. Survival of CCR5(-/-) mice was equivalent to that of controls, indicating that the enhanced susceptibility of CCL3(-/-) mice to K. pneumoniae is mediated via another CCL3 receptor, presumably CCR1. At day 3, CFU burden in the lungs of CCL3(-/-) mice was 800-fold higher than in CCL3(+/+) mice, demonstrating that CCL3 is critical for control of bacterial growth in the lung. Surprisingly, CCL3(-/-) mice had no differences in the recruitment of monocytes/macrophages and even showed enhanced neutrophil recruitment at days 1, 2, and 3 postinfection, compared to CCL3(+/+) mice. Therefore, the defect in clearance was not due to insufficient recruitment of leukocytes. No significant differences in cytokine levels of monocyte chemoattractant protein 1 (MCP-1), interleukin 12, gamma interferon, or tumor necrosis factor alpha in lung lavages were found between CCL3(+/+) and CCL3(-/-) mice. CCL3(-/-) alveolar macrophages were found to have significantly lower phagocytic activity toward K. pneumoniae than CCL3(+/+) alveolar macrophages. These findings demonstrate that CCL3 production is critical for activation of alveolar macrophages to control the pulmonary growth of the gram-negative bacterium K. pneumoniae.